add demo app

main.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+)
+
+func main() {
+	// Read from the environment, not baked in at build time — the Helm
+	// chart's deployment.env sets APP_VERSION from the same image tag
+	// updateHelmTag.groovy just bumped, so curling /version proves the
+	// whole CI/CD loop (build -> push -> tag-bump -> deploy) actually
+	// worked end to end, not just that "some" image is running.
+	version := os.Getenv("APP_VERSION")
+	if version == "" {
+		version = "dev"
+	}
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, "hello from demo-go-app, version %s\n", version)
+	})
+	http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		fmt.Fprintln(w, "ok")
+	})
+	http.HandleFunc("/version", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintln(w, version)
+	})
+
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "8080"
+	}
+	log.Printf("listening on :%s (version %s)", port, version)
+	log.Fatal(http.ListenAndServe(":"+port, nil))
+}