feat: Repository-wide RunnerDeployment Autoscaling (#57)

* feat: Repository-wide RunnerDeployment Autoscaling

This adds `maxReplicas` and `minReplicas` to the RunnerDeploymentSpec. If and only if both fields are set, the controller computes and sets desired `replicas` automatically depending on the demand.

The number of demanded runner replicas is computed by `queued workflow runs + in_progress workflow runs` for the repository. The support for organizational runners is not included.

Ref https://github.com/summerwind/actions-runner-controller/issues/10

controllers/autoscaling.go

@@ -0,0 +1,92 @@
+package controllers
+
+import (
+	"context"
+	"fmt"
+	"github.com/summerwind/actions-runner-controller/api/v1alpha1"
+	"strings"
+)
+
+type NotSupported struct {
+}
+
+var _ error = NotSupported{}
+
+func (e NotSupported) Error() string {
+	return "Autoscaling is currently supported only when spec.repository is set"
+}
+
+func (r *RunnerDeploymentReconciler) determineDesiredReplicas(rd v1alpha1.RunnerDeployment) (*int, error) {
+	if rd.Spec.Replicas != nil {
+		return nil, fmt.Errorf("bug: determineDesiredReplicas should not be called for deplomeny with specific replicas")
+	} else if rd.Spec.MinReplicas == nil {
+		return nil, fmt.Errorf("runnerdeployment %s/%s is missing minReplicas", rd.Namespace, rd.Name)
+	} else if rd.Spec.MaxReplicas == nil {
+		return nil, fmt.Errorf("runnerdeployment %s/%s is missing maxReplicas", rd.Namespace, rd.Name)
+	}
+
+	var replicas int
+
+	repoID := rd.Spec.Template.Spec.Repository
+	if repoID == "" {
+		return nil, NotSupported{}
+	}
+
+	repo := strings.Split(repoID, "/")
+	user, repoName := repo[0], repo[1]
+	list, _, err := r.GitHubClient.Actions.ListRepositoryWorkflowRuns(context.TODO(), user, repoName, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	var total, inProgress, queued, completed, unknown int
+
+	for _, r := range list.WorkflowRuns {
+		total++
+
+		// In May 2020, there are only 3 statuses.
+		// Follow the below links for more details:
+		// - https://developer.github.com/v3/actions/workflow-runs/#list-repository-workflow-runs
+		// - https://developer.github.com/v3/checks/runs/#create-a-check-run
+		switch r.GetStatus() {
+		case "completed":
+			completed++
+		case "in_progress":
+			inProgress++
+		case "queued":
+			queued++
+		default:
+			unknown++
+		}
+	}
+
+	minReplicas := *rd.Spec.MinReplicas
+	maxReplicas := *rd.Spec.MaxReplicas
+	necessaryReplicas := queued + inProgress
+
+	var desiredReplicas int
+
+	if necessaryReplicas < minReplicas {
+		desiredReplicas = minReplicas
+	} else if necessaryReplicas > maxReplicas {
+		desiredReplicas = maxReplicas
+	} else {
+		desiredReplicas = necessaryReplicas
+	}
+
+	rd.Status.Replicas = &desiredReplicas
+	replicas = desiredReplicas
+
+	r.Log.V(1).Info(
+		"Calculated desired replicas",
+		"computed_replicas_desired", desiredReplicas,
+		"spec_replicas_min", minReplicas,
+		"spec_replicas_max", maxReplicas,
+		"workflow_runs_completed", completed,
+		"workflow_runs_in_progress", inProgress,
+		"workflow_runs_queued", queued,
+		"workflow_runs_unknown", unknown,
+	)
+
+	return &replicas, nil
+}