internal/worker: add health check endpoint

This will be used with GKE health checks. The health checks
hit "/" by default, which causes unnecessary work.

Change-Id: I6093e5985102153bbabeb19feebbae1a44d55a9f
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/254378
Reviewed-by: Julie Qiu <julie@golang.org>

2 files changed, 15 insertions, 0 deletions

diff --git a/internal/database/database.go b/internal/database/database.go
index fa82e6ce..bff5b08c 100644
--- a/internal/database/database.go
+++ b/internal/database/database.go
@@ -55,6 +55,10 @@ func New(db *sql.DB, instanceID string) *DB {
 	return &DB{db: db, instanceID: instanceID}
 }
 
+func (db *DB) Ping() error {
+	return db.db.Ping()
+}
+
 func (db *DB) InTransaction() bool {
 	return db.tx != nil
 }
diff --git a/internal/worker/server.go b/internal/worker/server.go
index 9622dbf3..3444beab 100644
--- a/internal/worker/server.go
+++ b/internal/worker/server.go
@@ -204,6 +204,9 @@ func (s *Server) Install(handle func(string, http.Handler)) {
 	// returns an HTML page displaying information about recent versions that were processed.
 	handle("/versions", http.HandlerFunc(s.handleHTMLPage(s.doVersionsPage)))
 
+	// Health check.
+	handle("/healthz", http.HandlerFunc(s.handleHealthCheck))
+
 	// returns an HTML page displaying the homepage.
 	handle("/", http.HandlerFunc(s.handleHTMLPage(s.doIndexPage)))
 }
@@ -521,6 +524,14 @@ func (s *Server) updateExperiment(w http.ResponseWriter, r *http.Request) error
 	return nil
 }
 
+func (s *Server) handleHealthCheck(w http.ResponseWriter, r *http.Request) {
+	if err := s.db.Underlying().Ping(); err != nil {
+		http.Error(w, fmt.Sprintf("DB ping failed: %v", err), http.StatusInternalServerError)
+		return
+	}
+	fmt.Fprintln(w, "OK")
+}
+
 // Parse the template for the status page.
 func parseTemplate(staticPath, filename template.TrustedSource) (*template.Template, error) {
 	if staticPath.String() == "" {