Redis connection failure with Docker compose files - docker

Question

I'm working with a docker-compose file from an open-source repo. Notably, it's missing the version and services keys, but it still works (up until now, I have not seen a compose file without these keys).
redis:
image: redis
ports:
- '6379'
app:
build: .
environment:
- LOG_LEVEL='debug'
links:
- redis
docker-compose up starts everything up and the app is able to talk to redis via 127.0.0.1:6379.
However, when I add the version and services keys back in, connections to redis are refused:
version: '3'
services:
redis:
image: redis
ports:
- '6379'
app:
build: .
environment:
- LOG_LEVEL='debug'
links:
- redis
Which results in:
[Wed Jan 03 2018 20:51:58 GMT+0000 (UTC)] ERROR { Error: Redis connection to 127.0.0.1:6379 failed - connect ECONNREFUSED 127.0.0.1:6379
at Object.exports._errnoException (util.js:896:11)
at exports._exceptionWithHostPort (util.js:919:20)
at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1073:14)
code: 'ECONNREFUSED',
errno: 'ECONNREFUSED',
syscall: 'connect',
address: '127.0.0.1',
port: 6379 }
Why does adding version: '3' and services: lead to failure to connect?

Answer 1

You don't need to specify the ports neither the links for services in the same network (compose file). You can use:
version: '3'
services:
redis:
image: redis
app:
build: .
environment:
- LOG_LEVEL='debug'
And then in your app code refer to redis just as 'redis:6379'. If you see the Dockerfile for the redis image you can see the port is already exposed at the end.

Answer 2

When you want to expose the service to a specific host port, in Docker Compose version 3 you should use this syntax:
ports:
- '6379:6379'
Check the docs here:
Either specify both ports (HOST:CONTAINER), or just the container port
(a random host port will be chosen).

Answer 3

This is what worked for me after having the same issue:
docker-compose.yml
version: "3"
services:
server:
...
depends_on:
- redis
redis:
image: redis
My redis config file:
const redis = require('redis');
const redisHost = 'redis';
const redisPort = '6379';
let client = redis.createClient(redisPort, redisHost);
client.on('connect', () => {
console.log(`Redis connected to ${redisHost}:${redisPort}`);
});
client.on('error', (err) => {
console.log(`Redis could not connect to ${redisHost}:${redisPort}: ${err}`);
});
module.exports = client;

Answer 4

The port might be in use. Either kill the container using it or restarting docker will release the port.