X'inhi l-mudelli ta' reżiljenza li jipprotežu mikro-servizzi (circuit breaker, retry, timeout, bulkhead)?

Question

Accepted Answer

F'sistema distribwita, **kollox eventwalment jifal**. Il-mudelli ta' reżiljenza jwaqqfu l-falliment wieħed minn kaskada fi outage sħiħ.

## Il-mudelli ċentrali

- **Timeout** — qatt ma stennija għal dejjem għal risposta.
- **Retry** — erġa' pprova l-fallimenti temporanji, b'backoff + jitter.
- **Circuit breaker** — waqqaf li ssejjaħ servizz li jifal biex iħallih jirrepera.
- **Bulkhead** — izola l-risorsi sabiex dipendenza waħda ħamsa tiskond l-baqija.

## Eżempju ta' circuit breaker

```js
const breaker = new CircuitBreaker(callPaymentService, {
  timeout: 3000,                 // fail the call after 3s
  errorThresholdPercentage: 50,  // open if >50% of calls fail
  resetTimeout: 10000            // after 10s, try one request (half-open)
});
breaker.fallback(() => ({ status: 'queued' })); // graceful degradation
```

## Stati ta' circuit breaker

```text
CLOSED ──(failures exceed threshold)──▶ OPEN
  ▲                                       │ (after resetTimeout)
  │ (trial succeeds)                       ▼
  └────────────── HALF-OPEN ◀──────────────┘
                (one trial request)
```

## Bulkhead

```text
[ pool A: 10 threads ]  → payment calls
[ pool B: 10 threads ]  → search calls
If search hangs, it drains pool B only — payments keep working.
```

## Inqantra

**Retries mingħajr backoff** jammifikaw il-load fuq servizz li diġà qed itkompla (storm ta' retry). Dejjem żid backoff, jitter, u kap ta' retry.

## Għaliex dan huwa importanti

Dawn il-mudelli huma dawk li jduru falliment inevitabbli ta' servizz wieħed f'feature degraded minflok outage situs-wes.

Huma jaħdmu flimkien: timeouts bound stennija, circuit breaker jwaqqfu l-hammering ta' servizzi mejta, bulkheads iċ-ċirku tal-blast, u retries jirrepara minn blips — ittroka waħda u l-fallimenti għadhom kaskadi.