Connecting Django to Docker Postgres instance raising django.db.utils.OperationalError

Question

I'm trying to execute a django project on my local machine, the project requires Postgres.

I know close to nothing of docker. I pulled postgres image from docker hub and executed the followin command, as suggested by the instructions in postgres docker hub page.

$ docker run --name some-postgres -e POSTGRES_PASSWORD=mysecretpassword -d postgres

The docker container is up:

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
402180487f68        postgres            "docker-entrypoint.s…"   2 hours ago         Up 2 hours          5432/tcp            some-postgres

But I can't make Django to connect to it. (Django is running on my local machine, not on docker) Django settings:

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

If I execute migrations with the settings above the error is:

django.db.utils.OperationalError: could not connect to server: Connection refused
    Is the server running on host "localhost" (::1) and accepting
    TCP/IP connections on port 5432?
could not connect to server: Connection refused
    Is the server running on host "localhost" (127.0.0.1) and accepting
    TCP/IP connections on port 5432?

I assume the connection is not beign refused, because if I stop the container the error is the same.

Some tutorial/answer suggested HOST should be the container name. To me it doesn't make much sense, as I don't know how Django is supposed to resolve that, but I tried nonetheless:

        'HOST': 'some-postgres',

The error raised is:

django.db.utils.OperationalError: could not translate host name "some-postgres" to address: nodename nor servname provided, or not known

I have checked several questions and tutorials, but they all seem to use docker-composer and/or have the django project also inside docker. Still haven't been able to make the project connect to postgres.

I recommend docker-compose this will make your life much easier. This project of mine has a docker-compese.yml connecting django and postgres. github.com/DiegoMagg/caddy-django — Diego Magalhães
– Diego Magalhães, Commented Aug 12, 2020 at 20:42
I've avoided having to learn another thing on top of something I already know nothing, however if I were to use docker-compose, does that mean that both the django proj and postgres must run on a container? Or I can still have the django on local machine? (By local machine I mean not on a container) — Justcurious
– Justcurious, Commented Aug 12, 2020 at 20:52

Marek Piotrowski · Accepted Answer · 2020-08-12 20:55:37Z

1

I believe you have to forward port 5432 from the docker: https://docs.docker.com/config/containers/container-networking/#published-ports

Good analogy is a webserver - imagine you would start a django application in a container on port 8000. You couldn't just simply open firefox and navigate to localhost:8000 from within the host as the application is running in an isolated environment.

answered Aug 12, 2020 at 20:55

Marek Piotrowski

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1 Comment

Justcurious Over a year ago

Awesome! Couldn't find a way to do it with an already created instance, but $ docker run --name some-postgres -p 5432:5432 -e POSTGRES_PASSWORD=mysecretpassword -d postgres worked like a charm!

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