fix(issue-9): No Dockerfile to build service

cmd/healthcheck/main.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+	"time"
+)
+
+func main() {
+	url := "http://127.0.0.1:8080/healthz"
+	if len(os.Args) > 1 {
+		url = os.Args[1]
+	}
+
+	client := &http.Client{Timeout: 3 * time.Second}
+	resp, err := client.Get(url)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "healthcheck error: %v\n", err)
+		os.Exit(1)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		fmt.Fprintf(os.Stderr, "healthcheck failed: status %s\n", resp.Status)
+		os.Exit(1)
+	}
+}