Connecting to RabbitMQ container with docker-compo

问题:

I want to run RabbitMQ in one container, and a worker process in another. The worker process needs to access RabbitMQ.

I'd like these to be managed through docker-compose.

This is my docker-compose.yml file so far:

version: "3"

services:

  rabbitmq:
    image: rabbitmq
    command: rabbitmq-server
    expose:
      - "5672"
      - "15672"

  worker:
    build: ./worker
    depends_on:
      - rabbitmq
    # Allow access to docker daemon
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock

So I've exposed the RabbitMQ ports. The worker process accesses RabbitMQ using the following URL:

amqp://guest:guest@rabbitmq:5672/

Which is what they use in the official tutorial, but localhost has been swapped for rabbitmq, since the the containers should be discoverable with a hostname identical to the container name:

By default Compose sets up a single network for your app. Each container for a service joins the default network and is both reachable by other containers on that network, and discoverable by them at a hostname identical to the container name.

Whenever I run this, I get an connection refused error:

Recreating ci_rabbitmq_1 ... done                                                                                                                                                    
Recreating ci_worker_1   ... done                                                                                                                                                    
Attaching to ci_rabbitmq_1, ci_worker_1                                                                                                                                              
worker_1    | dial tcp 127.0.0.1:5672: connect: connection refused                                                                                                                   
ci_worker_1 exited with code 1        

I find this interesting because it's using the IP 127.0.0.1 which (I think) is localhost, even though I specified rabbitmq as the hostname. I'm not an expert on docker networking, so maybe this is desired.

I'm happy to supply more information if needed!

---

Edit

There is an almost identical question here. I think I need to wait until rabbitmq is up and running before starting worker. I tried doing this with a healthcheck:

version: "2.1"

services:

  rabbitmq:
    image: rabbitmq
    command: rabbitmq-server
    expose:
      - "5672"
      - "15672"
    healthcheck:
      test: [ "CMD", "nc", "-z", "localhost", "5672" ]
      interval: 10s
      timeout: 10s
      retries: 5

  worker:
    build: .
    depends_on:
      rabbitmq:
        condition: service_healthy

(Note the different version). This doesn't work, however - it will always fail as not-healthy.

回答1:

Aha! I fixed it. @Ijaz was totally correct - the RabbitMQ service takes a while to start, and my worker tries to connect before it's running.

I tried using a delay, but this failed when the RabbitMQ took longer than usual.

This is also indicative of a larger architectural problem - what happens if the queuing service (RabbitMQ in my case) goes offline during production? Right now, my entire site fails. There needs to be some built-in redundancy and polling.

As described this this related answer, we can use healthchecks in docker-compose 3+:

version: "3"

services:

  rabbitmq:
    image: rabbitmq
    command: rabbitmq-server
    expose:
      - 5672
      - 15672
    healthcheck:
      test: [ "CMD", "nc", "-z", "localhost", "5672" ]
      interval: 5s
      timeout: 15s
      retries: 1

  worker:
    image: worker
    restart: on-failure
    depends_on:
      - rabbitmq

Now, the worker container will restart a few times while the rabbitmq container stays unhealthy. rabbitmq immediately becomes healthy when nc -z localhost 5672 succeeds - i.e. when the queuing is live!

回答2:

Maybe you dont need to expose/map the ports on the host if you are just accessing the service from another container.

From the documentation:

Expose Expose ports without publishing them to the host machine - they’ll only be accessible to linked services. Only the internal port can be specified.

expose:
 - "3000"
 - "8000"

So it should be like this:

version: "3"

services:

  rabbitmq:
    image: rabbitmq
    command: rabbitmq-server
    expose:
      - "5672"
      - "15672"

  worker:
    build: ./worker
    depends_on:
      - rabbitmq
    # Allow access to docker daemon
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock

also make sure to connect to rabitmq only when its ready to server on port.