feat: correlate server errors and monitor application health

scripts/monitor.ts

@@ -0,0 +1,21 @@
+import { probeHealth, healthObserver } from "../src/ops/monitor";
+const target = new URL(process.env.MONITOR_URL || `http://127.0.0.1:${process.env.PORT ?? 3000}/api/health`);
+if (!["http:", "https:"].includes(target.protocol) || target.username || target.password) throw new Error("MONITOR_URL must be an HTTP(S) URL without credentials");
+const emit = (event: Record<string, unknown>) => console.log(JSON.stringify(event));
+if (process.argv.includes("--once")) {
+  const result = await probeHealth(target.href);
+  emit({ event: "health_probe", ...result });
+  process.exitCode = result.healthy ? 0 : 1;
+} else {
+  const observe = healthObserver(emit);
+  let running = false;
+  const check = async () => {
+    if (running) return;
+    running = true;
+    try { observe(await probeHealth(target.href)); } finally { running = false; }
+  };
+  await check();
+  const timer = setInterval(() => void check(), 60000);
+  const stop = () => { clearInterval(timer); process.exit(0); };
+  process.on("SIGTERM", stop); process.on("SIGINT", stop);
+}