Kif timmplementa graceful shutdown?

Question

Accepted Answer

**Graceful shutdown** jfisser twaqqif server bis-sħiħ meta jirċievi signal ta' terminazzjoni — li twettaq ir-requests li għaddejjin, li tagħlaq il-konnessjonijiet (DB, eċċ.) u li释 ir-riżorsi — minflok li tqattilha b'mod subfissjoni u tieqaf ix-xogħol attiv. Huwa essenzjali għall-deplojamanturi mingħajr tħassil u r-reliability.

## Għaliex l-arresta baxxa hija problema

```text
Without graceful shutdown, when the process is killed (deploy, scale-down, crash):
  ✗ In-flight requests are dropped → users get errors
  ✗ DB transactions left incomplete
  ✗ Connections not closed cleanly → leaks/locks
```

Il-ħin tad-deplojamanturi u l-otomatiku skaling, il-proċessi huma migjuba kostanti — jagħmilha bis-sħiħ huwa dak li jagħmel id-deplojamanturi faċli.

## L-implimentazzjoni

```js
import http from "http";
const server = http.createServer(app);
server.listen(3000);

async function shutdown(signal) {
  console.log(`${signal} received — shutting down gracefully`);

// 1. Stop accepting NEW connections; finish existing ones
  server.close(async () => {
    // 2. This callback runs once all active requests have completed
    await db.end();            // close database pool
    await redis.quit();        // close other connections
    console.log("clean shutdown complete");
    process.exit(0);           // exit successfully
  });

// 3. Safety net: force-exit if cleanup hangs too long
  setTimeout(() => {
    console.error("forced shutdown — cleanup timed out");
    process.exit(1);
  }, 10_000).unref();
}

// Listen for termination signals
process.on("SIGTERM", () => shutdown("SIGTERM")); // sent by orchestrators (k8s, Docker)
process.on("SIGINT", () => shutdown("SIGINT"));   // Ctrl+C in dev
```

Is-sekwenza: aqbad is-signal → `server.close()` (waqqaf il-konnessjonijiet ġodda, ħarreġ dawk li jkunu eżistenti) → aghqal DB/Redis/riżorsi oħra → itlaq. **Timeout fallback** forza l-ħruġ jekk xi ħaġa tkun mispielda, sabiex konnessjoni maqbuża ma tistax tistampa l-waqqfien għal dejjem.

## Is-sinjali

```text
SIGTERM → the standard "please terminate" signal from orchestrators on deploy/scale-down
SIGINT  → Ctrl+C (development)
SIGKILL → cannot be caught (force kill) — graceful shutdown can't help here
```

## Fl-ambjenti kontenjorizzati

```text
Kubernetes/Docker send SIGTERM, wait a grace period (e.g. 30s), THEN SIGKILL.
Your app must finish within that window → keep the shutdown timeout shorter.
Readiness probes should mark the pod unready so the load balancer stops sending traffic.
```

## Għaliex huwa importanti

Graceful shutdown huwa dak li jippermettu **deplojamanturi mingħajr tħassil** u operazjoni affidabbli f'ambjenti moderni (speċjalment kontenjorizzati/orkestruiti), fejn il-proċessi huma migjuba u jibdew mill-ġdid kostanti.

Beduxha, kull deprojament jew tnaqqis tad-dimensjoni jerġa' l-requests attivi u għaddejjin risk ta' inkonżistenza tad-data.

L-implimentazzjoni tal-iskena catch-signal → stop-accepting → drain → close-resources → exit (b'safety net timeout) hija sinsla ta' servizzi Node lesti għall-produzzjoni u koinċidenza operazzjonali li spiss hija mijtuba imma importanti.