fail to link redis container to node.js container in docker

Question

I had deployed a simple redis based nodejs application on the digital ocean cloud.

Here is the node.js app.

var express = require('express');
var app = express();   
app.get('/', function(req, res){
  res.send('hello world');
});
app.set('trust proxy', 'loopback') 
app.listen(3000);

var redisClient = require('redis').createClient(6379,'localhost');
redisClient.on('connect',function(err){
   console.log('connect');
})

In order to deploy the application, I used one node.js container and one redis container respectively,and linked node.js container with redis container.

The redis container could be obtained by

docker run -d --name redis -p 6379:6379 dockerfile/redis

and the node.js container is based on google/nodejs, in which Dockerfile is simply as

FROM google/nodejs
WORKDIR   /src
EXPOSE  3000
CMD ["/bin/bash"]

my node.js image is named as nodejs and built by

docker build -t nodejs Dockerfile_path

and the container is run by copying my host applications files to the src folder in the container and linking the existing redis container

docker run -it --rm -p 8080:3000 --name app -v node_project_path:/src --link redis:redis nodejs

finally I got into the container successfully, then installed the npm modules by npm install and then start the application by node app.js.

But I got a error saying:

Error: Redis connection to localhost:6379 failed - connect ECONNREFUSED

As redis container is exposed to 6379, and my nodejs container is linking to redis container. in my node.js app, connecting to localhost redis server with port 6379 is supposed to be ok, why in fact it is not working at all

Answer 1

When you link the redis container to the node container, docker will already modify the hosts file for you

You should then be able to connect to the redis container via:

var redisClient = require('redis').createClient(6379,'redis'); // 'redis' is alias for the link -> what's in the hosts file.

From: https://docs.docker.com/userguide/dockerlinks/

$ sudo docker run -d -P --name web --link db:db training/webapp python app.py

This will link the new web container with the db container you created earlier. The --link flag takes the form:

--link name:alias

Where name is the name of the container we're linking to and alias is an alias for the link name. You'll see how that alias gets used shortly.