What is the main.ts file in a NestJS application?

The main.ts file is the entry point of a NestJS application. It uses the NestFactory to bootstrap the application: const app = await NestFactory.create(AppModule);. This function creates the NestJS IoC container and compiles the module dependency graph. After creating the app instance, you configure global settings: app.useGlobalPipes(new ValidationPipe()), app.enableCors(), app.setGlobalPrefix('api'), Swagger setup. Then start listening: await app.listen(3000);. In production, you might read the port from process.env.PORT. The AppModule is the root module that imports all feature modules, making it the composition root of the application.