Postgres to Ubuntu Docker container linking not working - django

Question

[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?

Answer 1

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=#