docker-links

Docker Links Environment Parser

Docker has a feature where you can link containers together by name. For example, you start a redis-server in a docker container and expose the default redis port 6379:

$ docker run -p 6379 -d -name redis vagrant/redis-server

You then start another containiner running a node.js web service that needs to access this redis server:

$ docker run --link redis:db -d vagrant/nodejs

Docker will internally hook up these the two containers and pass host and port information to the node.js web service via environment variables:

DB_NAME=/romantic_lumiere/db
DB_PORT=tcp://172.17.0.5:6379
DB_PORT_6379_TCP=tcp://172.17.0.5:6379
DB_PORT_6379_TCP_ADDR=172.17.0.5
DB_PORT_6379_TCP_PORT=6379
DB_PORT_6379_TCP_PROTO=tcp

This library provides a helper parseLinks that will parse these environment variables into easily navigable Javascript objects.

Install

Install docker-links via npm

$ npm install docker-links

Example Usage

Consider a container that accesses three external services on two other containers. The first container exposes redis on port 6379 and postgres on 6500. The second container exposes redis on port 6379.

DB_NAME=/romantic_lumiere/db
DB_PORT=tcp://172.17.0.5:6379
DB_PORT_6379_TCP=tcp://172.17.0.5:6379
DB_PORT_6379_TCP_ADDR=172.17.0.5
DB_PORT_6379_TCP_PORT=6379
DB_PORT_6379_TCP_PROTO=tcp
DB_PORT_6500_TCP=tcp://172.17.0.5:6500
DB_PORT_6500_TCP_ADDR=172.17.0.5
DB_PORT_6500_TCP_PORT=6500
DB_PORT_6500_TCP_PROTO=tcp
DB_REDIS_NAME=/romantic_lumiere/db_redis
DB_REDIS_PORT=tcp://172.17.0.2:6379
DB_REDIS_PORT_6379_TCP=tcp://172.17.0.2:6379
DB_REDIS_PORT_6379_TCP_ADDR=172.17.0.2
DB_REDIS_PORT_6379_TCP_PORT=6379
DB_REDIS_PORT_6379_TCP_PROTO=tcp

Parse with docker-links:

var links = require('docker-links').parseLinks(process.env);

Links is then the following object:

{
  "db": {
    "port": 6379,
    "hostname": "172.17.0.5",
    "url": "tcp://172.17.0.5:6379",
    "proto": "tcp",
    "name": "romantic_lumiere/db",
    "tcp": {
      "6379": {
        "hostname": "172.17.0.5",
        "url": "tcp://172.17.0.5:6379"
      },
      "6500": {
        "hostname": "172.17.0.5",
        "url": "tcp://172.17.0.5:6500"
      }
    }
  },
  "db_redis": {
    "port": 6379,
    "hostname": "172.17.0.2",
    "url": "tcp://172.17.0.2:6379",
    "proto": "tcp",
    "name": "romantic_lumiere/db_redis",
    "tcp": {
      "6379": {
        "hostname": "172.17.0.2",
        "url": "tcp://172.17.0.2:6379"
      }
    }
  }
}