NestJS Case Studies & Practical Application 2

Question 1

A NestJS microservice needs to handle intermittent downstream failures gracefully. Which pattern combined with `@nestjs/axios` best implements retry logic?

Accepted Answer

Use RxJS `retry` operator on the HTTP observable

Answer

RxJS `retry` composes directly on observables returned by HttpService, enabling declarative retry logic without imperative loops.

Question 2

You need to run a NestJS background job every weekday at 9 AM UTC. Which decorator and cron expression are correct?

Accepted Answer

@Cron('0 9 * * 1-5') on a ScheduleModule method

Answer

`@Cron('0 9 * * 1-5')` means minute 0, hour 9, any day, any month, Mon-Fri — standard cron for weekday 9 AM.

Question 3

A team is building a multi-tenant SaaS app in NestJS. Each tenant's data must be isolated at the database level. What is the recommended approach using AsyncLocalStorage?

Accepted Answer

Store the tenant ID in AsyncLocalStorage inside request-scoped middleware and inject it into a custom TypeORM connection factory

Answer

AsyncLocalStorage propagates context across async calls within a request, letting a connection factory select the correct tenant schema without threading it through every function.

Question 4

Your NestJS REST API returns 200 for both success and business errors. A code review flags this. What is the idiomatic NestJS fix?

Accepted Answer

Throw built-in HttpExceptions (e.g., BadRequestException) and let the global exception filter map them to correct HTTP codes

Answer

NestJS's built-in exception layer translates HttpException subclasses to correct HTTP status codes automatically, keeping controllers clean.

Question 5

A NestJS app uses Passport JWT strategy. After deploying a new signing secret, existing valid tokens fail authentication. What went wrong?

Accepted Answer

The new secret was not propagated to JwtModule options, so verification fails against the old secret

Answer

JwtModule.register bakes the secret at startup; if the env variable changed without a restart, the old secret is still in use for verification.

NestJS Practice Test

NestJS Practice Test

NestJS Case Studies & Practical Application 2