Docker compose port mapping
<p>I have a docker-compose yml file as in below</p>

<pre class="lang-yml prettyprint-override"><code>version: '2'
services:
  nodejs:
    build:
      context: .
      dockerfile: DockerFile
    ports:
      - "4000:4000"
    links:
      - redis
    expose:
      - "6379"
  redis:
    build:
      context: .
      dockerfile: Dockerfile-redis
</code></pre>

<p>My goal is to forward nodejs-127.0.0.1 port 6379 to the redis host.  I can already ping redis from the nodejs machine, but the ports are not mapped.  Tried expose options, but no chance either.</p>