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

controllers/autoscaling.go

@@ -7,6 +7,7 @@ import (
 	"math"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/summerwind/actions-runner-controller/api/v1alpha1"
 	"sigs.k8s.io/controller-runtime/pkg/client"
@@ -19,6 +20,47 @@ const (
 	defaultScaleDownFactor    = 0.7
 )
 
+func getValueAvailableAt(now time.Time, from, to *time.Time, reservedValue int) *int {
+	if to != nil && now.After(*to) {
+		return nil
+	}
+
+	if from != nil && now.Before(*from) {
+		return nil
+	}
+
+	return &reservedValue
+}
+
+func (r *HorizontalRunnerAutoscalerReconciler) getDesiredReplicasFromCache(hra v1alpha1.HorizontalRunnerAutoscaler) *int {
+	var entry *v1alpha1.CacheEntry
+
+	for i := range hra.Status.CacheEntries {
+		ent := hra.Status.CacheEntries[i]
+
+		if ent.Key != v1alpha1.CacheEntryKeyDesiredReplicas {
+			continue
+		}
+
+		if !time.Now().Before(ent.ExpirationTime.Time) {
+			continue
+		}
+
+		entry = &ent
+
+		break
+	}
+
+	if entry != nil {
+		v := getValueAvailableAt(time.Now(), nil, &entry.ExpirationTime.Time, entry.Value)
+		if v != nil {
+			return v
+		}
+	}
+
+	return nil
+}
+
 func (r *HorizontalRunnerAutoscalerReconciler) determineDesiredReplicas(rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, error) {
 	if hra.Spec.MinReplicas == nil {
 		return nil, fmt.Errorf("horizontalrunnerautoscaler %s/%s is missing minReplicas", hra.Namespace, hra.Name)