Lifecycle hooks apa kang disediake NestJS?

Question

Accepted Answer

NestJS nyediake **lifecycle hooks** — metode sing didaksani kanggo njalanake kode ing momen spesifik ing lifecycle aplikasi utawa provider (inisialisasi lan shutdown). Penting banget kanggo setup (nyambung menyang resources) lan cleanup (nutup koneksi kanthi anggun).

## Hook utama

```ts
@Injectable()
export class DatabaseService
  implements OnModuleInit, OnApplicationShutdown {

async onModuleInit() {
    // runs once the host MODULE's dependencies are resolved → do INITIALIZATION
    await this.connect();         // e.g. open a database connection
  }

async onApplicationShutdown(signal: string) {
    // runs when the app is shutting down → do CLEANUP
    await this.disconnect();      // close connections, flush, release resources
  }
}
```

## Urutan lifecycle

```text
INITIALIZATION (startup):
  onModuleInit()          → after the module's providers are initialized
  onApplicationBootstrap()→ after ALL modules are initialized (whole app ready)

SHUTDOWN (graceful termination):
  onModuleDestroy()         → cleanup as modules are destroyed
  beforeApplicationShutdown() → before shutdown completes
  onApplicationShutdown(signal) → final shutdown (signal = SIGTERM, etc.)
```

## Kasuwan umum: layanan Prisma nyambung/pedhot

```ts
@Injectable()
export class PrismaService extends PrismaClient
  implements OnModuleInit, OnModuleDestroy {

async onModuleInit() {
    await this.$connect();        // connect on startup
  }
  async onModuleDestroy() {
    await this.$disconnect();      // disconnect on shutdown — clean release
  }
}
```

Ikine pola standar kanggo resources sing butuh setup/teardown eksplisit — nyambung ing `onModuleInit`, ngluwihi koneksi ing `onModuleDestroy`.

## Ngaktifake shutdown hooks

```ts
// shutdown hooks must be enabled explicitly
const app = await NestFactory.create(AppModule);
app.enableShutdownHooks();        // ❗ required for onApplicationShutdown etc. to fire
```

Shutdown hooks cuma ditindakake manawa ono manggon `enableShutdownHooks()` — gampang dilalekne, banjur cleanup ora tau kelakon.

## Kenapa graceful shutdown penting

```text
When the app receives SIGTERM (deploy, scale-down, container stop):
  ✗ Without shutdown hooks → connections left open, in-flight work dropped
  ✓ With shutdown hooks → close DB/Redis/queues cleanly, finish work → zero-downtime
```

## Dene iku penting

Lifecycle hooks penting banget kanggo ngurus resources kanthi bener ing aplikasi NestJS — nyediake papan sing pas kanggo nindakake **inisialisasi** (mbukak koneksi database/Redis, ngemot data, ndaftar karo layanan) lan, kang kritikal, **cleanup anggun** ing shutdown (nutup koneksi, ngebuwang buffer, ngrampungake karya sing isih mabur).

Ngerteni iku penting kanggo reliabilitas produksyon: **initialization hooks** (`onModuleInit`, `onApplicationBootstrap`) njamin setup kelakon ing wektu sing pas kepungkur dependensi siap, lan **shutdown hooks** (`onModuleDestroy`, `onApplicationShutdown`) ngaktifake **graceful shutdown** — kang penting ing deployment modern (kontainer/orchestrators ngirim SIGTERM terus-terusan ing saben deploy lan scaling, lan tanpa cleanup sing bener sampeyan bocor koneksi lan ilang request aktif, nglulumpukake zero-downtime deployments).

Pola standar nyambung ing `onModuleInit` lan pedhot ing `onModuleDestroy` (cth kanggo layanan Prisma/database) iku pengetahuan NestJS saben dina, lan wetere manawa kudu manggon `enableShutdownHooks()` (utawa shutdown hooks meneng-meneng ora pernah api) iku detalhe praktis, gampang dilalekne.

Nguasai lifecycle hooks iku bagean saking mbangun layanan NestJS sing tangguh, siap-produksyon sing nangani resources lan deployments kanthi bener.