Add more extensive healthcheck support

- Add new cli argument: -healthcheck
- Add HEALTHCHECK instruction to Dockerfile
- Update Docker Compose examples

cli/health_check.go

@@ -0,0 +1,34 @@
+// Copyright 2021 Frédéric Guillot. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package cli // import "miniflux.app/cli"
+
+import (
+	"net/http"
+	"time"
+
+	"miniflux.app/config"
+	"miniflux.app/logger"
+)
+
+func doHealthCheck(healthCheckEndpoint string) {
+	if healthCheckEndpoint == "auto" {
+		healthCheckEndpoint = "http://" + config.Opts.ListenAddr() + config.Opts.BasePath() + "/healthcheck"
+	}
+
+	logger.Debug(`Executing health check on %s`, healthCheckEndpoint)
+
+	client := &http.Client{Timeout: 3 * time.Second}
+	resp, err := client.Get(healthCheckEndpoint)
+	if err != nil {
+		logger.Fatal(`Health check failure: %v`, err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != 200 {
+		logger.Fatal(`Health check failed with status code %d`, resp.StatusCode)
+	}
+
+	logger.Debug(`Health check is OK`)
+}