Docker-compose - Redis at 0.0.0.0 instead of 127.0.0.1

Question

I havs migrated my Rails app (local dev machine) to Docker-Compose. All is working except the Worker Rails instance (batch) cannot connect to Redis.

Completed 500 Internal Server Error in 40ms (ActiveRecord: 2.3ms)

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

In my docker-compose.yml

redis:
  image: redis
  ports:
    - "6379:6379"

batch:
  build: .
  command: bundle exec rake environment resque:work QUEUE=*
  volumes:
    - .:/app
  links:
    - db
    - redis
  environment:
    - REDIS_URL=redis://redis:6379

I think the Redis instance is available via the IP of the Docker host.

$ docker-machine ls
NAME      ACTIVE   DRIVER       STATE     URL                       SWARM   DOCKER    ERRORS
default   *        virtualbox   Running   tcp://192.168.99.100:2376           v1.10.0

Accessing via 0.0.0.0 doesn't work

$ curl 0.0.0.0:6379 
curl: (7) Failed to connect to 0.0.0.0 port 6379: Connection refused

Accessing via the docker-machine IP I think works:

$ curl http://192.168.99.100:6379
-ERR wrong number of arguments for 'get' command
-ERR unknown command 'Host:'

EDIT

After installing redis-cli in the batch instance, I was able to hit the redis server using the 'redis' hostname. I think the problem is possibly in the Rails configuration itself.

First you shouldn't expect to curl or connect to any server via 0.0.0.0 as that isn't how TCP works. That address means "any" and only works when binding not connecting. Second you don't want to curl to Redis because it isn't an http server. — The Real Bill, Feb 12 '16 at 23:38
Thanks The Real Bill, so how would I troubleshoot these connectivity issues if not with curl? Cheers — port5432, Feb 12 '16 at 23:42

port5432 · Accepted Answer · 2016-02-13T11:16:12.190

5

Facepalm!!!

The docker containers were communicating just fine, the problem was I hadn't told Resque (the app using Redis) where to find it. Thank you to "The Real Bill" for pointing out I should be using docker-cli.

For anyone else using Docker and Resque, you need this in your config/initializers/resque.rb file:

Resque.redis = Redis.new(host: 'redis', port: 6379)
Resque.after_fork = Proc.new { ActiveRecord::Base.establish_connection }

edited Feb 13 '16 at 11:16

answered Feb 13 '16 at 11:03

port5432

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I'm doing same as you did @ardochhigh, but I'm using mongodb as database in separate container, so, would you please tell me what should be the configuration for monogdb or mongoid. – codemilan Jun 27 '16 at 06:04

score 2 · Answer 2 · answered Feb 11 '16 at 22:26

If you run

docker-compose run --rm batch env | grep REDIS

you will get the env variables that your container has (the link line in the compose will auto-generate some). Then all you need to do is look for one along the lines of _REDIS_1_PORT... and use the correct one. I have never had luck connecting my rails to another service in any other way. But luckily these env variables are always generated on start so they will be up to date even if the container IP happens to change between startups.

These env variables have been deprecated for a while and are removed in Docker 1.10. You should use the hostname to connect to other containers. — dnephin, Feb 12 '16 at 17:54

score 2 · Answer 3 · answered Feb 12 '16 at 17:55

2

You should use the hostname redis to connect to the service, although you may need to wait for redis to start.

answered Feb 12 '16 at 17:55

dnephin

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Thanks. Is that something different than in the code example in the original post? – port5432 Feb 12 '16 at 18:26
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The `REDIS_URL` variable looks correct, however it doesn't appear to be used, because the connection error says `127.0.0.1`. I think the application is ignoring that environment variable. – dnephin Feb 12 '16 at 20:27

Docker-compose - Redis at 0.0.0.0 instead of 127.0.0.1

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