Adding --check to run a serials network test against GitHub or GHES. (#900)

* add --check.

docs/checks/actions.md

@@ -0,0 +1,44 @@
+
+# Actions Connection Check
+
+## What is this check for?
+
+Make sure the runner has access to actions service for GitHub.com or GitHub Enterprise Server
+
+- For GitHub.com
+  - The runner needs to access https://api.github.com for downloading actions.
+  - The runner needs to access https://vstoken.actions.githubusercontent.com/_apis/.../ for requesting an access token.
+  - The runner needs to access https://pipelines.actions.githubusercontent.com/_apis/.../ for receiving workflow jobs.
+- For GitHub Enterprise Server
+  - The runner needs to access https://myGHES.com/api/v3 for downloading actions.
+  - The runner needs to access https://myGHES.com/_services/vstoken/_apis/.../ for requesting an access token.
+  - The runner needs to access https://myGHES.com/_services/pipelines/_apis/.../ for receiving workflow jobs.
+
+## What is checked?
+
+- DNS lookup for api.github.com or myGHES.com using dotnet
+- Ping api.github.com or myGHES.com using dotnet
+- Make HTTP GET to https://api.github.com or https://myGHES.com/api/v3 using dotnet, check response headers contains `X-GitHub-Request-Id` 
+---
+- DNS lookup for vstoken.actions.githubusercontent.com using dotnet
+- Ping vstoken.actions.githubusercontent.com using dotnet
+- Make HTTP GET to https://vstoken.actions.githubusercontent.com/_apis/health or https://myGHES.com/_services/vstoken/_apis/health using dotnet, check response headers contains `x-vss-e2eid` 
+---
+- DNS lookup for pipelines.actions.githubusercontent.com using dotnet
+- Ping pipelines.actions.githubusercontent.com using dotnet
+- Make HTTP GET to https://pipelines.actions.githubusercontent.com/_apis/health or https://myGHES.com/_services/pipelines/_apis/health using dotnet, check response headers contains `x-vss-e2eid` 
+
+## How to fix the issue?
+
+### 1. Check the common network issue
+  
+  > Please check the [network doc](./network.md)
+
+### 2. SSL certificate related issue
+
+  If you are seeing `System.Net.Http.HttpRequestException: The SSL connection could not be established, see inner exception.` in the log, it means the runner can't connect to Actions service due to SSL handshake failure.
+  > Please check the [SSL cert doc](./sslcert.md)
+  
+## Still not working?
+
+Contact GitHub customer service or log an issue at https://github.com/actions/runner if you think it's a runner issue.

docs/checks/git.md

@@ -0,0 +1,34 @@
+# Git Connection Check
+
+## What is this check for?
+
+Make sure `git` can access GitHub.com or your GitHub Enterprise Server.
+
+
+## What is checked?
+
+The test is done by executing
+```bash
+# For GitHub.com
+git ls-remote --exit-code https://github.com/actions/checkout HEAD
+
+# For GitHub Enterprise Server
+git ls-remote --exit-code https://ghes.me/actions/checkout HEAD
+```
+
+The test also set environment variable `GIT_TRACE=1` and `GIT_CURL_VERBOSE=1` before running `git ls-remote`, this will make `git` to produce debug log for better debug any potential issues.
+
+## How to fix the issue?
+
+### 1. Check the common network issue
+  
+    > Please check the [network doc](./network.md)
+
+### 2. SSL certificate related issue
+
+  If you are seeing `SSL Certificate problem:` in the log, it means the `git` can't connect to the GitHub server due to SSL handshake failure.
+  > Please check the [SSL cert doc](./sslcert.md)
+  
+## Still not working?
+
+Contact GitHub customer service or log an issue at https://github.com/actions/runner if you think it's a runner issue.

docs/checks/internet.md

@@ -0,0 +1,26 @@
+# Internet Connection Check
+
+## What is this check for?
+
+Make sure the runner has access to https://api.github.com
+
+The runner needs to access https://api.github.com to download any actions from the marketplace.
+
+Even the runner is configured to GitHub Enterprise Server, the runner can still download actions from GitHub.com with [GitHub Connect](https://docs.github.com/en/enterprise-server@2.22/admin/github-actions/enabling-automatic-access-to-githubcom-actions-using-github-connect)
+
+
+## What is checked?
+
+- DNS lookup for api.github.com using dotnet
+- Ping api.github.com using dotnet
+- Make HTTP GET to https://api.github.com using dotnet, check response headers contains `X-GitHub-Request-Id` 
+
+## How to fix the issue?
+
+### 1. Check the common network issue
+  
+  > Please check the [network doc](./network.md)
+
+## Still not working?
+
+Contact GitHub customer service or log an issue at https://github.com/actions/runner if you think it's a runner issue.

docs/checks/network.md

@@ -0,0 +1,29 @@
+## Common Network Related Issues
+
+### Common things that can cause the runner to not working properly
+
+- Bug in the runner or the dotnet framework that causes actions runner can't make Http request in a certain network environment.
+
+- Proxy/Firewall block certain HTTP method, like it block all POST and PUT calls which the runner will use to upload logs.
+
+- Proxy/Firewall only allows requests with certain user-agent to pass through and the actions runner user-agent is not in the allow list.
+
+- Proxy try to decrypt and exam HTTPS traffic for security purpose but cause the actions-runner to fail to finish SSL handshake due to the lack of trusting proxy's CA.
+
+- Firewall rules that block action runner from accessing certain hosts, ex: `*.github.com`, `*.actions.githubusercontent.com`, etc.
+
+
+### Identify and solve these problems
+
+The key is to figure out where is the problem, the network environment, or the actions runner?
+
+Use a 3rd party tool to make the same requests as the runner did would be a good start point.
+
+- Use `nslookup` to check DNS
+- Use `ping` to check Ping
+- Use `curl -v` to check the network stack, good for verifying default certificate/proxy settings.
+- Use `Invoke-WebRequest` from `pwsh` (`PowerShell Core`) to check the dotnet network stack, good for verifying bugs in the dotnet framework.
+
+If the 3rd party tool is also experiencing the same error as the runner does, then you might want to contact your network administrator for help.
+
+Otherwise, contact GitHub customer support or log an issue at https://github.com/actions/runner

docs/checks/nodejs.md

@@ -0,0 +1,30 @@
+# Node.js Connection Check
+
+## What is this check for?
+
+Make sure the built-in node.js has access to GitHub.com or GitHub Enterprise Server.
+
+The runner carries it's own copy of node.js executable under `<runner_root>/externals/node12/`.
+
+All javascript base Actions will get executed by the built-in `node` at `<runner_root>/externals/node12/`.
+
+> Not the `node` from `$PATH`
+
+## What is checked?
+
+- Make HTTPS GET to https://api.github.com or https://myGHES.com/api/v3 using node.js, make sure it gets 200 response code.
+
+## How to fix the issue?
+
+### 1. Check the common network issue
+  
+  > Please check the [network doc](./network.md)
+
+### 2. SSL certificate related issue
+
+  If you are seeing `Https request failed due to SSL cert issue` in the log, it means the `node.js` can't connect to the GitHub server due to SSL handshake failure.
+  > Please check the [SSL cert doc](./sslcert.md)
+  
+## Still not working?
+
+Contact GitHub customer service or log an issue at https://github.com/actions/runner if you think it's a runner issue.

docs/checks/sslcert.md

@@ -0,0 +1,89 @@
+## SSL Certificate Related Issues
+
+You might run into an SSL certificate error when your GitHub Enterprise Server is using a self-signed SSL server certificate or a web proxy within your network is decrypting HTTPS traffic for a security audit.
+
+As long as your certificate is generated properly, most of the issues should be fixed after your trust the certificate properly on the runner machine.
+
+> Different OS might have extra requirements on SSL certificate,
+> Ex: macOS requires `ExtendedKeyUsage` https://support.apple.com/en-us/HT210176
+
+### Don't skip SSL cert validation
+
+> !!! DO NOT SKIP SSL CERT VALIDATION !!!  
+> !!! IT IS A BAD SECURITY PRACTICE !!!  
+
+### Download SSL certificate chain 
+
+Depends on how your SSL server certificate gets configured, you might need to download the whole certificate chain from a machine that has trusted the SSL certificate's CA.
+
+- Approach 1: Download certificate chain using a browser (Chrome, Firefox, IT), you can google for more example, [here is what I found](https://medium.com/@menakajain/export-download-ssl-certificate-from-server-site-url-bcfc41ea46a2)
+
+- Approach 2: Download certificate chain using OpenSSL, you can google for more example, [here is what I found](https://superuser.com/a/176721)
+
+- Approach 3: Ask your network administrator or the owner of the CA certificate to send you a copy of it
+
+### Trust CA certificate for the Runner
+
+The actions runner is a dotnet core application which will follow how dotnet load SSL CA certificates on each OS.
+
+You can get full details documentation at [here](https://docs.microsoft.com/en-us/dotnet/standard/security/cross-platform-cryptography#x509store)
+
+In short: 
+- Windows: Load from Windows certificate store.
+- Linux: Load from OpenSSL CA cert bundle.
+- macOS: Load from macOS KeyChain.
+
+To let the runner trusts your CA certificate, you will need to:
+1. Save your SSL certificate chain which includes the root CA and all intermediate CAs into a `.pem` file.
+2. Use `OpenSSL` to convert `.pem` file to a proper format for different OS, here is some [doc with sample commands](https://www.sslshopper.com/ssl-converter.html)
+3. Trust CA on different OS:
+    - Windows: https://docs.microsoft.com/en-us/skype-sdk/sdn/articles/installing-the-trusted-root-certificate
+    - macOS: ![trust ca cert](./../res/macOStrustCA.gif)
+    - Linux: Refer to the distribution documentation
+      1. RedHat: https://www.redhat.com/sysadmin/ca-certificates-cli
+      2. Ubuntu: http://manpages.ubuntu.com/manpages/focal/man8/update-ca-certificates.8.html
+      3. Google search: "trust ca certificate on [linux distribution]"
+      4. If all approaches failed, set environment variable `SSL_CERT_FILE` to the CA bundle `.pem` file we get. 
+    > To verity cert gets installed properly on Linux, you can try use `curl -v https://sitewithsslissue.com` and `pwsh -Command \"Invoke-WebRequest -Uri https://sitewithsslissue.com\"`
+
+### Trust CA certificate for Git CLI
+
+Git uses various CA bundle file depends on your operation system.
+- Git packaged the CA bundle file within the Git installation on Windows 
+- Git use OpenSSL certificate CA bundle file on Linux and macOS
+
+You can check where Git check CA file by running:
+```bash
+export GIT_CURL_VERBOSE=1
+git ls-remote https://github.com/actions/runner HEAD
+```
+
+You should see something like:
+```
+* Couldn't find host github.com in the .netrc file; using defaults
+*   Trying 140.82.114.4...
+* TCP_NODELAY set
+* Connected to github.com (140.82.114.4) port 443 (#0)
+* ALPN, offering h2
+* ALPN, offering http/1.1
+* successfully set certificate verify locations:
+*   CAfile: /etc/ssl/cert.pem
+  CApath: none
+* SSL connection using TLSv1.2 / ECDHE-RSA-AES128-GCM-SHA256
+```
+This tells me `/etc/ssl/cert.pem` is where it read trusted CA certificates.
+
+To let Git trusts your CA certificate, you will need to:
+1. Save your SSL certificate chain which includes the root CA and all intermediate CAs into a `.pem` file.
+2. Set `http.sslCAInfo` Git config or `GIT_SSL_CAINFO` environment variable to the full path of the `.pem` file [Git Doc](https://git-scm.com/docs/git-config#Documentation/git-config.txt-httpsslCAInfo)
+> I would recommend using `http.sslCAInfo` since it can be scope to certain hosts that need the extra trusted CA.  
+> Ex: `git config --global http.https://myghes.com/.sslCAInfo /extra/ca/cert.pem`  
+> This will make Git use the `/extra/ca/cert.pem` only when communicates with `https://myghes.com` and keep using the default CA bundle with others.
+
+### Trust CA certificate for Node.js
+
+Node.js has compiled a snapshot of the Mozilla CA store that is fixed at each version of Node.js' release time.
+
+To let Node.js trusts your CA certificate, you will need to:
+1. Save your SSL certificate chain which includes the root CA and all intermediate CAs into a `.pem` file.
+2. Set environment variable `NODE_EXTRA_CA_CERTS` which point to the file. ex: `export NODE_EXTRA_CA_CERTS=/full/path/to/cacert.pem` or `set NODE_EXTRA_CA_CERTS=C:\full\path\to\cacert.pem`

src/Misc/layoutbin/checkScripts/downloadCert.js

@@ -0,0 +1,115 @@
+const https = require('https')
+const fs = require('fs')
+const http = require('http')
+const hostname = process.env['HOSTNAME'] || ''
+const port = process.env['PORT'] || ''
+const path = process.env['PATH'] || ''
+const pat = process.env['PAT'] || ''
+const proxyHost = process.env['PROXYHOST'] || ''
+const proxyPort = process.env['PROXYPORT'] || ''
+const proxyUsername = process.env['PROXYUSERNAME'] || ''
+const proxyPassword = process.env['PROXYPASSWORD'] || ''
+
+process.env['NODE_TLS_REJECT_UNAUTHORIZED'] = '0'
+
+if (proxyHost === '') {
+    const options = {
+        hostname: hostname,
+        port: port,
+        path: path,
+        method: 'GET',
+        headers: {
+            'User-Agent': 'GitHubActionsRunnerCheck/1.0',
+            'Authorization': `token ${pat}`
+        },
+    }
+    const req = https.request(options, res => {
+        console.log(`statusCode: ${res.statusCode}`)
+        console.log(`headers: ${JSON.stringify(res.headers)}`)
+        let cert = socket.getPeerCertificate(true)
+        let certPEM = ''
+        let fingerprints = {}
+        while (cert != null && fingerprints[cert.fingerprint] != '1') {
+            fingerprints[cert.fingerprint] = '1'
+            certPEM = certPEM + '-----BEGIN CERTIFICATE-----\n'
+            let certEncoded = cert.raw.toString('base64')
+            for (let i = 0; i < certEncoded.length; i++) {
+                certPEM = certPEM + certEncoded[i]
+                if (i != certEncoded.length - 1 && (i + 1) % 64 == 0) {
+                    certPEM = certPEM + '\n'
+                }
+            }
+            certPEM = certPEM + '\n-----END CERTIFICATE-----\n'
+            cert = cert.issuerCertificate
+        }
+        console.log(certPEM)
+        fs.writeFileSync('./download_ca_cert.pem', certPEM)
+        res.on('data', d => {
+            process.stdout.write(d)
+        })
+    })
+    req.on('error', error => {
+        console.error(error)
+    })
+    req.end()
+}
+else {
+    const auth = 'Basic ' + Buffer.from(proxyUsername + ':' + proxyPassword).toString('base64')
+
+    const options = {
+        host: proxyHost,
+        port: proxyPort,
+        method: 'CONNECT',
+        path: `${hostname}:${port}`,
+    }
+
+    if (proxyUsername != '' || proxyPassword != '') {
+        options.headers = {
+            'Proxy-Authorization': auth,
+        }
+    }
+
+    http.request(options).on('connect', (res, socket) => {
+        if (res.statusCode != 200) {
+            throw new Error(`Proxy returns code: ${res.statusCode}`)
+        }
+
+        https.get({
+            host: hostname,
+            port: port,
+            socket: socket,
+            agent: false,
+            path: '/',
+            headers: {
+                'User-Agent': 'GitHubActionsRunnerCheck/1.0',
+                'Authorization': `token ${pat}`
+            }
+        }, (res) => {
+            let cert = res.socket.getPeerCertificate(true)
+            let certPEM = ''
+            let fingerprints = {}
+            while (cert != null && fingerprints[cert.fingerprint] != '1') {
+                fingerprints[cert.fingerprint] = '1'
+                certPEM = certPEM + '-----BEGIN CERTIFICATE-----\n'
+                let certEncoded = cert.raw.toString('base64')
+                for (let i = 0; i < certEncoded.length; i++) {
+                    certPEM = certPEM + certEncoded[i]
+                    if (i != certEncoded.length - 1 && (i + 1) % 64 == 0) {
+                        certPEM = certPEM + '\n'
+                    }
+                }
+                certPEM = certPEM + '\n-----END CERTIFICATE-----\n'
+                cert = cert.issuerCertificate
+            }
+            console.log(certPEM)
+            fs.writeFileSync('./download_ca_cert.pem', certPEM)
+            console.log(`statusCode: ${res.statusCode}`)
+            console.log(`headers: ${JSON.stringify(res.headers)}`)
+            res.on('data', d => {
+                process.stdout.write(d)
+            })
+        })
+    }).on('error', (err) => {
+        console.error('error', err)
+    }).end()
+}

src/Misc/layoutbin/checkScripts/makeWebRequest.js

@@ -0,0 +1,75 @@
+const https = require('https')
+const http = require('http')
+const hostname = process.env['HOSTNAME'] || ''
+const port = process.env['PORT'] || ''
+const path = process.env['PATH'] || ''
+const pat = process.env['PAT'] || ''
+const proxyHost = process.env['PROXYHOST'] || ''
+const proxyPort = process.env['PROXYPORT'] || ''
+const proxyUsername = process.env['PROXYUSERNAME'] || ''
+const proxyPassword = process.env['PROXYPASSWORD'] || ''
+
+if (proxyHost === '') {
+    const options = {
+        hostname: hostname,
+        port: port,
+        path: path,
+        method: 'GET',
+        headers: {
+            'User-Agent': 'GitHubActionsRunnerCheck/1.0',
+            'Authorization': `token ${pat}`,
+        }
+    }
+    const req = https.request(options, res => {
+        console.log(`statusCode: ${res.statusCode}`)
+        console.log(`headers: ${JSON.stringify(res.headers)}`)
+
+        res.on('data', d => {
+            process.stdout.write(d)
+        })
+    })
+    req.on('error', error => {
+        console.error(error)
+    })
+    req.end()
+}
+else {
+    const proxyAuth = 'Basic ' + Buffer.from(proxyUsername + ':' + proxyPassword).toString('base64')
+    const options = {
+        hostname: proxyHost,
+        port: proxyPort,
+        method: 'CONNECT',
+        path: `${hostname}:${port}`
+    }
+
+    if (proxyUsername != '' || proxyPassword != '') {
+        options.headers = {
+            'Proxy-Authorization': proxyAuth,
+        }
+    }
+    http.request(options).on('connect', (res, socket) => {
+        if (res.statusCode != 200) {
+            throw new Error(`Proxy returns code: ${res.statusCode}`)
+        }
+        https.get({
+            host: hostname,
+            port: port,
+            socket: socket,
+            agent: false,
+            path: path,
+            headers: {
+                'User-Agent': 'GitHubActionsRunnerCheck/1.0',
+                'Authorization': `token ${pat}`,
+            }
+        }, (res) => {
+            console.log(`statusCode: ${res.statusCode}`)
+            console.log(`headers: ${JSON.stringify(res.headers)}`)
+
+            res.on('data', d => {
+                process.stdout.write(d)
+            })
+        })
+    }).on('error', (err) => {
+        console.error('error', err)
+    }).end()
+}

src/Runner.Common/Constants.cs

@@ -121,6 +121,7 @@ namespace GitHub.Runner.Common
                 //validFlags array as well present in the CommandSettings.cs
                 public static class Flags
                 {
+                    public static readonly string Check = "check";
                     public static readonly string Commit = "commit";
                     public static readonly string Help = "help";
                     public static readonly string Replace = "replace";

src/Runner.Common/ExtensionManager.cs

@@ -60,6 +60,12 @@ namespace GitHub.Runner.Common
                     Add<T>(extensions, "GitHub.Runner.Worker.AddPathFileCommand, Runner.Worker");
                     Add<T>(extensions, "GitHub.Runner.Worker.SetEnvFileCommand, Runner.Worker");
                     break;
+                case "GitHub.Runner.Listener.Check.ICheckExtension":
+                    Add<T>(extensions, "GitHub.Runner.Listener.Check.InternetCheck, Runner.Listener");
+                    Add<T>(extensions, "GitHub.Runner.Listener.Check.ActionsCheck, Runner.Listener");
+                    Add<T>(extensions, "GitHub.Runner.Listener.Check.GitCheck, Runner.Listener");
+                    Add<T>(extensions, "GitHub.Runner.Listener.Check.NodeJsCheck, Runner.Listener");
+                    break;
                 default:
                     // This should never happen.
                     throw new NotSupportedException($"Unexpected extension type: '{typeof(T).FullName}'");

src/Runner.Listener/Checks/ActionsCheck.cs

@@ -0,0 +1,90 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using GitHub.Runner.Common;
+using GitHub.Runner.Sdk;
+
+namespace GitHub.Runner.Listener.Check
+{
+    public sealed class ActionsCheck : RunnerService, ICheckExtension
+    {
+        private string _logFile = null;
+
+        public int Order => 2;
+
+        public string CheckName => "GitHub Actions Connection";
+
+        public string CheckDescription => "Make sure the actions runner have access to the GitHub Actions Service.";
+
+        public string CheckLog => _logFile;
+
+        public string HelpLink => "https://github.com/actions/runner/blob/main/docs/checks/actions.md";
+
+        public Type ExtensionType => typeof(ICheckExtension);
+
+        public override void Initialize(IHostContext hostContext)
+        {
+            base.Initialize(hostContext);
+            _logFile = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Diag), StringUtil.Format("{0}_{1:yyyyMMdd-HHmmss}-utc.log", nameof(ActionsCheck), DateTime.UtcNow));
+        }
+
+        // runner access to actions service
+        public async Task<bool> RunCheck(string url, string pat)
+        {
+            await File.AppendAllLinesAsync(_logFile, HostContext.WarnLog());
+            await File.AppendAllLinesAsync(_logFile, HostContext.CheckProxy());
+
+            var checkTasks = new List<Task<CheckResult>>();
+            string githubApiUrl = null;
+            string actionsTokenServiceUrl = null;
+            string actionsPipelinesServiceUrl = null;
+            var urlBuilder = new UriBuilder(url);
+            if (UrlUtil.IsHostedServer(urlBuilder))
+            {
+                urlBuilder.Host = $"api.{urlBuilder.Host}";
+                urlBuilder.Path = "";
+                githubApiUrl = urlBuilder.Uri.AbsoluteUri;
+                actionsTokenServiceUrl = "https://vstoken.actions.githubusercontent.com/_apis/health";
+                actionsPipelinesServiceUrl = "https://pipelines.actions.githubusercontent.com/_apis/health";
+            }
+            else
+            {
+                urlBuilder.Path = "api/v3";
+                githubApiUrl = urlBuilder.Uri.AbsoluteUri;
+                urlBuilder.Path = "_services/vstoken/_apis/health";
+                actionsTokenServiceUrl = urlBuilder.Uri.AbsoluteUri;
+                urlBuilder.Path = "_services/pipelines/_apis/health";
+                actionsPipelinesServiceUrl = urlBuilder.Uri.AbsoluteUri;
+            }
+
+            // check github api
+            checkTasks.Add(CheckUtil.CheckDns(githubApiUrl));
+            checkTasks.Add(CheckUtil.CheckPing(githubApiUrl));
+            checkTasks.Add(HostContext.CheckHttpsRequests(githubApiUrl, pat, expectedHeader: "X-GitHub-Request-Id"));
+
+            // check actions token service
+            checkTasks.Add(CheckUtil.CheckDns(actionsTokenServiceUrl));
+            checkTasks.Add(CheckUtil.CheckPing(actionsTokenServiceUrl));
+            checkTasks.Add(HostContext.CheckHttpsRequests(actionsTokenServiceUrl, pat, expectedHeader: "x-vss-e2eid"));
+
+            // check actions pipelines service
+            checkTasks.Add(CheckUtil.CheckDns(actionsPipelinesServiceUrl));
+            checkTasks.Add(CheckUtil.CheckPing(actionsPipelinesServiceUrl));
+            checkTasks.Add(HostContext.CheckHttpsRequests(actionsPipelinesServiceUrl, pat, expectedHeader: "x-vss-e2eid"));
+
+            var result = true;
+            while (checkTasks.Count > 0)
+            {
+                var finishedCheckTask = await Task.WhenAny<CheckResult>(checkTasks);
+                var finishedCheck = await finishedCheckTask;
+                result = result && finishedCheck.Pass;
+                await File.AppendAllLinesAsync(_logFile, finishedCheck.Logs);
+                checkTasks.Remove(finishedCheckTask);
+            }
+
+            await Task.WhenAll(checkTasks);
+            return result;
+        }
+    }
+}

src/Runner.Listener/Checks/CheckUtil.cs

@@ -0,0 +1,351 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.Tracing;
+using System.IO;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using System.Net.NetworkInformation;
+using System.Threading;
+using System.Threading.Tasks;
+using GitHub.Runner.Common;
+using GitHub.Runner.Sdk;
+using GitHub.Services.Common;
+
+namespace GitHub.Runner.Listener.Check
+{
+    public static class CheckUtil
+    {
+        public static List<string> WarnLog(this IHostContext hostContext)
+        {
+            var logs = new List<string>();
+            logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+            logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+            logs.Add($"{DateTime.UtcNow.ToString("O")} ****     !!! WARNING !!! ");
+            logs.Add($"{DateTime.UtcNow.ToString("O")} ****     DO NOT share the log in public place! The log may contains secrets in plain text. ");
+            logs.Add($"{DateTime.UtcNow.ToString("O")} ****     !!! WARNING !!! ");
+            logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+            logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+            return logs;
+        }
+
+        public static List<string> CheckProxy(this IHostContext hostContext)
+        {
+            var logs = new List<string>();
+            if (!string.IsNullOrEmpty(hostContext.WebProxy.HttpProxyAddress) ||
+                !string.IsNullOrEmpty(hostContext.WebProxy.HttpsProxyAddress))
+            {
+                logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Runner is behind web proxy {hostContext.WebProxy.HttpsProxyAddress ?? hostContext.WebProxy.HttpProxyAddress} ");
+                logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+            }
+
+            return logs;
+        }
+
+        public static async Task<CheckResult> CheckDns(string targetUrl)
+        {
+            var result = new CheckResult();
+            var url = new Uri(targetUrl);
+            try
+            {
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Try DNS lookup for {url.Host} ");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                IPHostEntry host = await Dns.GetHostEntryAsync(url.Host);
+                foreach (var address in host.AddressList)
+                {
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Resolved DNS for {url.Host} to '{address}'");
+                }
+
+                result.Pass = true;
+            }
+            catch (Exception ex)
+            {
+                result.Pass = false;
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Resolved DNS for {url.Host} failed with error: {ex}");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+            }
+
+            return result;
+        }
+
+        public static async Task<CheckResult> CheckPing(string targetUrl)
+        {
+            var result = new CheckResult();
+            var url = new Uri(targetUrl);
+            try
+            {
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Try ping {url.Host} ");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                using (var ping = new Ping())
+                {
+                    var reply = await ping.SendPingAsync(url.Host);
+                    if (reply.Status == IPStatus.Success)
+                    {
+                        result.Pass = true;
+                        result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Ping {url.Host} ({reply.Address}) succeed within to '{reply.RoundtripTime} ms'");
+                    }
+                    else
+                    {
+                        result.Pass = false;
+                        result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Ping {url.Host} ({reply.Address}) failed with '{reply.Status}'");
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                result.Pass = false;
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Ping api.github.com failed with error: {ex}");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+            }
+
+            return result;
+        }
+
+        public static async Task<CheckResult> CheckHttpsRequests(this IHostContext hostContext, string url, string pat, string expectedHeader)
+        {
+            var result = new CheckResult();
+            try
+            {
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Send HTTPS Request to {url} ");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                using (var _ = new HttpEventSourceListener(result.Logs))
+                using (var httpClientHandler = hostContext.CreateHttpClientHandler())
+                using (var httpClient = new HttpClient(httpClientHandler))
+                {
+                    httpClient.DefaultRequestHeaders.UserAgent.AddRange(hostContext.UserAgents);
+                    if (!string.IsNullOrEmpty(pat))
+                    {
+                        httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("token", pat);
+                    }
+
+                    var response = await httpClient.GetAsync(url);
+
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Http status code: {response.StatusCode}");
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Http response headers: {response.Headers}");
+
+                    var responseContent = await response.Content.ReadAsStringAsync();
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Http response body: {responseContent}");
+                    if (response.IsSuccessStatusCode)
+                    {
+                        if (response.Headers.Contains(expectedHeader))
+                        {
+                            result.Pass = true;
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Http request 'GET' to {url} succeed");
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ");
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ");
+                        }
+                        else
+                        {
+                            result.Pass = false;
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Http request 'GET' to {url} succeed but doesn't have expected HTTP Header.");
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ");
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ");
+                        }
+                    }
+                    else
+                    {
+                        result.Pass = false;
+                        result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                        result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Http request 'GET' to {url} failed with {response.StatusCode}");
+                        result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                        result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ");
+                        result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ");
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                result.Pass = false;
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Https request 'GET' to {url} failed with error: {ex}");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+            }
+
+            return result;
+        }
+
+        public static async Task<CheckResult> DownloadExtraCA(this IHostContext hostContext, string url, string pat)
+        {
+            var result = new CheckResult();
+            try
+            {
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Download SSL Certificate from {url} ");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+
+                var uri = new Uri(url);
+                var env = new Dictionary<string, string>()
+                {
+                    { "HOSTNAME", uri.Host },
+                    { "PORT", uri.IsDefaultPort ? (uri.Scheme.ToLowerInvariant() == "https" ? "443" : "80") : uri.Port.ToString() },
+                    { "PATH", uri.AbsolutePath },
+                    { "PAT", pat }
+                };
+
+                var proxy = hostContext.WebProxy.GetProxy(uri);
+                if (proxy != null)
+                {
+                    env["PROXYHOST"] = proxy.Host;
+                    env["PROXYPORT"] = proxy.IsDefaultPort ? (proxy.Scheme.ToLowerInvariant() == "https" ? "443" : "80") : proxy.Port.ToString();
+                    if (hostContext.WebProxy.HttpProxyUsername != null ||
+                        hostContext.WebProxy.HttpsProxyUsername != null)
+                    {
+                        env["PROXYUSERNAME"] = hostContext.WebProxy.HttpProxyUsername ?? hostContext.WebProxy.HttpsProxyUsername;
+                        env["PROXYPASSWORD"] = hostContext.WebProxy.HttpProxyPassword ?? hostContext.WebProxy.HttpsProxyPassword;
+                    }
+                    else
+                    {
+                        env["PROXYUSERNAME"] = "";
+                        env["PROXYPASSWORD"] = "";
+                    }
+                }
+                else
+                {
+                    env["PROXYHOST"] = "";
+                    env["PROXYPORT"] = "";
+                    env["PROXYUSERNAME"] = "";
+                    env["PROXYPASSWORD"] = "";
+                }
+
+                using (var processInvoker = hostContext.CreateService<IProcessInvoker>())
+                {
+                    processInvoker.OutputDataReceived += new EventHandler<ProcessDataReceivedEventArgs>((sender, args) =>
+                    {
+                        if (!string.IsNullOrEmpty(args.Data))
+                        {
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} [STDOUT] {args.Data}");
+                        }
+                    });
+
+                    processInvoker.ErrorDataReceived += new EventHandler<ProcessDataReceivedEventArgs>((sender, args) =>
+                    {
+                        if (!string.IsNullOrEmpty(args.Data))
+                        {
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} [STDERR] {args.Data}");
+                        }
+                    });
+
+                    var downloadCertScript = Path.Combine(hostContext.GetDirectory(WellKnownDirectory.Bin), "checkScripts", "downloadCert");
+                    var node12 = Path.Combine(hostContext.GetDirectory(WellKnownDirectory.Externals), "node12", "bin", $"node{IOUtil.ExeExtension}");
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Run '{node12} \"{downloadCertScript}\"' ");
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} {StringUtil.ConvertToJson(env)}");
+                    await processInvoker.ExecuteAsync(
+                        hostContext.GetDirectory(WellKnownDirectory.Root),
+                        node12,
+                        $"\"{downloadCertScript}\"",
+                        env,
+                        true,
+                        CancellationToken.None);
+                }
+
+                result.Pass = true;
+            }
+            catch (Exception ex)
+            {
+                result.Pass = false;
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Download SSL Certificate from '{url}' failed with error: {ex}");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+            }
+
+            return result;
+        }
+    }
+
+    // EventSource listener for dotnet debug trace for HTTP and SSL
+    public sealed class HttpEventSourceListener : EventListener
+    {
+        private readonly List<string> _logs;
+        private readonly object _lock = new object();
+        private readonly Dictionary<string, HashSet<string>> _ignoredEvent = new Dictionary<string, HashSet<string>>
+        {
+            {
+                "Private.InternalDiagnostics.System.Net.Http",
+                new HashSet<string>
+                {
+                    "Info",
+                    "Associate"
+                }
+            },
+            {
+                "Private.InternalDiagnostics.System.Net.Security",
+                new HashSet<string>
+                {
+                    "Info",
+                    "SslStreamCtor",
+                    "SecureChannelCtor",
+                    "NoDelegateNoClientCert",
+                    "CertsAfterFiltering",
+                    "UsingCachedCredential",
+                    "SspiSelectedCipherSuite"
+                }
+            }
+        };
+
+        public HttpEventSourceListener(List<string> logs)
+        {
+            _logs = logs;
+            if (Environment.GetEnvironmentVariable("ACTIONS_RUNNER_TRACE_ALL_HTTP_EVENT") == "1")
+            {
+                _ignoredEvent.Clear();
+            }
+        }
+
+        protected override void OnEventSourceCreated(EventSource eventSource)
+        {
+            base.OnEventSourceCreated(eventSource);
+
+            if (eventSource.Name == "Private.InternalDiagnostics.System.Net.Http" ||
+                eventSource.Name == "Private.InternalDiagnostics.System.Net.Security")
+            {
+                EnableEvents(eventSource, EventLevel.Verbose, EventKeywords.All);
+            }
+        }
+
+        protected override void OnEventWritten(EventWrittenEventArgs eventData)
+        {
+            base.OnEventWritten(eventData);
+            lock (_lock)
+            {
+                if (_ignoredEvent.TryGetValue(eventData.EventSource.Name, out var ignored) &&
+                    ignored.Contains(eventData.EventName))
+                {
+                    return;
+                }
+
+                _logs.Add($"{DateTime.UtcNow.ToString("O")} [START {eventData.EventSource.Name} - {eventData.EventName}]");
+                _logs.AddRange(eventData.Payload.Select(x => string.Join(Environment.NewLine, x.ToString().Split(Environment.NewLine).Select(y => $"{DateTime.UtcNow.ToString("O")} {y}"))));
+                _logs.Add($"{DateTime.UtcNow.ToString("O")} [END {eventData.EventSource.Name} - {eventData.EventName}]");
+            }
+        }
+    }
+}

src/Runner.Listener/Checks/GitCheck.cs

@@ -0,0 +1,171 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net;
+using System.Threading;
+using System.Threading.Tasks;
+using GitHub.Runner.Common;
+using GitHub.Runner.Sdk;
+
+namespace GitHub.Runner.Listener.Check
+{
+    public sealed class GitCheck : RunnerService, ICheckExtension
+    {
+        private string _logFile = null;
+        private string _gitPath = null;
+
+        public int Order => 3;
+
+        public string CheckName => "Git Certificate/Proxy Validation";
+
+        public string CheckDescription => "Make sure the git cli can access to GitHub.com or the GitHub Enterprise Server.";
+
+        public string CheckLog => _logFile;
+
+        public string HelpLink => "https://github.com/actions/runner/blob/main/docs/checks/git.md";
+
+        public Type ExtensionType => typeof(ICheckExtension);
+
+        public override void Initialize(IHostContext hostContext)
+        {
+            base.Initialize(hostContext);
+            _logFile = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Diag), StringUtil.Format("{0}_{1:yyyyMMdd-HHmmss}-utc.log", nameof(GitCheck), DateTime.UtcNow));
+            _gitPath = WhichUtil.Which("git");
+        }
+
+        // git access to ghes/gh 
+        public async Task<bool> RunCheck(string url, string pat)
+        {
+            await File.AppendAllLinesAsync(_logFile, HostContext.WarnLog());
+            await File.AppendAllLinesAsync(_logFile, HostContext.CheckProxy());
+
+            if (string.IsNullOrEmpty(_gitPath))
+            {
+                await File.AppendAllLinesAsync(_logFile, new[] { $"{DateTime.UtcNow.ToString("O")} Can't verify git with GitHub.com or GitHub Enterprise Server since git is not installed." });
+                return false;
+            }
+
+            var checkGit = await CheckGit(url, pat);
+            var result = checkGit.Pass;
+            await File.AppendAllLinesAsync(_logFile, checkGit.Logs);
+
+            // try fix SSL error by providing extra CA certificate.
+            if (checkGit.SslError)
+            {
+                await File.AppendAllLinesAsync(_logFile, new[] { $"{DateTime.UtcNow.ToString("O")} Try fix SSL error by providing extra CA certificate." });
+                var downloadCert = await HostContext.DownloadExtraCA(url, pat);
+                await File.AppendAllLinesAsync(_logFile, downloadCert.Logs);
+
+                if (downloadCert.Pass)
+                {
+                    var recheckGit = await CheckGit(url, pat, extraCA: true);
+                    await File.AppendAllLinesAsync(_logFile, recheckGit.Logs);
+                    if (recheckGit.Pass)
+                    {
+                        await File.AppendAllLinesAsync(_logFile, new[] { $"{DateTime.UtcNow.ToString("O")} Fixed SSL error by providing extra CA certs." });
+                    }
+                }
+            }
+
+            return result;
+        }
+
+        private async Task<CheckResult> CheckGit(string url, string pat, bool extraCA = false)
+        {
+            var result = new CheckResult();
+            try
+            {
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Validate server cert and proxy configuration with Git ");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                var repoUrlBuilder = new UriBuilder(url);
+                repoUrlBuilder.Path = "actions/checkout";
+                repoUrlBuilder.UserName = "gh";
+                repoUrlBuilder.Password = pat;
+
+                var gitProxy = "";
+                var proxy = HostContext.WebProxy.GetProxy(repoUrlBuilder.Uri);
+                if (proxy != null)
+                {
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Runner is behind http proxy '{proxy.AbsoluteUri}'");
+                    if (HostContext.WebProxy.HttpProxyUsername != null ||
+                        HostContext.WebProxy.HttpsProxyUsername != null)
+                    {
+                        var proxyUrlWithCred = UrlUtil.GetCredentialEmbeddedUrl(
+                            proxy,
+                            HostContext.WebProxy.HttpProxyUsername ?? HostContext.WebProxy.HttpsProxyUsername,
+                            HostContext.WebProxy.HttpProxyPassword ?? HostContext.WebProxy.HttpsProxyPassword);
+                        gitProxy = $"-c http.proxy={proxyUrlWithCred}";
+                    }
+                    else
+                    {
+                        gitProxy = $"-c http.proxy={proxy.AbsoluteUri}";
+                    }
+                }
+
+                using (var processInvoker = HostContext.CreateService<IProcessInvoker>())
+                {
+                    processInvoker.OutputDataReceived += new EventHandler<ProcessDataReceivedEventArgs>((sender, args) =>
+                    {
+                        if (!string.IsNullOrEmpty(args.Data))
+                        {
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} {args.Data}");
+                        }
+                    });
+
+                    processInvoker.ErrorDataReceived += new EventHandler<ProcessDataReceivedEventArgs>((sender, args) =>
+                    {
+                        if (!string.IsNullOrEmpty(args.Data))
+                        {
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} {args.Data}");
+                        }
+                    });
+
+                    var gitArgs = $"{gitProxy} ls-remote --exit-code {repoUrlBuilder.Uri.AbsoluteUri} HEAD";
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Run 'git {gitArgs}' ");
+
+                    var env = new Dictionary<string, string>
+                    {
+                        { "GIT_TRACE", "1" },
+                        { "GIT_CURL_VERBOSE", "1" }
+                    };
+
+                    if (extraCA)
+                    {
+                        env["GIT_SSL_CAINFO"] = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Root), "download_ca_cert.pem");
+                    }
+
+                    await processInvoker.ExecuteAsync(
+                        HostContext.GetDirectory(WellKnownDirectory.Root),
+                        _gitPath,
+                        gitArgs,
+                        env,
+                        true,
+                        CancellationToken.None);
+                }
+
+                result.Pass = true;
+            }
+            catch (Exception ex)
+            {
+                result.Pass = false;
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     git ls-remote failed with error: {ex}");
+                if (result.Logs.Any(x => x.Contains("SSL Certificate problem", StringComparison.OrdinalIgnoreCase)))
+                {
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     git ls-remote failed due to SSL cert issue.");
+                    result.SslError = true;
+                }
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+
+            }
+
+            return result;
+        }
+    }
+}

src/Runner.Listener/Checks/ICheckExtension.cs

@@ -0,0 +1,30 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using GitHub.Runner.Common;
+
+namespace GitHub.Runner.Listener.Check
+{
+    public interface ICheckExtension : IExtension
+    {
+        int Order { get; }
+        string CheckName { get; }
+        string CheckDescription { get; }
+        string CheckLog { get; }
+        string HelpLink { get; }
+        Task<bool> RunCheck(string url, string pat);
+    }
+
+    public class CheckResult
+    {
+        public CheckResult()
+        {
+            Logs = new List<string>();
+        }
+
+        public bool Pass { get; set; }
+
+        public bool SslError { get; set; }
+
+        public List<string> Logs { get; set; }
+    }
+}

src/Runner.Listener/Checks/InternetCheck.cs

@@ -0,0 +1,59 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using GitHub.Runner.Common;
+using GitHub.Runner.Sdk;
+
+namespace GitHub.Runner.Listener.Check
+{
+    public sealed class InternetCheck : RunnerService, ICheckExtension
+    {
+        private string _logFile = null;
+
+        public int Order => 1;
+
+        public string CheckName => "Internet Connection";
+
+        public string CheckDescription => "Make sure the actions runner have access to public internet.";
+
+        public string CheckLog => _logFile;
+
+        public string HelpLink => "https://github.com/actions/runner/blob/main/docs/checks/internet.md";
+
+        public Type ExtensionType => typeof(ICheckExtension);
+
+        public override void Initialize(IHostContext hostContext)
+        {
+            base.Initialize(hostContext);
+            _logFile = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Diag), StringUtil.Format("{0}_{1:yyyyMMdd-HHmmss}-utc.log", nameof(InternetCheck), DateTime.UtcNow));
+        }
+
+        // check runner access to api.github.com
+        public async Task<bool> RunCheck(string url, string pat)
+        {
+            await File.AppendAllLinesAsync(_logFile, HostContext.WarnLog());
+            await File.AppendAllLinesAsync(_logFile, HostContext.CheckProxy());
+
+            var checkTasks = new List<Task<CheckResult>>();
+            checkTasks.Add(CheckUtil.CheckDns("https://api.github.com"));
+            checkTasks.Add(CheckUtil.CheckPing("https://api.github.com"));
+
+            // We don't need to pass a PAT since it might be a token for GHES.
+            checkTasks.Add(HostContext.CheckHttpsRequests("https://api.github.com", pat: null, expectedHeader: "X-GitHub-Request-Id"));
+
+            var result = true;
+            while (checkTasks.Count > 0)
+            {
+                var finishedCheckTask = await Task.WhenAny<CheckResult>(checkTasks);
+                var finishedCheck = await finishedCheckTask;
+                result = result && finishedCheck.Pass;
+                await File.AppendAllLinesAsync(_logFile, finishedCheck.Logs);
+                checkTasks.Remove(finishedCheckTask);
+            }
+
+            await Task.WhenAll(checkTasks);
+            return result;
+        }
+    }
+}

src/Runner.Listener/Checks/NodeJsCheck.cs

@@ -0,0 +1,181 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net;
+using System.Threading;
+using System.Threading.Tasks;
+using GitHub.Runner.Common;
+using GitHub.Runner.Sdk;
+
+namespace GitHub.Runner.Listener.Check
+{
+    public sealed class NodeJsCheck : RunnerService, ICheckExtension
+    {
+        private string _logFile = null;
+
+        public int Order => 4;
+
+        public string CheckName => "Node.js Certificate/Proxy Validation";
+
+        public string CheckDescription => "Make sure the node.js have access to GitHub.com or the GitHub Enterprise Server.";
+
+        public string CheckLog => _logFile;
+
+        public string HelpLink => "https://github.com/actions/runner/blob/main/docs/checks/nodejs.md";
+
+        public Type ExtensionType => typeof(ICheckExtension);
+
+        public override void Initialize(IHostContext hostContext)
+        {
+            base.Initialize(hostContext);
+            _logFile = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Diag), StringUtil.Format("{0}_{1:yyyyMMdd-HHmmss}-utc.log", nameof(NodeJsCheck), DateTime.UtcNow));
+        }
+
+        // node access to ghes/gh
+        public async Task<bool> RunCheck(string url, string pat)
+        {
+            await File.AppendAllLinesAsync(_logFile, HostContext.WarnLog());
+            await File.AppendAllLinesAsync(_logFile, HostContext.CheckProxy());
+
+            // Request to github.com or ghes server
+            var urlBuilder = new UriBuilder(url);
+            if (UrlUtil.IsHostedServer(urlBuilder))
+            {
+                urlBuilder.Host = $"api.{urlBuilder.Host}";
+                urlBuilder.Path = "";
+            }
+            else
+            {
+                urlBuilder.Path = "api/v3";
+            }
+
+            var checkNode = await CheckNodeJs(urlBuilder.Uri.AbsoluteUri, pat);
+            var result = checkNode.Pass;
+            await File.AppendAllLinesAsync(_logFile, checkNode.Logs);
+
+            // try fix SSL error by providing extra CA certificate.
+            if (checkNode.SslError)
+            {
+                var downloadCert = await HostContext.DownloadExtraCA(urlBuilder.Uri.AbsoluteUri, pat);
+                await File.AppendAllLinesAsync(_logFile, downloadCert.Logs);
+
+                if (downloadCert.Pass)
+                {
+                    var recheckNode = await CheckNodeJs(urlBuilder.Uri.AbsoluteUri, pat, extraCA: true);
+                    await File.AppendAllLinesAsync(_logFile, recheckNode.Logs);
+                    if (recheckNode.Pass)
+                    {
+                        await File.AppendAllLinesAsync(_logFile, new[] { $"{DateTime.UtcNow.ToString("O")} Fixed SSL error by providing extra CA certs." });
+                    }
+                }
+            }
+
+            return result;
+        }
+
+        private async Task<CheckResult> CheckNodeJs(string url, string pat, bool extraCA = false)
+        {
+            var result = new CheckResult();
+            try
+            {
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Make Http request to {url} using node.js ");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+
+                // Request to github.com or ghes server
+                Uri requestUrl = new Uri(url);
+                var env = new Dictionary<string, string>()
+                {
+                    { "HOSTNAME", requestUrl.Host },
+                    { "PORT", requestUrl.IsDefaultPort ? (requestUrl.Scheme.ToLowerInvariant() == "https" ? "443" : "80") : requestUrl.Port.ToString() },
+                    { "PATH", requestUrl.AbsolutePath },
+                    { "PAT", pat }
+                };
+
+                var proxy = HostContext.WebProxy.GetProxy(requestUrl);
+                if (proxy != null)
+                {
+                    env["PROXYHOST"] = proxy.Host;
+                    env["PROXYPORT"] = proxy.IsDefaultPort ? (proxy.Scheme.ToLowerInvariant() == "https" ? "443" : "80") : proxy.Port.ToString();
+                    if (HostContext.WebProxy.HttpProxyUsername != null ||
+                        HostContext.WebProxy.HttpsProxyUsername != null)
+                    {
+                        env["PROXYUSERNAME"] = HostContext.WebProxy.HttpProxyUsername ?? HostContext.WebProxy.HttpsProxyUsername;
+                        env["PROXYPASSWORD"] = HostContext.WebProxy.HttpProxyPassword ?? HostContext.WebProxy.HttpsProxyPassword;
+                    }
+                    else
+                    {
+                        env["PROXYUSERNAME"] = "";
+                        env["PROXYPASSWORD"] = "";
+                    }
+                }
+                else
+                {
+                    env["PROXYHOST"] = "";
+                    env["PROXYPORT"] = "";
+                    env["PROXYUSERNAME"] = "";
+                    env["PROXYPASSWORD"] = "";
+                }
+
+                if (extraCA)
+                {
+                    env["NODE_EXTRA_CA_CERTS"] = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Root), "download_ca_cert.pem");
+                }
+
+                using (var processInvoker = HostContext.CreateService<IProcessInvoker>())
+                {
+                    processInvoker.OutputDataReceived += new EventHandler<ProcessDataReceivedEventArgs>((sender, args) =>
+                    {
+                        if (!string.IsNullOrEmpty(args.Data))
+                        {
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} [STDOUT] {args.Data}");
+                        }
+                    });
+
+                    processInvoker.ErrorDataReceived += new EventHandler<ProcessDataReceivedEventArgs>((sender, args) =>
+                    {
+                        if (!string.IsNullOrEmpty(args.Data))
+                        {
+                            result.Logs.Add($"{DateTime.UtcNow.ToString("O")} [STDERR] {args.Data}");
+                        }
+                    });
+
+                    var makeWebRequestScript = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Bin), "checkScripts", "makeWebRequest.js");
+                    var node12 = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Externals), "node12", "bin", $"node{IOUtil.ExeExtension}");
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} Run '{node12} \"{makeWebRequestScript}\"' ");
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} {StringUtil.ConvertToJson(env)}");
+                    await processInvoker.ExecuteAsync(
+                        HostContext.GetDirectory(WellKnownDirectory.Root),
+                        node12,
+                        $"\"{makeWebRequestScript}\"",
+                        env,
+                        true,
+                        CancellationToken.None);
+                }
+
+                result.Pass = true;
+            }
+            catch (Exception ex)
+            {
+                result.Pass = false;
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Make https request to {url} using node.js failed with error: {ex}");
+                if (result.Logs.Any(x => x.Contains("UNABLE_TO_VERIFY_LEAF_SIGNATURE") ||
+                                         x.Contains("UNABLE_TO_GET_ISSUER_CERT_LOCALLY") ||
+                                         x.Contains("SELF_SIGNED_CERT_IN_CHAIN")))
+                {
+                    result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****     Https request failed due to SSL cert issue.");
+                    result.SslError = true;
+                }
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ****                                                                                                       ****");
+                result.Logs.Add($"{DateTime.UtcNow.ToString("O")} ***************************************************************************************************************");
+            }
+
+            return result;
+        }
+    }
+}

src/Runner.Listener/CommandSettings.cs

@@ -27,6 +27,7 @@ namespace GitHub.Runner.Listener
 
         private readonly string[] validFlags =
         {
+            Constants.Runner.CommandLine.Flags.Check,
             Constants.Runner.CommandLine.Flags.Commit,
             Constants.Runner.CommandLine.Flags.Help,
             Constants.Runner.CommandLine.Flags.Replace,
@@ -60,6 +61,7 @@ namespace GitHub.Runner.Listener
         public bool Warmup => TestCommand(Constants.Runner.CommandLine.Commands.Warmup);
 
         // Flags.
+        public bool Check => TestFlag(Constants.Runner.CommandLine.Flags.Check);
         public bool Commit => TestFlag(Constants.Runner.CommandLine.Flags.Commit);
         public bool Help => TestFlag(Constants.Runner.CommandLine.Flags.Help);
         public bool Unattended => TestFlag(Constants.Runner.CommandLine.Flags.Unattended);
@@ -188,10 +190,21 @@ namespace GitHub.Runner.Listener
                 validator: Validators.NonEmptyValidator);
         }
 
-        public string GetGitHubPersonalAccessToken()
+        public string GetGitHubPersonalAccessToken(bool required = false)
+        {
+            if (required)
+            {
+                return GetArgOrPrompt(
+                    name: Constants.Runner.CommandLine.Args.PAT,
+                    description: "What is your GitHub personal access token?",
+                    defaultValue: string.Empty,
+                    validator: Validators.NonEmptyValidator);
+            }
+            else
             {
                 return GetArg(name: Constants.Runner.CommandLine.Args.PAT);
             }
+        }
 
         public string GetRunnerRegisterToken()
         {

src/Runner.Listener/Configuration/ConfigurationManager.cs

@@ -117,7 +117,7 @@ namespace GitHub.Runner.Listener.Configuration
                 try
                 {
                     // Determine the service deployment type based on connection data. (Hosted/OnPremises)
-                    runnerSettings.IsHostedServer = runnerSettings.GitHubUrl == null || IsHostedServer(new UriBuilder(runnerSettings.GitHubUrl));
+                    runnerSettings.IsHostedServer = runnerSettings.GitHubUrl == null || UrlUtil.IsHostedServer(new UriBuilder(runnerSettings.GitHubUrl));
 
                     // Warn if the Actions server url and GHES server url has different Host
                     if (!runnerSettings.IsHostedServer)
@@ -508,13 +508,6 @@ namespace GitHub.Runner.Listener.Configuration
             return agent;
         }
 
-        private bool IsHostedServer(UriBuilder gitHubUrl)
-        {
-            return string.Equals(gitHubUrl.Host, "github.com", StringComparison.OrdinalIgnoreCase) ||
-                string.Equals(gitHubUrl.Host, "www.github.com", StringComparison.OrdinalIgnoreCase) ||
-                string.Equals(gitHubUrl.Host, "github.localhost", StringComparison.OrdinalIgnoreCase);
-        }
-
         private async Task<string> GetRunnerTokenAsync(CommandSettings command, string githubUrl, string tokenType)
         {
             var githubPAT = command.GetGitHubPersonalAccessToken();
@@ -551,7 +544,7 @@ namespace GitHub.Runner.Listener.Configuration
             if (path.Length == 1)
             {
                 // org runner
-                if (IsHostedServer(gitHubUrlBuilder))
+                if (UrlUtil.IsHostedServer(gitHubUrlBuilder))
                 {
                     githubApiUrl = $"{gitHubUrlBuilder.Scheme}://api.{gitHubUrlBuilder.Host}/orgs/{path[0]}/actions/runners/{tokenType}-token";
                 }
@@ -569,7 +562,7 @@ namespace GitHub.Runner.Listener.Configuration
                     repoScope = "";
                 }
 
-                if (IsHostedServer(gitHubUrlBuilder))
+                if (UrlUtil.IsHostedServer(gitHubUrlBuilder))
                 {
                     githubApiUrl = $"{gitHubUrlBuilder.Scheme}://api.{gitHubUrlBuilder.Host}/{repoScope}{path[0]}/{path[1]}/actions/runners/{tokenType}-token";
                 }
@@ -615,7 +608,7 @@ namespace GitHub.Runner.Listener.Configuration
         {
             var githubApiUrl = "";
             var gitHubUrlBuilder = new UriBuilder(githubUrl);
-            if (IsHostedServer(gitHubUrlBuilder))
+            if (UrlUtil.IsHostedServer(gitHubUrlBuilder))
             {
                 githubApiUrl = $"{gitHubUrlBuilder.Scheme}://api.{gitHubUrlBuilder.Host}/actions/runner-registration";
             }

src/Runner.Listener/Runner.cs

@@ -1,6 +1,5 @@
 using GitHub.DistributedTask.WebApi;
 using GitHub.Runner.Listener.Configuration;
-using GitHub.Runner.Common.Util;
 using System;
 using System.Threading;
 using System.Threading.Tasks;
@@ -11,6 +10,8 @@ using System.Reflection;
 using System.Runtime.CompilerServices;
 using GitHub.Runner.Common;
 using GitHub.Runner.Sdk;
+using System.Linq;
+using GitHub.Runner.Listener.Check;
 
 namespace GitHub.Runner.Listener
 {
@@ -72,6 +73,46 @@ namespace GitHub.Runner.Listener
                     return Constants.Runner.ReturnCode.Success;
                 }
 
+                if (command.Check)
+                {
+                    var url = command.GetUrl();
+                    var pat = command.GetGitHubPersonalAccessToken(required: true);
+                    var checkExtensions = HostContext.GetService<IExtensionManager>().GetExtensions<ICheckExtension>();
+                    var sortedChecks = checkExtensions.OrderBy(x => x.Order);
+                    foreach (var check in sortedChecks)
+                    {
+                        _term.WriteLine($"**********************************************************************************************************************");
+                        _term.WriteLine($"**  Check:               {check.CheckName}");
+                        _term.WriteLine($"**  Description:         {check.CheckDescription}");
+                        _term.WriteLine($"**********************************************************************************************************************");
+                        var result = await check.RunCheck(url, pat);
+                        if (!result)
+                        {
+                            _term.WriteLine($"**                                                                                                                  **");
+                            _term.WriteLine($"**                                            F A I L                                                               **");
+                            _term.WriteLine($"**                                                                                                                  **");
+                            _term.WriteLine($"**********************************************************************************************************************");
+                            _term.WriteLine($"** Log: {check.CheckLog}");
+                            _term.WriteLine($"** Help Doc: {check.HelpLink}");
+                            _term.WriteLine($"**********************************************************************************************************************");
+                        }
+                        else
+                        {
+                            _term.WriteLine($"**                                                                                                                  **");
+                            _term.WriteLine($"**                                            P A S S                                                               **");
+                            _term.WriteLine($"**                                                                                                                  **");
+                            _term.WriteLine($"**********************************************************************************************************************");
+                            _term.WriteLine($"** Log: {check.CheckLog}");
+                            _term.WriteLine($"**********************************************************************************************************************");
+                        }
+
+                        _term.WriteLine();
+                        _term.WriteLine();
+                    }
+
+                    return Constants.Runner.ReturnCode.Success;
+                }
+
                 // Configure runner prompt for args if not supplied
                 // Unattended configure mode will not prompt for args if not supplied and error on any missing or invalid value.
                 if (command.Configure)

src/Runner.Sdk/Util/UrlUtil.cs

@@ -4,6 +4,13 @@ namespace GitHub.Runner.Sdk
 {
     public static class UrlUtil
     {
+        public static bool IsHostedServer(UriBuilder gitHubUrl)
+        {
+            return string.Equals(gitHubUrl.Host, "github.com", StringComparison.OrdinalIgnoreCase) ||
+                string.Equals(gitHubUrl.Host, "www.github.com", StringComparison.OrdinalIgnoreCase) ||
+                string.Equals(gitHubUrl.Host, "github.localhost", StringComparison.OrdinalIgnoreCase);
+        }
+
         public static Uri GetCredentialEmbeddedUrl(Uri baseUrl, string username, string password)
         {
             ArgUtil.NotNull(baseUrl, nameof(baseUrl));

src/Test/L0/ServiceInterfacesL0.cs

@@ -1,4 +1,5 @@
 using GitHub.Runner.Listener;
+using GitHub.Runner.Listener.Check;
 using GitHub.Runner.Listener.Configuration;
 using GitHub.Runner.Worker;
 using GitHub.Runner.Worker.Handlers;
@@ -21,7 +22,8 @@ namespace GitHub.Runner.Common.Tests
             // Otherwise, the interface needs to whitelisted.
             var whitelist = new[]
             {
-                typeof(ICredentialProvider)
+                typeof(ICredentialProvider),
+                typeof(ICheckExtension),
             };
             Validate(
                 assembly: typeof(IMessageListener).GetTypeInfo().Assembly,
@@ -85,7 +87,8 @@ namespace GitHub.Runner.Common.Tests
                     continue;
                 }
 
-                if (interfaceTypeInfo.FullName.Contains("IConverter")){
+                if (interfaceTypeInfo.FullName.Contains("IConverter"))
+                {
                     continue;
                 }