Docker/ Django/ Postgres - could not translate host name "db" to address: Name or service not known

Question

Few days ago I asked a question about a Postgres error.

I followed your suggestions and they helped a bit but in addition to not solving my problem some new problems arose.

I have a django-postgres app which works locally with no problems. When I try to build a docker image it builds but when I try to set up the container I have the following error:

django.db.utils.OperationalError: could not translate host name "db" to address: Name or service not known

I'll show you my Dockerfile:

# Origin image
FROM python:3.8

RUN apt-get update

# Define directory
RUN mkdir /project
WORKDIR /project

# Install requirements
RUN apt-get install -y vim
RUN python -m pip install --upgrade pip
COPY requirements.txt /project/
RUN pip install -r requirements.txt
COPY . /project/

# Expose some ports
EXPOSE 22 5432 8080 8009 8000

# default command
CMD ["python", "manage.py", "runserver", "0.0.0.0:8000"]

And here is my docker-compose file:

version: "3.3"

services:
  db:
    image: postgres
    volumes:
      - ./data/db:/var/lib/postgresql/data
    ports:
      - "5432:5432"
    environment:
      - POSTGRES_NAME=plataforma
      - POSTGRES_USER=admin
      - POSTGRES_PASSWORD=administrador
  web:
    build: .
    command: python manage.py runserver 0.0.0.0:8000
    volumes:
      - .:/code
    ports:
      - "8000:8000"
    environment:
      - POSTGRES_NAME=plataforma
      - POSTGRES_USER=admin
      - POSTGRES_PASSWORD=administrador
    depends_on:
      - db
    env_file:
      - ./plataforma/.env

On settings.py I configure the database on this way:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': env('POSTGRESQL_NAME'),
        'USER': env('POSTGRESQL_USER'),
        'PASSWORD': env('POSTGRESQL_PASS'),
        'HOST': env('POSTGRESQL_HOST'),
        'PORT': env('POSTGRESQL_PORT'),
    }
}

And this is my .env file:

POSTGRESQL_NAME=plataforma
POSTGRESQL_USER=admin
POSTGRESQL_PASS=administrador
POSTGRESQL_HOST=db
POSTGRESQL_PORT=5432

When I run my app locally I use localhost instead db for POSTGRESQL_HOST. Now, when I run $ sudo docker-compose run web python manage.py runserver . the image builds and the database container is running, but the app container is stopped. If I run $ docker start container-name it doesn't start.

If I run $ docker run -d --restart always --name new-container-name image-name a new container starts correctly and if I get inside it and try to make django migrations, i have the same error:

/usr/local/lib/python3.8/site-packages/django/core/management/commands/makemigrations.py:105: RuntimeWarning: Got an error checking a consistent migration history performed for database connection 'default': could not translate host name "db" to address: Name or service not known

Maybe I am using the docker-compose file in a wrong way. I've tried to install postgres from Dockerfile direct but there I have the error from my last question:

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?

Also I tried this solution and this solution but they didn't work either.

So, I am literally lost. I also have read this docker Quickstart but I don't figure out of what I'm doing wrong.

Can anyone help me?

Sorry if I'm misunderstanding some stackoverflow rules, but I'm still figuring out how it works.

Thankyou!

EDIT: Thanks to @DavidMaze 's help we found out what the problem was! David said:

The postgres image accepts an environment variable POSTGRES_DB to set the initial database name, not POSTGRES_NAME; does changing this (and deleting the ./data/db host directory) help?

So I Changed POSTGRES_NAME variable to POSTGRES_DB and erased /data folder (and purged images and containers list) and ran docker-compose up At the beginning when I run that command for the first time it seems like it try to setup first the web container and fails (with OperationalError), but when I run the same command again it works without errors.

Thank you so much for the help!