How does the NestJS bootstrap sequence work?
NestJS bootstrap: NestFactory.create() scans the module graph, builds the DI container, instantiates all singletons, fires OnModuleInit hooks (depth-first), fires OnApplicationBootstrap hooks, then starts the HTTP server. On shutdown: OnModuleDestroy, BeforeApplicationShutdown, then OnApplicationShutdown fire in order.
Full bootstrap sequence:
- NestFactory.create(AppModule) is called.
- NestJS recursively scans the module graph — resolves all imports, providers, exports.
- The IoC container is built; all singleton providers are instantiated.
- OnModuleInit lifecycle hook fires for each module (depth-first order).
- OnApplicationBootstrap fires for each module.
- app.listen() starts the HTTP server — app is now ready to accept requests.
Implementing lifecycle hooks