Linking Django and Postgresql with Docker

Question

I have two Docker containers. The first one is Postgresql container, which I run using the following command.

sudo docker run -v /home/mpmsp/project/ezdict/postgresql/data:/var/lib/postgresql/data -p 127.0.0.1:5432:5432  -name my-postgres -d postgres

It is based on official image and it is working perfectly, I can connect to Postgresql from the host.

The second container is a container with my Django application. The image is built using the following Dockerfile (based on this image):

FROM python:3-onbuild
EXPOSE 8000 5432
CMD ["/bin/bash"]

And I run this container with the following command

sudo docker run --link my-postgres:my-postgres -v /home/mpmsp/project/ezdict/ezbkend:/usr/src/app -name my-app -i -t my-app

docker ps output shows that containers are linked

NAMES
my-app/my-postgres, my-postgres

However, when I go to localhost:8000, I see an error page from Django, with the following output

OperationalError at /api-auth/login/
could not connect to server: Connection refused
    Is the server running on host "127.0.0.1" and accepting
    TCP/IP connections on port 5432?
Request Method: GET
Request URL:    http://127.0.0.1:8000/api-auth/login/
Django Version: 1.6.4
Exception Type: OperationalError
Exception Value:    
could not connect to server: Connection refused
    Is the server running on host "127.0.0.1" and accepting
    TCP/IP connections on port 5432?
Exception Location: /usr/local/lib/python3.4/site-packages/psycopg2/__init__.py in     connect, line 164
Python Executable:  /usr/local/bin/python
Python Version: 3.4.1
Python Path:    
['/usr/src/app',
 '/usr/local/lib/python34.zip',
 '/usr/local/lib/python3.4',
 '/usr/local/lib/python3.4/plat-linux',
 '/usr/local/lib/python3.4/lib-dynload',
 '/root/.local/lib/python3.4/site-packages',
 '/usr/local/lib/python3.4/site-packages']
Server time:    Птн, 10 Окт 2014 12:07:07 +0400

Application's settings.py

  DATABASES = {
   'default': {
       'ENGINE': 'django.db.backends.postgresql_psycopg2',
       'NAME': 'mydb',                      
       'USER': 'postgres',
       'PASSWORD': '',
       'HOST': '127.0.0.1',                      
       'PORT': '5432',                      
    }
  }

How to make linking work? Thanks in advance

Answer 1

The Dockerfile for your Django image should not expose port 5432 as no Postgresql server will be running in any container created from that image:

FROM python:3-onbuild
EXPOSE 8000
CMD ["/bin/bash"]

Then as you are running the Django container linking it with

--link my-postgres:my-postgres

your settings for the database are incorrect.

In the Django container: 127.0.0.1 refers to the Django container which isn't running any service listening on port 5432.

So your settings.py file should be:

  DATABASES = {
   'default': {
       'ENGINE': 'django.db.backends.postgresql_psycopg2',
       'NAME': 'mydb',                      
       'USER': 'postgres',
       'PASSWORD': '',
       'HOST': 'my-postgres',                      
       'PORT': '5432',                      
    }
  }

As you run your Django container with:

sudo docker run --link my-postgres:db -v /home/mpmsp/project/ezdict/ezbkend:/usr/src/app -name my-app -i -t my-app

then your settings.py file would have to be:

  DATABASES = {
   'default': {
       'ENGINE': 'django.db.backends.postgresql_psycopg2',
       'NAME': 'mydb',                      
       'USER': 'postgres',
       'PASSWORD': '',
       'HOST': 'db',                      
       'PORT': '5432',                      
    }
  }