Celery workers unable to connect to redis on docker instances

Question

I have a dockerized setup running a Django app within which I use Celery tasks. Celery uses Redis as the broker.

Versioning:

• Docker ve

Answer 1

The issue for me was that all of the containers, including celery had a network argument specified. If this is the case the redis container must also have the same argument otherwise you will get this error. See below, the fix was adding 'networks':

  redis:
    image: redis:alpine
    ports:
      - '6379:6379'
    networks:
      - server

Answer 2

You may need to add the link and depends_on sections to your docker compose file, and then reference the containers by their hostname.

Updated docker-compose.yml:

version: '2.1'
services:
    db:
        image: postgres
    memcached:
        image: memcached
    redis:
        image: redis
        ports:
          - '6379:6379'
    backend-base:
        build:
            context: .
            dockerfile: backend/Dockerfile-base
        image: "/backend:base"
    backend:
        build:
            context: .
            dockerfile: backend/Dockerfile
        image: "/backend:${ENV:-local}"
        command: ./wait-for-it.sh db:5432 -- gunicorn backend.wsgi:application -b 0.0.0.0:8000 -k gevent -w 3
        ports:
            - 8000
        links:
            - db
            - redis
            - memcached
        depends_on:
            - db
            - redis
            - memcached
    celery:
        image: "/backend:${ENV:-local}"
        command: ./wait-for-it.sh db:5432 -- celery worker -E -B --loglevel=INFO --concurrency=1
        environment:
            C_FORCE_ROOT: "yes"
        links:
            - db
            - redis
            - memcached
        depends_on:
            - db
            - redis
            - memcached
    frontend-base:
        build:
            context: .
            dockerfile: frontend/Dockerfile-base
            args:
                NPM_REGISTRY: http://.view.build
                PACKAGE_INSTALLER: yarn
        image: "/frontend:base"
        links:
            - db
            - redis
            - memcached
        depends_on:
            - db
            - redis
            - memcached
    frontend:
        build:
            context: .
            dockerfile: frontend/Dockerfile
        image: "/frontend:${ENV:-local}"
        command: 'bash -c ''gulp'''
        working_dir: /app/user
        environment:
            PORT: 3000
        links:
            - db
            - redis
            - memcached
        depends_on:
            - db
            - redis
            - memcached

Then configure the urls to redis, postgres, memcached, etc. with:

• redis://redis:6379/0
• postgres://user:pass@db:5432/database

Answer 3

When you use docker-compose, you aren't going to be using localhost for inter-container communication, you would be using the compose-assigned hostname of the container. In this case, the hostname of your redis container is redis. The top level elements under services: are your default host names.

So for celery to connect to redis, you should try redis://redis:6379/0. Since the protocol and the service name are the same, I'll elaborate a little more: if you named your redis service "butter-pecan-redis" in your docker-compose, you would instead use redis://butter-pecan-redis:6379/0.

Also, docker-compose.dev.yml doesn't appear to have celery and redis on a common network, which might cause them not to be able to see each other. I believe they need to share at least one network in common to be able to resolve their respective host names.

Networking in docker-compose has an example in the first handful of paragraphs, with a docker-compose.yml to look at.