devapp: add healthz endpoint and configure k8s readiness probe

This will allow for zero-downtime deployments, which will be
important for when services start relying on the /owners endpoint.

Change-Id: I4671dbbbf473ba07dbab585222d12832c3193fac
Reviewed-on: https://go-review.googlesource.com/127036
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Author: andybons

devapp/deployment-prod.yaml

@@ -3,7 +3,7 @@ kind: Deployment
 metadata:
   name: devapp-deployment
 spec:
-  replicas: 1
+  replicas: 2
   template:
     metadata:
       labels:
@@ -17,6 +17,10 @@ spec:
         image: gcr.io/symbolic-datum-552/devapp:latest
         imagePullPolicy: Always
         command: ["/devapp", "-listen=:80", "-autocert-bucket=golang-devapp-autocert"]
+        readinessProbe:
+          httpGet:
+            path: /healthz
+            port: 80
         ports:
         - containerPort: 80
         - containerPort: 443

devapp/deployment-staging.yaml

@@ -3,7 +3,7 @@ kind: Deployment
 metadata:
   name: devapp-deployment
 spec:
-  replicas: 1
+  replicas: 2
   template:
     metadata:
       labels:
@@ -17,6 +17,10 @@ spec:
         image: gcr.io/go-dashboard-dev/devapp:latest
         imagePullPolicy: Always
         command: ["/devapp", "-listen=:80", "-autocert-bucket=golang-devapp-dev-autocert"]
+        readinessProbe:
+          httpGet:
+            path: /healthz
+            port: 80
         ports:
         - containerPort: 80
         - containerPort: 443

devapp/devapp.go

@@ -78,6 +78,10 @@ func main() {
 }
 
 func redirectHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path == "/healthz" {
+		handleHealthz(w, r)
+		return
+	}
 	if r.TLS != nil || r.Host == "" {
 		http.NotFound(w, r)
 		return

devapp/server.go

@@ -60,6 +60,7 @@ func newServer(mux *http.ServeMux, staticDir, templateDir string) *server {
 		userMapping: map[int]*maintner.GitHubUser{},
 	}
 	s.mux.Handle("/", http.FileServer(http.Dir(s.staticDir)))
+	s.mux.HandleFunc("/healthz", handleHealthz)
 	s.mux.HandleFunc("/favicon.ico", s.handleFavicon)
 	s.mux.HandleFunc("/release", s.withTemplate("/release.tmpl", s.handleRelease))
 	s.mux.HandleFunc("/reviews", s.withTemplate("/reviews.tmpl", s.handleReviews))
@@ -186,6 +187,11 @@ func (s *server) filteredHelpWantedIssues(pkgs ...string) []issueData {
 	return issues
 }
 
+func handleHealthz(w http.ResponseWriter, r *http.Request) {
+	w.WriteHeader(http.StatusOK)
+	w.Write([]byte("ok"))
+}
+
 func (s *server) handleFavicon(w http.ResponseWriter, r *http.Request) {
 	// Need to specify content type for consistent tests, without this it's
 	// determined from mime.types on the box the test is running on