Unable to communicate with the postgreSQL database using Docker - postgresql

Question

I don't know why I am not able to fetch data from my postgreSQL database. I always got the same error when I do :
docker logs web I got that :
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
I tried a lot of things but without effects...
Here is my docker-compose :
version: '3.7'
services:
web:
container_name: web
build:
context: .
dockerfile: Dockerfile
command: python manage.py runserver 0.0.0.0:8000
volumes:
- .:/usr/src/web/
ports:
- 8000:8000
- 3000:3000
- 5432:5432
stdin_open: true
depends_on:
- db
db:
container_name: db
image: postgres:12.0-alpine
volumes:
- postgres_data:/var/lib/postgresql/data/
environment:
- POSTGRES_HOST_AUTH_METHOD=trust
- POSTGRES_USER=admin
- POSTGRES_PASSWORD=pass
- POSTGRES_DB=mydb
- POSTGRES_HOST=localhost
volumes:
postgres_data:
And this is the dockerfile :
# pull official base image
FROM python:3.8.3-alpine
# set work directory
WORKDIR /usr/src/web
# set environment variables
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1
# install psycopg2 dependencies
RUN apk update \
&& apk add postgresql-dev gcc python3-dev musl-dev
RUN apk add zlib-dev jpeg-dev gcc musl-dev
# install nodejs
RUN apk add --update nodejs nodejs-npm
# copy project
ADD . .
# install dependencies
RUN pip install --upgrade pip
RUN pip install -r requirements.txt
in my settings.py I have this for the database :
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.postgresql_psycopg2',
'NAME': 'mydb',
'USER': 'admin',
'PASSWORD': 'pass',
'HOST': 'localhost',
'PORT': '5432',
}
}
Could you help me please ?
I have absolutely no ideas how to solve that, I tried a lot of things but without any effects...
For instance, I tried to change in settings this parameter :
'HOST': 'localhost' to 'HOST':'db'
But I got that errors when I type that docker logs web :
django.db.utils.OperationalError: FATAL: password authentication failed for user "admin"
Thank you very much

Answer 1

have you tried to EXPOSE the port 5432 on the database container?
something like
db:
container_name: db
image: postgres:12.0-alpine
volumes:
- postgres_data:/var/lib/postgresql/data/
environment:
- POSTGRES_HOST_AUTH_METHOD=trust
- POSTGRES_USER=admin
- POSTGRES_PASSWORD=pass
- POSTGRES_DB=mydb
- POSTGRES_HOST=localhost
expose:
- "5432"
or inside the Dockerfile EXPOSE 5432/tcp
here is a link where you can check out the difference between ports: and expose:
What is the difference between docker-compose ports vs expose