feat: automate health check with a written file

cmd/hp_healthcheck/hp_healthcheck.go

@@ -5,27 +5,37 @@ import (
 	"fmt"
 	"net/http"
 	"os"
+	"strings"
 	"time"
 )
 
-// hp_healthcheck pings the Headplane /healthz endpoint. It's invoked
-// from the Docker HEALTHCHECK directive, so it must work whether the
-// container is serving plain HTTP or has TLS termination enabled.
+// hp_healthcheck pings the Headplane healthz endpoint. It's invoked
+// from the Docker HEALTHCHECK directive inside the same container
+// as Headplane itself.
 //
-// Configuration (via env, all optional):
-//   - HEADPLANE_HEALTHCHECK_URL   full URL, takes precedence over the
-//     pieces below (default: http://localhost:3000/admin/healthz)
-//   - HEADPLANE_HEALTHCHECK_TLS   "true" to use https://
-//   - HEADPLANE_HEALTHCHECK_HOST  default: localhost
-//   - HEADPLANE_HEALTHCHECK_PORT  default: 3000
-//   - HEADPLANE_HEALTHCHECK_PATH  default: /admin/healthz
+// To stay fully zero-config, Headplane writes the exact URL the
+// healthcheck should hit — scheme, port, and basename included — to
+// listenFile when it starts accepting connections (see
+// runtime/http.ts and app/server/main.ts). This binary just reads
+// that file and GETs the URL verbatim. No env vars, no YAML
+// parsing, no path-joining, no compile-time knowledge of the
+// basename.
+//
+// If the file is missing (e.g. the server hasn't finished booting
+// on the very first probe, or this is an old image being run with
+// a new healthcheck) we fall back to the historical default.
+const (
+	listenFile = "/tmp/headplane-listen"
+	defaultURL = "http://localhost:3000/admin/healthz"
+)
+
 func main() {
-	url := healthcheckURL()
+	url := readListenFile()
 
 	client := http.Client{
 		Timeout: 5 * time.Second,
 		Transport: &http.Transport{
-			// We just care that the server is alive and with us
+			// Self-signed certs are normal for in-process TLS termination
 			TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
 		},
 	}
@@ -43,33 +53,16 @@ func main() {
 	}
 
 	fmt.Println("Health check passed.")
-	os.Exit(0)
 }
 
-func healthcheckURL() string {
-	if v := os.Getenv("HEADPLANE_HEALTHCHECK_URL"); v != "" {
-		return v
+func readListenFile() string {
+	data, err := os.ReadFile(listenFile)
+	if err != nil {
+		return defaultURL
 	}
-
-	scheme := "http"
-	if os.Getenv("HEADPLANE_HEALTHCHECK_TLS") == "true" {
-		scheme = "https"
+	url := strings.TrimSpace(string(data))
+	if url == "" {
+		return defaultURL
 	}
-
-	host := os.Getenv("HEADPLANE_HEALTHCHECK_HOST")
-	if host == "" {
-		host = "localhost"
-	}
-
-	port := os.Getenv("HEADPLANE_HEALTHCHECK_PORT")
-	if port == "" {
-		port = "3000"
-	}
-
-	path := os.Getenv("HEADPLANE_HEALTHCHECK_PATH")
-	if path == "" {
-		path = "/admin/healthz"
-	}
-
-	return fmt.Sprintf("%s://%s:%s%s", scheme, host, port, path)
+	return url
 }