docker-compose to run django with mongodb

Question

I am facing problem using docker-compose to link a django container with postgres and mongo containers? I am trying to use "docker-compose up" which starts up the mongo and postgres containers (as I need to link both) but still the django app is not able to connect to mongodb on default settings. My django-compose.yml file contents are copied below:

    db1:
      image: postgres
    db2:
      image: mongo
      ports:
        - "27017:27017"
    web:
      build: .
      command: python manage.py runserver 0.0.0.0:8000
      volumes:
        - .:/code
      ports:
        - "8000:8000"
      links:
        - db1
        - db2

It does connect with postgres with default settings. I can also telnet to the mongodb port locally. Still, I get this error on starting the web container:

File "/usr/local/lib/python2.7/site-packages/mongoengine/connection.py", line 124, in get_connection web_1 | raise ConnectionError("Cannot connect to database %s :\n%s" % (alias, e)) web_1 | mongoengine.connection.ConnectionError: Cannot connect to database default : web_1 | [Errno 111] Connection refused

PS: I had successfully started a django-postgres connected app on my localhost, but it failed connecting to db, on an AWS instance. That is another problem I still need to get to root of.

Answer 1

I ran into a similar problem but with another service (not MongoDB). I'm not sure of what I'm doing wrong but this is how I could solve it :

import os
import mongoengine

MONGODB_HOST = os.environ.get('DB2_PORT_27017_TCP_ADDR', '127.0.0.1')
mongoengine.connect(host=MONGODB_HOST)

• With DB2 being the name of your service in docker-compose.yml
• 27017 being the port of the exposed service.
• More about docker-compose environment variables
• I'd put that in my settings file. But you are free to put it wherever you think it's appropriate depending on your project architecture

UPDATE

Now docker-compose containers are reachable by other services using a hostname similar to their alias. link documentation :

Containers for the linked service will be reachable at a hostname identical to the alias, or the service name if no alias was specified.

And that way you can connect to MongoDB like this:

import mongoengine

mongoengine.connect(host="db2")

Answer 2

You should specify host name like in the docker compose file, instead of IP address.

I've faced similar problems in connecting from a Tornado Web app to Mongo DB. Here is my docker-compose.yml:

web:
  build: .
  ports:
   - "8888:8888"
  volumes:
   - .:/code
  links:
   - db
db:
  image: mongo:3.0

Here is my connection string:

motorengine.connect("db", host='db', port=27017, io_loop=io_loop)

My error was to specify IP address instead of host name (db) like in the docker compose file.