Docker-compose external_links not able to connect
<p>I have a couple of app containers that I want to connect to the mongodb container. I tried with external_links but I can not connect to the mongodb.</p>

<p>I get</p>

<blockquote>
  <p>MongoError: failed to connect to server [mongodb:27017] on first
  connect</p>
</blockquote>

<p>Do I have to add the containers into the same network to get external_links working?</p>

<p><strong>MongoDB:</strong></p>

<pre><code>version: '2'
services:
  mongodb:
    image: mongo:3.4
    restart: always
    ports:
      - "27017:27017"
    volumes:
      - data:/data/db
volumes:
  data:
</code></pre>

<p><strong>App:</strong></p>

<pre><code>version: '2'
services:
  app-dev:
    restart: Always
    build: repository/
    ports:
      - "3000:80"
    env_file:
      - ./environment.env
    external_links:
      - mongodb_mongodb_1:mongodb
</code></pre>

<p><strong>Networks:</strong></p>

<pre><code># sudo docker network ls
NETWORK ID          NAME                      DRIVER              SCOPE
29f8bae3e136        bridge                    bridge              local
67d5519cb2e6        dev_default               bridge              local
9e7097c844cf        host                      host                local
481ee4301f7c        mongodb_default           bridge              local
4275508449f6        none                      null                local
873a46298cd9        prod_default              bridge              local
</code></pre>