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

github/fake/fake.go

@@ -32,7 +32,13 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 }
 
 // NewServer creates a fake server for running unit tests
-func NewServer() *httptest.Server {
+func NewServer(opts ...Option) *httptest.Server {
+	var responses FixedResponses
+
+	for _, o := range opts {
+		o(&responses)
+	}
+
 	routes := map[string]handler{
 		// For CreateRegistrationToken
 		"/repos/test/valid/actions/runners/registration-token": handler{
@@ -111,6 +117,9 @@ func NewServer() *httptest.Server {
 			Status: http.StatusBadRequest,
 			Body:   "",
 		},
+
+		// For auto-scaling based on the number of queued(pending) workflow runs
+		"/repos/test/valid/actions/runs": responses.listRepositoryWorkflowRuns.handler(),
 	}
 
 	mux := http.NewServeMux()

github/fake/options.go

@@ -0,0 +1,28 @@
+package fake
+
+type FixedResponses struct {
+	listRepositoryWorkflowRuns FixedResponse
+}
+
+type FixedResponse struct {
+	Status int
+	Body   string
+}
+
+func (r FixedResponse) handler() handler {
+	return handler{
+		Status: r.Status,
+		Body:   r.Body,
+	}
+}
+
+type Option func(responses *FixedResponses)
+
+func WithListRepositoryWorkflowRunsResponse(status int, body string) Option {
+	return func(r *FixedResponses) {
+		r.listRepositoryWorkflowRuns = FixedResponse{
+			Status: status,
+			Body:   body,
+		}
+	}
+}

github/github.go

@@ -27,8 +27,10 @@ func NewClient(appID, installationID int64, privateKeyPath string) (*Client, err
 		return nil, fmt.Errorf("authentication failed: %v", err)
 	}
 
+	gh := github.NewClient(&http.Client{Transport: tr})
+
 	return &Client{
-		Client:    github.NewClient(&http.Client{Transport: tr}),
+		Client:    gh,
 		regTokens: map[string]*github.RegistrationToken{},
 		mu:        sync.Mutex{},
 	}, nil