EventPattern handler is not being triggered outside controllers - node.js

Question

I'm trying to setup a NestJS Hybrid Application that listens to a Redis service for events and triggers a handler in my code. I've defined a publisher that publishes events via ClientProxy.emit() as shown in the documentation.
EventPublisher.ts
#Injectable()
export class EventPublisher implements IEventPublisher {
constructor(#Inject('redisClient') private client: ClientProxy) {}
async publish<T extends IEvent = IEvent>(event: T) {
await this.client.emit('a', JSON.stringify({event})).toPromise();
}
}
I'm injecting my ClientProxy via my module class
const redisClient = ClientsModule.register([
{ name: 'redisClient', transport: Transport.REDIS, options: {
url: 'redis://localhost:6379'}
}
])
#Module({
imports: [
redisClient
],
... Other setups
})
export class FooModule {};
To listen to incoming events I created a microservice that uses redis as its transport.
main.ts
async function bootstrap() {
const app = await NestFactory.create(AppModule);
app.useGlobalPipes(new ValidationPipe());
const redisMicroservice = app.connectMicroservice<RedisOptions>({
transport: Transport.REDIS,
options: {
url: 'redis://localhost:6379'
}
})
await app.startAllMicroservicesAsync();
await app.listen(process.env.PORT || 3000);
}
This setup works fine as I am recieving the send data in my terminal when I subscirbe to 'a' using the redis-cli. I've tried defining eventhandlers on multiple classes in my code, but none of them are triggered when an event is emitted to Redis unless I create a handler that is located in a controller.
controller.ts
#EventPattern('a')
doSomething() {
console.log('success')
}
In the documentation I can't find any mention of eventhandlers having to be in a controller, but that seems to be the only location that triggers the handlers right now. Would anyone know what could be causing this? Any help is really appreciated.

Answer 1

I came to the same realisation yesterday. I tried to look for an explanation in the documentation, but as often with NestJS, I found none. #Decorators make it hard to investigate as they hide their logic.
It seems indeed that #EventPattern() will only be triggered if placed inside a #Controller(), but I have yet to understand why.