Postgres to Ubuntu Docker container linking not wo

[EDIT]: I'm able to reproduce this without any of my own custom code. I just created a fresh Linode image running Ubuntu 14.04 and installed Docker according to the steps on Docker's website.

I then ran:

docker run -d --name db postgres

and can see it running:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS               NAMES
9d335e8fc70b        postgres            "/docker-entrypoint.   7 minutes ago       Up 7 minutes        5432/tcp            db

Then I start an interactive Ubuntu container, linked to db, and try to test the link via nc and curl:

$docker run -it --link db ubuntu /bin/bash
root@eb02f4e7b89e:/# apt-get install curl
...
root@eb02f4e7b89e:/# curl http://$DB_PORT_5432_TCP_ADDR:$DB_PORT_5432_TCP_PORT/
curl: (7) Failed to connect to 172.17.0.2 port 5432: Connection timed out

What am I missing?

I'm trying to link a postgres container with an app container running Django but it doesn't seem to be linking properly.

The commands to start the containers were:

$ docker run -d --name db postgres
$ docker run -d --name web --link db -p 8000:80 test_image

Both containers appear to be running fine:

$ docker ps
CONTAINER ID        IMAGE                           COMMAND                CREATED             STATUS              PORTS                  NAMES
5838047eb14c        test_image                      "/test/.docker/st      40 minutes ago      Up 40 minutes       0.0.0.0:8000->80/tcp   web                 
d2d6754430a2        postgres                        "/docker-entrypoint.   44 minutes ago      Up 44 minutes       5432/tcp               db

And seem to be correctly linked:

$ docker inspect -f "{{ .HostConfig.Links }}" web
[/db:/web/db]

However, when I try to run "python manage.py migrate" in the web container it doesn't seem to be able to connect to the postgres container:

# python manage.py migrate
Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 390, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 441, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/migrate.py", line 93, in handle
    executor = MigrationExecutor(connection, self.migration_progress_callback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 19, in __init__
    self.loader = MigrationLoader(self.connection)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/loader.py", line 47, in __init__
    self.build_graph()
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/loader.py", line 180, in build_graph
    self.applied_migrations = recorder.applied_migrations()
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/recorder.py", line 59, in applied_migrations
    self.ensure_schema()
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/recorder.py", line 49, in ensure_schema
    if self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor()):
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 164, in cursor
    cursor = self.make_cursor(self._cursor())
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 135, in _cursor
    self.ensure_connection()
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 130, in ensure_connection
    self.connect()
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 97, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 130, in ensure_connection
    self.connect()
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 119, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 172, in get_new_connection
    connection = Database.connect(**conn_params)
  File "/usr/lib/python2.7/dist-packages/psycopg2/__init__.py", line 179, in connect
    connection_factory=connection_factory, async=async)
django.db.utils.OperationalError: could not connect to server: Connection timed out
        Is the server running on host "db" (172.17.0.42) and accepting
        TCP/IP connections on port 5432?

I'm able to connect to the postgres container directly:

$ docker exec -it db bash
root@d2d6754430a2:/# cat /etc/hosts
172.17.0.42     d2d6754430a2
127.0.0.1       localhost
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
root@d2d6754430a2:/# su postgres
$ psql
psql (9.4.4)
Type "help" for help.

postgres=#

But not from inside the web container:

# curl http://$DB_PORT_5432_TCP_ADDR:$DB_PORT_5432_TCP_PORT/
curl: (7) Failed to connect to 172.17.0.42 port 5432: Connection timed out

My host machine is running Ubuntu 14.04.

Any ideas what I'm missing?

Check that your postgresql.conf has listen_addresses = '*'

The default is listen_addresses = 'localhost', which would behave in the manner you describe.

Edit:

This works for me, does it work for you?

$ docker pull postgres
$ docker pull django
$ docker run -d --name db -d postgres
$ docker run -it --link db:db django bash
root@11c767bd3d09:/#  psql -h db -U postgres
psql (9.4.3, server 9.4.4)
Type "help" for help.

postgres=#

Edit (Docker 1.7.1 output)

$ docker rm $(docker ps -a -q)
$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
django              latest              29755dd6751b        3 days ago          434.5 MB
postgres            latest              f33438ff9aef        3 days ago          265.5 MB
$ docker -v
Docker version 1.7.1, build 786b29d
$ docker run -d --name db -d postgres
$ docker run -it --link db:db django bash
root@11c767bd3d09:/#  psql -h db -U postgres
psql (9.4.3, server 9.4.4)
Type "help" for help.

postgres=#