Lifecycle Overview · Request Lifecycle in NestJS | NestJS

Lifecycle Overview

The Journey of One Request

Every request passes through the same stages in a fixed order. Knowing this order tells you where to put each piece of logic.

Incoming request  POST /api/orders
        |
        v
 1. Middleware            logging, request id, raw body, cookies      (Express-level)
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        v
 2. Guards                is the user logged in? allowed?             -> 401 / 403
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        v
 3. Interceptors (before) start timer, check cache
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        v
 4. Pipes                 validate and transform @Body/@Param/@Query  -> 400
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        v
 5. Controller handler -> Service -> Database
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        v
 6. Interceptors (after)  wrap/map the response, log time
        |
        v
 Response sent

 Any exception thrown in steps 2-6  -->  7. Exception filters  -->  error response

Which Tool for Which Job

Stage	Interface	Knows the handler?	Typical use
Middleware	`NestMiddleware`	No	Logging, CORS, helmet, request id
Guard	`CanActivate`	Yes (`ExecutionContext`)	Authentication, roles, feature flags
Interceptor	`NestInterceptor`	Yes	Timing, response shape, caching, timeouts
Pipe	`PipeTransform`	Only the argument	Validation, type conversion
Exception filter	`ExceptionFilter`	Yes (`ArgumentsHost`)	Error response format, error logging

Note: Guards run after all middleware but before any interceptor or pipe. So an unauthenticated request never reaches validation: it gets 401, not 400.