Add custom health check endpoint

Signed-off-by: Povilas Vaitkus <povilas.vaitkus@hostinger.com>

Author: PovilasV1

README.md

@@ -99,6 +99,7 @@ If you are still using the legacy [Access scopes][access-scopes], the `https://w
 | `web.systemd-socket`                | No       |                           | Use systemd socket activation listeners instead of port listeners (Linux only).                                                                                                                   |
 | `web.stackdriver-telemetry-path`    | No       | `/metrics`                | Path under which to expose Stackdriver metrics.                                                                                                                                                   |
 | `web.telemetry-path`                | No       | `/metrics`                | Path under which to expose Prometheus metrics                                                                                                                                                     |
+| `web.health-check-path`             | No       | `/heath`                  | Path under which to expose health check                                                                                                                                                     |
 
 ### TLS and basic authentication
 

stackdriver_exporter.go

@@ -55,6 +55,10 @@ var (
 		"web.stackdriver-telemetry-path", "Path under which to expose Stackdriver metrics.",
 	).Default("/metrics").String()
 
+	healthCheckPath = kingpin.Flag(
+		"web.health-check-path", "Path under which to expose health check.",
+	).Default("/health").String()
+
 	projectID = kingpin.Flag(
 		"google.project-id", "DEPRECATED - Comma seperated list of Google Project IDs. Use 'google.project-ids' instead.",
 	).String()
@@ -275,6 +279,8 @@ func main() {
 	kingpin.HelpFlag.Short('h')
 	kingpin.Parse()
 
+	http.HandleFunc(*healthCheckPath, healthCheckHandler)
+
 	logger := promslog.New(promslogConfig)
 	if *projectID != "" {
 		logger.Warn("The google.project-id flag is deprecated and will be replaced by google.project-ids.")
@@ -432,3 +438,8 @@ func parseMetricExtraFilters() []collectors.MetricFilter {
 	}
 	return extraFilters
 }
+
+func healthCheckHandler(w http.ResponseWriter, r *http.Request) {
+    w.WriteHeader(http.StatusOK)
+    w.Write([]byte("OK"))
+}