gRPC & Kafka

Preview — 3 of 10 questions

With the gRPC transport, how is a service method on a controller bound to a proto-defined RPC?

javascript

import { GrpcMethod } from '@nestjs/microservices';

@Controller()
export class HeroesController {
  @GrpcMethod('HeroesService', 'FindOne')
  findOne(data: { id: number }) {
    return heroes.find((h) => h.id === data.id);
  }
}

AUse @MessagePattern('Method')

BUse @GrpcMethod('ServiceName', 'MethodName') matching the service and rpc names in the .proto

CUse @EventPattern('Method')

DgRPC requires no decorator — names auto-bind by convention only

How does a NestJS gRPC handler implement server streaming back to the client?

javascript

import { GrpcStreamMethod } from '@nestjs/microservices';
import { Observable, Subject } from 'rxjs';

@GrpcStreamMethod('ChatService', 'Converse')
converse(messages$: Observable<ChatMsg>): Observable<ChatMsg> {
  const out$ = new Subject<ChatMsg>();
  messages$.subscribe({
    next: (m) => out$.next({ ...m, echoed: true }),
    complete: () => out$.complete(),
  });
  return out$.asObservable();
}

AReturn a plain array

BReturn an Observable (e.g. an RxJS Subject) whose emissions are streamed to the client until it completes

CCall res.write() like Express

DStreaming is unsupported in NestJS gRPC

In the Kafka transport, what role does the consumer.groupId play across multiple instances of a service?

javascript

ClientsModule.register([{
  name: 'KAFKA',
  transport: Transport.KAFKA,
  options: {
    client: { brokers: ['localhost:9092'] },
    consumer: { groupId: 'orders-consumer' }, // scale instances under same group
  },
}]);

AIt is cosmetic and has no effect

BEvery instance in the group receives every message

CInstances sharing a groupId form a consumer group; partitions are distributed among them so each message is processed by exactly one instance in the group

DIt controls the producer's topic name

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