django.db.utils.OperationalError: could not connect to server: Connection refused

Question

I have 3 docker containers web(django), nginx, db(postgresql)

When I run the following command

docker-compose -f docker-compose.prod.yml exec web python manage.py migrate --noinput

The exact error is:

  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: Address not available
        Is the server running on host "localhost" (::1) and accepting
        TCP/IP connections on port 5432?

docker-compose.prod.yml

version: '3.7'

services:
  db:
    image: postgres:12.0-alpine
    volumes:
      - postgres_data:/var/lib/postgresql/data/
    env_file:
      - ./.envs/.db
  web:
    build:
      context: ./tubscout
      dockerfile: Dockerfile.prod
    command: gunicorn hello_django.wsgi:application --bind 0.0.0.0:8000
    volumes:
      - .static_volume:/home/app/web/staticfiles
    expose:
      - 8000
    env_file:
      - ./.envs/.prod
    depends_on:
      - db
  nginx:
    build: ./nginx
    volumes:
      - .static_volume:/home/app/web/staticfiles
    ports:
      - 1337:80
    depends_on:
      - web

volumes:
  postgres_data:
  static_volume:

Dockerfile.prod

###########
# BUILDER #
###########

# pull official base image
FROM python:3.8.3-alpine as builder

# set work directory
WORKDIR /usr/src/app

# set environment variables
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1

# install psycopg2 dependencies
RUN apk update \
    && apk add postgresql-dev gcc python3-dev musl-dev 

# install dependencies
RUN pip install --upgrade pip
COPY ./requirements.txt .
RUN pip wheel --no-cache-dir --no-deps -w /usr/src/app/wheels -r requirements.txt

#########
# FINAL #
#########

# pull official base image
FROM python:3.8.3-alpine

# create directory for the app user
RUN mkdir -p /home/app

# create the app user
RUN addgroup -S app && adduser -S app -G app

# create the appropriate directories
ENV HOME=/home/app
ENV APP_HOME=/home/app/web
RUN mkdir $APP_HOME
RUN mkdir $APP_HOME/staticfiles
WORKDIR $APP_HOME

# install dependencies
RUN apk update && apk add libpq
COPY --from=builder /usr/src/app /wheels
COPY --from=builder /usr/src/app/requirements.txt .
RUN pip install --no-cache /wheels/wheels/*

# copy entrypoint.sh
COPY ./entrypoint.sh $APP_HOME

# copy project
COPY . $APP_HOME

# chown all the files to the app user
RUN chown -R app:app $APP_HOME

# change to the app user
USER app

# run entrypoint.prod.sh
ENTRYPOINT ["/home/app/web/entrypoint.sh"]

settings.py

DATABASES = {
    'default': {
        "ENGINE": os.environ.get("SQL_ENGINE", "django.db.backends.sqlite3"),
        "NAME": os.environ.get("SQL_DATABASE", os.path.join(BASE_DIR, "db.sqlite3")),
        "USER": os.environ.get("SQL_USER", "user"),
        "PASSWORD": os.environ.get("SQL_PASSWORD", "password"),
        "HOST": os.environ.get("SQL_HOST", "localhost"),
        "PORT": os.environ.get("SQL_PORT", "5432"),
    }
}

./.envs/.db

POSTGRES_USER=postgres
POSTGRES_PASSWORD=123456789
POSTGRES_DB=tubscoutdb_prod

./.envs/.prod

DEBUG=0
SECRET_KEY='#yinppohul88coi7*f+1^_*7@o9u@kf-sr*%v(bb7^k5)n_=-h'
DJANGO_ALLOWED_HOSTS=localhost 127.0.0.1 [::1]
SQL_ENGINE=django.db.backends.postgresql
SQL_DATABASE=tubscoutdb_prod
SQL_USER=postgres
SQL_PASSWORD=123456789
SQL_HOST=localhost
SQL_PORT=5432
DATABASE=postgres

Answer 1

Change SQL_HOST to db in your .envs/.prod file. This will let the Web container reach the DB container and perform the migration.

Docker compose containers can be accessed with their service name from other containers.