NestJS Lifecycle Events

Common Lifecycle Interfaces

Implement interfaces like OnModuleInit, OnApplicationBootstrap, OnModuleDestroy, and BeforeApplicationShutdown on providers. Nest calls them at well-defined times while booting or closing the app.

@Injectable()
export class PrismaService extends PrismaClient implements OnModuleInit, OnModuleDestroy {
  async onModuleInit() { await this.$connect(); }
  async onModuleDestroy() { await this.$disconnect(); }
}

Database clients commonly connect on init and disconnect on destroy to avoid leaked connections.

Hook Order (Simplified)

construct providers
-> onModuleInit
-> onApplicationBootstrap
(app running)
-> onModuleDestroy / beforeApplicationShutdown
-> onApplicationShutdown

• Use onModuleInit for per-module setup after DI is ready.
• Use onApplicationBootstrap when you need the whole app graph initialized.
• Enable shutdown hooks with app.enableShutdownHooks() for SIGTERM handling.
• Keep hooks idempotent and resilient—startup can be retried in containers.

Lifecycle Hooks Cheatsheet

Where to put startup/shutdown logic.

Graceful Shutdown

In Kubernetes, pods receive SIGTERM. Enabling Nest shutdown hooks lets you finish in-flight requests and close brokers cleanly before exit.

const app = await NestFactory.create(AppModule);
app.enableShutdownHooks();

Request-Scoped Providers

Request-scoped providers have different lifecycles. Prefer singleton providers for long-lived connections.

Common Mistakes

• Opening connections in constructors instead of onModuleInit.
• Forgetting shutdown hooks and leaking broker consumers on deploy.
• Doing heavy synchronous work in hooks and delaying boot health checks.
• Assuming hooks run in tests without initializing the Nest app context.

Key Takeaways

• Lifecycle interfaces hook providers into Nest boot/shutdown.
• Connect resources on init; release them on destroy.
• Enable shutdown hooks for graceful production deploys.
• Prefer singletons for long-lived connections.