Add health check for Docker image

Dockerfile

@@ -17,6 +17,8 @@ RUN set -ex \
 
 FROM alpine
 
+ENV PUSHBITS_HTTP_PORT="8080"
+
 EXPOSE 8080
 
 WORKDIR /app
@@ -31,4 +33,6 @@ RUN set -ex \
 
 USER 1000
 
+HEALTHCHECK --interval=30s --timeout=5s --start-period=5s CMD curl --fail http://localhost:$PUSHBITS_HTTP_PORT/health || exit 1
+
 ENTRYPOINT ["./run"]

api/health.go

@@ -0,0 +1,22 @@
+package api
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+// HealthHandler holds information for processing requests about the server's health.
+type HealthHandler struct {
+	DB Database
+}
+
+// Health returns the health status of the server.
+func (h *HealthHandler) Health(ctx *gin.Context) {
+	if err := h.DB.Health(); err != nil {
+		ctx.AbortWithError(http.StatusInternalServerError, err)
+		return
+	}
+
+	ctx.JSON(http.StatusOK, gin.H{})
+}

api/interfaces.go

@@ -6,6 +6,8 @@ import (
 
 // The Database interface for encapsulating database access.
 type Database interface {
+	Health() error
+
 	CreateApplication(application *model.Application) error
 	DeleteApplication(application *model.Application) error
 	GetApplicationByID(ID uint) (*model.Application, error)

database/health.go

@@ -0,0 +1,6 @@
+package database
+
+// Health reports the status of the database connection.
+func (d *Database) Health() error {
+	return d.sqldb.Ping()
+}

router/router.go

@@ -24,6 +24,7 @@ func Create(debug bool, cm *credentials.Manager, db *database.Database, dp *disp
 	auth := authentication.Authenticator{DB: db}
 
 	applicationHandler := api.ApplicationHandler{DB: db, DP: dp}
+	healthHandler := api.HealthHandler{DB: db}
 	notificationHandler := api.NotificationHandler{DB: db, DP: dp}
 	userHandler := api.UserHandler{AH: &applicationHandler, CM: cm, DB: db, DP: dp}
 
@@ -42,6 +43,8 @@ func Create(debug bool, cm *credentials.Manager, db *database.Database, dp *disp
 		applicationGroup.PUT("/:id", api.RequireIDInURI(), applicationHandler.UpdateApplication)
 	}
 
+	r.GET("/health", healthHandler.Health)
+
 	r.POST("/message", auth.RequireApplicationToken(), notificationHandler.CreateNotification)
 
 	userGroup := r.Group("/user")