# OnApplicationShutdown

**Kind:** Interface

**Source:** [`packages/common/interfaces/hooks/on-application-shutdown.interface.ts`](https://github.com/nestjs/nest/blob/master/packages/common/interfaces/hooks/on-application-shutdown.interface.ts#L9)

**Part of:** [Common](subsystem-packages-common)

Interface defining method to respond to system signals (when application gets
shutdown by, e.g., SIGTERM)

`OnApplicationShutdown` is a lifecycle hook interface for providers that need to perform cleanup when the application is shutting down. Implement `onApplicationShutdown()` to respond to operating-system signals such as `SIGTERM` and release resources such as database connections, queues, or background workers.

## Diagram

```mermaid
graph LR
  Signal[OS signal: SIGTERM / SIGINT] --> App[Nest application]
  App --> Lifecycle[Shutdown lifecycle hooks]
  Lifecycle --> Hook[OnApplicationShutdown]
  Hook --> Cleanup[Release resources and cleanup]
```

## Usage

```ts
import { Injectable, OnApplicationShutdown } from '@nestjs/common';

@Injectable()
export class DatabaseService implements OnApplicationShutdown {
  async onApplicationShutdown(signal?: string) {
    console.log(`Application shutting down via ${signal ?? 'unknown signal'}`);

    // Close database connections, stop workers, flush telemetry, etc.
    await this.closeDatabaseConnection();
  }

  private async closeDatabaseConnection() {
    // Cleanup implementation
  }
}

// Enable shutdown hooks during application bootstrap:
// const app = await NestFactory.create(AppModule);
// app.enableShutdownHooks();
```

## AI Coding Instructions

- Implement `onApplicationShutdown(signal?: string)` in injectable providers that own resources requiring graceful cleanup.
- Enable shutdown hooks with `app.enableShutdownHooks()`; the hook is not invoked for OS signals unless shutdown hooks are enabled.
- Treat the optional `signal` parameter as informational, since shutdown can also be initiated programmatically.
- Make cleanup operations idempotent and safe to run during partial application initialization.
- Await asynchronous cleanup work so connections, queues, and telemetry are properly flushed before process exit.

## Used by

3 references from 3 files. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

### Imported by (3)

- `ServerGateway` — `integration/websockets/src/server.gateway.ts`:6
- `ClientsModule` — `packages/microservices/module/clients.module.ts`:17
- `callAppShutdownHook` — `packages/core/hooks/on-app-shutdown.hook.ts`:45