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

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.