How to connect a Docker container to PostgreSQL running on the localhost using a DATABASE_URL?

Question

I'm following the Aptible Django Quickstart Tutorial which described how to create and deploy an app Aptible's PaaS. I would also like to be able to run the Docker container with the Django app locally and connect to a local PostgreSQL database, however, and it is unclear to me how to do this.

The Dockerfile for the Django app is:

FROM python:3.6

# System prerequisites
RUN apt-get update \
 && apt-get -y install build-essential libpq-dev \
 && rm -rf /var/lib/apt/lists/*

# If you require additional OS dependencies, install them here:
# RUN apt-get update \
#  && apt-get -y install imagemagick nodejs \
#  && rm -rf /var/lib/apt/lists/*

# Install Gunicorn. If Gunicorn is already present in your requirements.txt,
# you don't need that (but if won't hurt).
RUN pip install gunicorn

ADD requirements.txt /app/
WORKDIR /app
RUN pip install -r requirements.txt

ADD . /app

EXPOSE 8000

CMD ["gunicorn", "--access-logfile=-", "--error-logfile=-", "--bind=0.0.0.0:8000", "--workers=3", "mysite.wsgi"]

where mysite is the name of the Django app. Its settings.py uses dj-database-url as follows:

import dj_database_url
DATABASES = {'default': dj_database_url.config()}

In order to connect to a local instance of PostgreSQL, it would seem I should follow the Docker for Mac Solution on Allow docker container to connect to a local/host postgres database:

docker run -e DB_PORT=5432 -e DB_HOST=docker.for.mac.host.internal

However, if I try this I still get an error ending with

  File "/usr/local/lib/python3.6/site-packages/psycopg2/__init__.py", line 130, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
django.db.utils.OperationalError: 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?
could not connect to server: Cannot assign requested address
    Is the server running on host "localhost" (::1) and accepting
    TCP/IP connections on port 5432?

It would seem to me that the app as currently configured is not 'doing anything' with the DB_PORT and DB_HOST environment variables, because it is reading these in one go from the DATABASE_URL. Is this the problem? If so, how could I fix this while still using DATABASE_URL as this appears to be the 'interface' to Aptible?

if you are using multiple containers it is better to use docker-compose.yml, docker has even docs for postgres and django docs.docker.com/compose/django/#create-a-django-project — Mazel Tov
– Mazel Tov, Commented Feb 5, 2018 at 20:39
Unfortunately, it's not possible to use Docker Compose on the Aptible platform; they have their own Services and Databases. — Kurt Peek
– Kurt Peek, Commented Feb 7, 2018 at 23:17

Kurt Peek · Accepted Answer · 2018-02-05 21:43:25Z

4

I managed to fix the problem by changing the DATABASE_URL in the .env file from

DATABASE_URL=postgres://my_app:my_password@localhost/my_database

to

DATABASE_URL=postgres://my_app:[email protected]/my_database

and running the container, which I tagged lucy_web, like so:

docker run -p 8000:8000 --env-file .env lucy_web

It was not necessary to change listen_addresses to '*' in my postgresql.conf; this was still at its default, localhost. (I believe this is because the -p 8000:8000 argument maps port 8000 on localhost to the container).

answered Feb 5, 2018 at 21:43

Kurt Peek

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Comments

Darwin · Accepted Answer · 2018-02-05 21:04:25Z

As I understand, postgres is not running on a container but as a service on your host os, right?

Please theck below:

1. Check your postgres accepts connections on all ip addresses

Usually postgres listens to localhost only, that means, connections to other than localhost are refused. Each docker container is attached to a virtual network and communication from container to host happens through that virtual network.

Update your postgresql.conf file and add:

listen_addresses = '*'          # what IP address(es) to listen on;
                                    # comma-separated list of addresses;
                                    # defaults to 'localhost'; use '*' for all
                                    # (change requires restart)

2. Use correct ip address/hostname

As stated before, container communicates to host through this virtual network. Make sure your are using the correct hostname or ip address.

localhost

localhost is not going to work because from within the container context, localhost refers to the container

docker.for.mac.host.internal

At least for me it doesn't work (docker-ce on a mac), see that host resolution is not working

docker run --rm -it postgres:10 ping docker.for.mac.host.internal
ping: unknown host

use your ip address

I'm using my the ip address given by my dhcp server, ping works

docker run --rm -it postgres:10 ping 192.168.0.* -c 1
PING 192.168.0.* (192.168.0.*): 56 data bytes
64 bytes from 192.168.0.*: icmp_seq=0 ttl=37 time=0.455 ms

So try using a valid ip address, either the ip of the docker device or the ip from your physical network interface.

3. Use a docker compose file

Use a docker compose file to run with either compose or swarm, see sample application here: https://docs.docker.com/engine/swarm/stack-deploy/#create-the-example-application

Iyanu Akin's · Accepted Answer · 2021-02-14 18:43:10Z

0

Windows user configure their env to use:

DATABASE_URL=postgres://my_app:[email protected]/my_database

answered Feb 14, 2021 at 18:43

Iyanu Akin's

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How to connect a Docker container to PostgreSQL running on the localhost using a DATABASE_URL?

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1. Check your postgres accepts connections on all ip addresses

2. Use correct ip address/hostname

3. Use a docker compose file

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1. Check your postgres accepts connections on all ip addresses

2. Use correct ip address/hostname

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