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I have the following containers running:

$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES b02d801f9aa3 development_mongo "docker-entrypoint.s…" 7 hours ago Up About an hour 0.0.0.0:50001->27017/tcp compose_mongo 2903bb830ea7 development_postgres "docker-entrypoint.s…" 7 hours ago Up About an hour 0.0.0.0:50000->5432/tcp compose_postgres 6ce3fe015a8f development_elastic "/usr/local/bin/dock…" 7 hours ago Up About an hour 0.0.0.0:50002->9200/tcp, 0.0.0.0:50003->9300/tcp compose_elastic

When I create/run a Docker container that has python manage.py makemigrations as entrypoint, the Django app can't connect to the Postgres container:

 $ docker run --name test1 repo/myapp:stage_1605191501 Traceback (most recent call last): File "/usr/local/lib/python3.6/dist-packages/django/db/backends/base/base.py", line 217, in ensure_connection self.connect() File "/usr/local/lib/python3.6/dist-packages/django/db/backends/base/base.py", line 195, in connect self.connection = self.get_new_connection(conn_params) File "/usr/local/lib/python3.6/dist-packages/django/db/backends/postgresql/base.py", line 178, in get_new_connection connection = Database.connect(**conn_params) File "/usr/local/lib/python3.6/dist-packages/psycopg2/__init__.py", line 126, in connect conn = _connect(dsn, connection_factory=connection_factory, **kwasync) psycopg2.OperationalError: could not connect to server: Connection refused Is the server running on host "0.0.0.0" and accepting TCP/IP connections on port 50000?

Why it cannot connect, since that Postgres port is already exposed to the host? What am I missing?

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  • Please show your docker-compose.yml file. Commented May 17, 2019 at 4:40
  • I already got the problem, Michael: different networks. Some containers using a custom network and other container connected only to default bridge. I posted the answer below. Thanks :)! Commented May 17, 2019 at 4:42

1 Answer 1

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Basically, all compose_* containers, are attached to a different Docker Network, as well as test1, is associated to another network.

$ docker network inspect development_default | grep 'Name\|IPv4' "Name": "development_default", "Name": "compose_postgres", "IPv4Address": "172.20.0.2/16", "Name": "compose_elastic", "IPv4Address": "172.20.0.4/16", "Name": "compose_mongo", "IPv4Address": "172.20.0.3/16",

These containers were created through Docker Compose, without specifying a custom network. If no custom network is defined on your Docker Compose file, docker will create a custom network which uses the name of the directory from were you have your build environment. That's why the development, name of the directory which was holding the files for generating these containers, was used when creating a development_default network for them.

  • When executed the command $ docker run --name test1 repo/myapp:stage_1605191501, no --network was specified, so test1 will be associated to the default bridge network.

  • compose_postgres has 5432 port exposed to the host network and it is associated to development_default network (172.20.0.0/16).

Answer (steps):

  1. provide static IP for compose_postgres
  2. define this IP for the Django app definitions, inside the image of test1, in order to provide connection from the app to compose_postgres database
  3. define development_default as the --network for test1 when running docker run

For further reference:

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  • You don't need the compose_ part, that's the project name in compose which can change. Set it to postgres, elastic, and mongo for the hostnames instead. You'll see network aliases configured for these when deploying your project in compose. Commented May 17, 2019 at 12:33

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