feat: forward healthcheck to underlying process

Signed-off-by: thomasgouveia <gouveia.thomas@outlook.fr>

health.go

@@ -2,12 +2,20 @@ package main
 
 import "net/http"
 
-func healthHandler(w http.ResponseWriter, r *http.Request) {
-	// Currently we don't have any health probes implemented.
-	// We can return by default an HTTP 200 response.
-	// But in a future version, we will need to define how our agent
-	// can be marked as ready by the system to be able to trigger functions.
-	JSONResponse(w, &HealthResponse{
-		Status: "UP",
-	})
+func healthHandler(downstreamUrl string) func(w http.ResponseWriter, r *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		// Perform healthcheck on the downstream URL
+		// If an error is returned or the status code is not 200, we consider
+		// for now that the downstream is not healthy
+		if res, err := http.Get(downstreamUrl); err != nil || res.StatusCode != 200 {
+			JSONResponseWithStatusCode(w, http.StatusServiceUnavailable, &HealthResponse{
+				Status: "DOWN",
+			})
+			return
+		}
+
+		JSONResponse(w, &HealthResponse{
+			Status: "UP",
+		})
+	}
 }

helpers.go

@@ -13,13 +13,18 @@ func prettyJson(b []byte) []byte {
 }
 
 func JSONResponse(w http.ResponseWriter, data interface{}) {
+	JSONResponseWithStatusCode(w, http.StatusOK, data)
+}
+
+func JSONResponseWithStatusCode(w http.ResponseWriter, status int, data interface{}) {
 	body, err := json.Marshal(data)
 	if err != nil {
 		w.WriteHeader(http.StatusInternalServerError)
+		return
 	}
 
 	w.Header().Set("Content-Type", "application/json; charset=utf-8")
 	w.Header().Set("X-Content-Type-Options", "nosniff")
-	w.WriteHeader(http.StatusOK)
+	w.WriteHeader(status)
 	w.Write(prettyJson(body))
 }

main.go

@@ -215,7 +215,7 @@ func main() {
 
 	r := http.NewServeMux()
 	r.HandleFunc(rootEndpoint, handler(proxy))
-	r.HandleFunc(healthEndpoint, healthHandler)
+	r.HandleFunc(healthEndpoint, healthHandler(remote.String()))
 
 	server := &http.Server{
 		Addr:    fmt.Sprintf("0.0.0.0:%d", cfg.Server.Port),