feat: HorizontalRunnerAutoscaler Webhook server (#282)

* feat: HorizontalRunnerAutoscaler Webhook server

This introduces a Webhook server that responds GitHub `check_run`, `pull_request`, and `push` events by scaling up matched HorizontalRunnerAutoscaler by 1 replica. This allows you to immediately add "resource slack" for future GitHub Actions job runs, without waiting next sync period to add insufficient runners.

This feature is highly inspired by https://github.com/philips-labs/terraform-aws-github-runner. terraform-aws-github-runner can manage one set of runners per deployment, where actions-runner-controller with this feature can manage as many sets of runners as you declare with HorizontalRunnerAutoscaler and RunnerDeployment pairs.

On each GitHub event received, the webhook server queries repository-wide and organizational runners from the cluster and searches for the single target to scale up. The webhook server tries to match HorizontalRunnerAutoscaler.Spec.ScaleUpTriggers[].GitHubEvent.[CheckRun|Push|PullRequest] against the event and if it finds only one HRA, it is the scale target. If none or two or more targets are found for repository-wide runners, it does the same on organizational runners.

Changes:

* Fix integration test
* Update manifests
* chart: Add support for github webhook server
* dockerfile: Include github-webhook-server binary
* Do not import unversioned go-github
* Update README

cmd/githubwebhookserver/main.go

@@ -0,0 +1,169 @@
+/*
+Copyright 2021 The actions-runner-controller authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"net/http"
+	"os"
+	"sync"
+	"time"
+
+	actionsv1alpha1 "github.com/summerwind/actions-runner-controller/api/v1alpha1"
+	"github.com/summerwind/actions-runner-controller/controllers"
+	"k8s.io/apimachinery/pkg/runtime"
+	clientgoscheme "k8s.io/client-go/kubernetes/scheme"
+	_ "k8s.io/client-go/plugin/pkg/client/auth/exec"
+	_ "k8s.io/client-go/plugin/pkg/client/auth/gcp"
+	_ "k8s.io/client-go/plugin/pkg/client/auth/oidc"
+	ctrl "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/log/zap"
+	// +kubebuilder:scaffold:imports
+)
+
+var (
+	scheme   = runtime.NewScheme()
+	setupLog = ctrl.Log.WithName("setup")
+)
+
+func init() {
+	_ = clientgoscheme.AddToScheme(scheme)
+
+	_ = actionsv1alpha1.AddToScheme(scheme)
+	// +kubebuilder:scaffold:scheme
+}
+
+func main() {
+	var (
+		err error
+
+		webhookAddr string
+		metricsAddr string
+
+		// The secret token of the GitHub Webhook. See https://docs.github.com/en/developers/webhooks-and-events/securing-your-webhooks
+		webhookSecretToken string
+
+		watchNamespace string
+
+		enableLeaderElection bool
+		syncPeriod           time.Duration
+	)
+
+	webhookSecretToken = os.Getenv("GITHUB_WEBHOOK_SECRET_TOKEN")
+
+	flag.StringVar(&webhookAddr, "webhook-addr", ":8000", "The address the metric endpoint binds to.")
+	flag.StringVar(&metricsAddr, "metrics-addr", ":8080", "The address the metric endpoint binds to.")
+	flag.StringVar(&watchNamespace, "watch-namespace", "", "The namespace to watch for HorizontalRunnerAutoscaler's to scale on Webhook. Set to empty for letting it watch for all namespaces.")
+	flag.BoolVar(&enableLeaderElection, "enable-leader-election", false,
+		"Enable leader election for controller manager. Enabling this will ensure there is only one active controller manager.")
+	flag.DurationVar(&syncPeriod, "sync-period", 10*time.Minute, "Determines the minimum frequency at which K8s resources managed by this controller are reconciled. When you use autoscaling, set to a lower value like 10 minute, because this corresponds to the minimum time to react on demand change")
+	flag.Parse()
+
+	if webhookSecretToken == "" {
+		setupLog.Info("-webhook-secret-token is missing or empty. Create one following https://docs.github.com/en/developers/webhooks-and-events/securing-your-webhooks")
+	}
+
+	if watchNamespace == "" {
+		setupLog.Info("-watch-namespace is empty. HorizontalRunnerAutoscalers in all the namespaces are watched, cached, and considered as scale targets.")
+	} else {
+		setupLog.Info("-watch-namespace is %q. Only HorizontalRunnerAutoscalers in %q are watched, cached, and considered as scale targets.")
+	}
+
+	logger := zap.New(func(o *zap.Options) {
+		o.Development = true
+	})
+
+	ctrl.SetLogger(logger)
+
+	mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{
+		Scheme:             scheme,
+		SyncPeriod:         &syncPeriod,
+		LeaderElection:     enableLeaderElection,
+		Namespace:          watchNamespace,
+		MetricsBindAddress: metricsAddr,
+		Port:               9443,
+	})
+	if err != nil {
+		setupLog.Error(err, "unable to start manager")
+		os.Exit(1)
+	}
+
+	hraGitHubWebhook := &controllers.HorizontalRunnerAutoscalerGitHubWebhook{
+		Client:         mgr.GetClient(),
+		Log:            ctrl.Log.WithName("controllers").WithName("Runner"),
+		Recorder:       nil,
+		Scheme:         mgr.GetScheme(),
+		SecretKeyBytes: []byte(webhookSecretToken),
+		WatchNamespace: watchNamespace,
+	}
+
+	if err = hraGitHubWebhook.SetupWithManager(mgr); err != nil {
+		setupLog.Error(err, "unable to create controller", "controller", "Runner")
+		os.Exit(1)
+	}
+
+	var wg sync.WaitGroup
+
+	ctx, cancel := context.WithCancel(context.Background())
+
+	wg.Add(1)
+	go func() {
+		defer cancel()
+		defer wg.Done()
+
+		setupLog.Info("starting webhook server")
+		if err := mgr.Start(ctx.Done()); err != nil {
+			setupLog.Error(err, "problem running manager")
+			os.Exit(1)
+		}
+	}()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/", hraGitHubWebhook.Handle)
+
+	srv := http.Server{
+		Addr:    webhookAddr,
+		Handler: mux,
+	}
+
+	wg.Add(1)
+	go func() {
+		defer cancel()
+		defer wg.Done()
+
+		go func() {
+			<-ctx.Done()
+
+			srv.Shutdown(context.Background())
+		}()
+
+		if err := srv.ListenAndServe(); err != nil {
+			if !errors.Is(err, http.ErrServerClosed) {
+				setupLog.Error(err, "problem running http server")
+			}
+		}
+	}()
+
+	go func() {
+		<-ctrl.SetupSignalHandler()
+		cancel()
+	}()
+
+	wg.Wait()
+}