How do you handle errors in microservice request-response patterns and propagate them to the caller in NestJS?

Q: How do you handle errors in microservice request-response patterns and propagate them to the caller in NestJS?

// Microservice handler — throw RpcException for structured errors @MessagePattern({ cmd: 'get_user' }) async getUser(@Payload() data: { id: number }): Promise { const user = await this.usersService.findOne(data.id); if (!user) { throw new RpcException({ statusCode: 404, message: 'User not found' }); } return user; } // Global filter on the gateway — maps RpcException to HTTP response @Catch(RpcException) export class RpcExceptionFilter implements ExceptionFilter { catch(exception: RpcException, host: ArgumentsHost) { const error = exception.getError(); const ctx = host.switchToHttp(); const res = ctx.getResponse (); const status = typeof error === 'object' ? (error as any).statusCode ?? 500 : 500; const message = typeof error === 'object' ? (error as any).message : error; res.status(status).json({ statusCode: status, message }); } } // Caller — catch and remap errors in the Observable pipeline const user = await firstValueFrom( this.client.send ({ cmd: 'get_user' }, { id }).pipe( catchError(err => throwError(() => new NotFoundException(err.message))), ), ); RpcException is the correct exception class for microservice handlers — plain Error objects are not serialized properly. Pass an object to RpcException with statusCode and message for structured error payloads. The gateway must have a global RpcExceptionFilter to convert RpcException to HTTP responses. catchError() in the Observable pipeline intercepts errors from send() before they propagate as unhandled. throwError(() => new HttpException(...)) re-throws as an HTTP exception so the gateway's exception filters handle it.

Difficulty: 6/10

Exception Filters, HttpException, Microservice Transport

Throw RpcException on the microservice side to send structured errors back to the caller. On the API gateway or caller side, catch errors in the Observable pipeline with catchError() and rethrow as HTTP exceptions. Register a global RpcExceptionFilter to convert RpcException to HTTP responses on the gateway.

RpcException on service, filter and catchError on gateway

Error propagation rules:

1
RpcException is the correct exception class for microservice handlers — plain Error objects are not serialized properly.
2

How do you handle errors in microservice request-response patterns and propagate them to the caller in NestJS?

Difficulty: 6/10

Exception Filters, HttpException, Microservice Transport

Throw RpcException on the microservice side to send structured errors back to the caller. On the API gateway or caller side, catch errors in the Observable pipeline with catchError() and rethrow as HTTP exceptions. Register a global RpcExceptionFilter to convert RpcException to HTTP responses on the gateway.

RpcException on service, filter and catchError on gateway

Error propagation rules:

1
RpcException is the correct exception class for microservice handlers — plain Error objects are not serialized properly.
2

How do you handle errors in microservice request-response patterns and propagate them to the caller in NestJS?

How do you handle errors in microservice request-response patterns and propagate them to the caller in NestJS?

Scenario Questions

Follow-up Questions