Django can't connect to Postgres in Docker setup

Question

I'm setting up an application in Docker that uses Django and Postgres. I'm unable to connect to Postgres from the app. When I run either:

docker-compose run web python manage.py runserver
docker-compose run web python manage.py migrate

I get the following error:

django.db.utils.OperationalError: could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

Here's my Dockerfile:

FROM python:2.7

ADD requirements.txt /app/requirements.txt

WORKDIR /app/

RUN pip install -r requirements.txt

My docker-compose.yml:

version: '2'
services:
  db:
    image: postgres:9.4
    hostname: db
    environment:
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=postgres
      - POSTGRES_DB=postgres
    ports:
      - "5432:5432"

  web:
    build:
      context: .
      dockerfile: Dockerfile
    hostname: web
    volumes:
      - .:/app
    ports:
      - "8000:8000"
    links:
      - db
    depends_on:
      - db
    command:
      python manage.py runserver 0.0.0.0:8000

and the database settings in Django:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'postgres',
        'USER': 'postgres',
        'HOST': 'db',
        'PORT': 5432,
    }
}

docker ps -a shows:

e9df7e1644ce        web             "python manage.py ..."   About a minute ago   Up About a minute          0.0.0.0:8000->8000/tcp   web_1
60801d3256e4        postgres:9.4        "docker-entrypoint..."   About a minute ago   Up About a minute          0.0.0.0:5432->5432/tcp   db_1

Django v1.10.5
Docker for Mac v1.13.1
docker-compose v 1.11.1

Here are the logs:

Check your Docker logs, it's possible that the web container is being spun up before the db container and hence the dependency doesn't resolve. — Anomitra
– Anomitra, Commented Feb 17, 2017 at 20:47
I thought depends_on: - db would prevent the web container from being spun up before the db container, no? — Steven Mercatante
– Steven Mercatante, Commented Feb 17, 2017 at 20:50
Oddly enough, there's nothing in the docker logs for the web container. It says in the very beginning Attached to web_1, db_1, and then it's just a bunch of logs from db_1. — Steven Mercatante
– Steven Mercatante, Commented Feb 17, 2017 at 20:51
You're absolutely correct, but I ran into this problem a couple of days ago - I was using links however. Worth checking it out anyway. Can you attach the logs to the question so that anyone looking at it can understand the situation better? — Anomitra
– Anomitra, Commented Feb 17, 2017 at 20:52
Somehow you have to tell your app to connect to postgress over TCP/IP instead of locally via sockets. Not sure with django though. — user2105103
– user2105103, Commented Feb 17, 2017 at 21:05

Steven Mercatante · Accepted Answer · 2017-02-19 01:03:54Z

Turns out the issue was that Postgres hadn't fully spun up before starting the Django app. This was easily solved by waiting a few seconds before starting the web server. I set the command for my web service to ./bin/boot.sh, and the contents of that file are:

#!/bin/sh

# wait for Postgres to start
sleep 10

python manage.py migrate

python manage.py runserver 0.0.0.0:8000

Edit

This method might not be good enough depending on your application - sleeping for 10 seconds works for me, most of the time, but it's possible that postgres will take 11 seconds to spin up. Here's an improved bash file, with a function I took from this example.

#!/bin/bash

# wait for Postgres to start
function postgres_ready(){
python << END
import sys
import psycopg2
try:
    conn = psycopg2.connect(dbname="postgres", user="postgres", password="postgres", host="postgres")
except psycopg2.OperationalError:
    sys.exit(-1)
sys.exit(0)
END
}

until postgres_ready; do
  >&2 echo "Postgres is unavailable - sleeping"
  sleep 1
done

python manage.py migrate

gunicorn pft.wsgi:application -w 2 -b 0.0.0.0:8000 --reload

A small modification, after doing conn = "", make conn.close ()
This saved me! Thank you. Seems like this kind of sleep 10 situation should be handled a little better behind the scenes though...

Soorena · Accepted Answer · 2018-07-14 11:11:59Z

0

I had this problem and it was only because I was using a VPN. If you are using something like sshuttle just turn it off.

answered Jul 14, 2018 at 11:11

Soorena

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