How to connect to a Redis container using Docker Compose?

Question

This docker-compose.yml seems to work OK:

version: '3'
services:
  web:
    image: web-app
    command: bundle exec rackup
    ports:
     - "9292:9292"
    links:
      - redis
  redis:
    image: redis

Command:

docker build -t web-app .; docker-compose up

The Web App is expecting a REDIS_URL config. Web App Dockerfile:

ENV REDIS_URL redis:6379

It seems that the Web App cannot connect to the Redis:

Redis::CannotConnectError - Error connecting to Redis on 127.0.0.1:6379 (Errno::ECONNREFUSED):

So, what is the Redis URL for the Web App?

Do I need to expose the Redis port (6379)?

EDIT:

Thanks to @Andy Shinn, I see the redis url should be redis://6379.
Now I get Errno::EINVAL - Invalid argument - connect(2) for 0.0.24.235:6379. This may have to do with Redis v 3.2.8. I'll try another version and see if it works.

EDIT #2:

3.2.8 works fine with the app on my local machine, so that is not the issue.

Fannyfanon

Is redis running at that point? What happens if you start them all, and then restart the web after a bit -> that way you know that redis has been started. – Miscue

That error says the web service is trying to connect to redis at the local IP (127.0.0.1) and not the REDIS_URL which should be the redis DNS name from the link. What kind of application is this? Is it designed to use the REDIS_URL? It would be helpful to post a bit more about the application (Dockerfile, how it uses the REDIS_URL, etc). – Renae

Yes, it is configured to use the REDIS_URL. It's a Sinatra app. Other configs work, and production has a REDIS_URL. – Fannyfanon

@Miscue - Does not seem to be a timing issue. Redis starts before the web app. – Fannyfanon

Is 0.0.24.235 the IP it's attempting to reach now, or a copy/paste error? – Ernestineernesto

I'd also change link to depends_on, the link syntax is being phased out. – Ernestineernesto

@Ernestineernesto - That is the correct IP. I guess thats how links works...? I'll try depends_on. – Fannyfanon

That IP doesn't look right at all to me, if it was 10.0.24.235 it would make sense. Get the redis container ip from a docker inspect $redis_container_id (use docker ps to get the id) and compare to what the app is trying to use. – Ernestineernesto

Answer 1

The issue is that redis is "variable" that will be interpolated in the Dockerfile.

ENV REDIS_URL redis:6379

But the Redis URL should start with the literal redis.

So, the fix is updating the docker compose:

redis_db:
  image: redis:3.2.8

The desired config is:

REDIS_URL=redis://redis_db:6379

Thanks to BMitch and Andy Shinn for helping me figure this out.

Fannyfanon

FWIW, Mongo URL's can have the same issue because they start with mongodb://. – Fannyfanon

do you have any idea how REDIS_URL looks like if i set a password? – Expressive

@calvin redis://user:secret@localhost:6379/0?foo=bar&qux=baz – Cuboid

this saved a lot of time. thank you – Acarpous

Answer 2

I had the same issue. Resolved it by just specifying the network. So in your case it'll be

version: '3'
services:
  web:
    image: web-app
    command: bundle exec rackup
    ports:
     - "9292:9292"
    links:
      - redis
    networks:
      - mynetwork
  redis:
    image: redis
    networks:
      - mynetwork
networks:
  mynetwork:

And in this case redis host is redis

Thanksgiving

Answer 3

The create client config is updated in the new version

doc for the same https://github.com/redis/node-redis/blob/master/docs/client-configuration.md

Bohunk