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

Question

I am new to Docker and Postgres and was following book 'Django for professionals' from William S. Vincent to learn this. I was trying to connect to PostgreSQL with Docker containers.

What I did:

1> Written Docker file:

# Pull base image
FROM python:3.7
# Set environment variables
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1
# Set work directory
WORKDIR /code
# Install dependencies
COPY Pipfile Pipfile.lock /code/
RUN pip install pipenv && pipenv install --system
# Copy project
COPY . /code/

2> Written docker-compose.yml file:

version: "3.7"

services:
  web:
    build: .
    command: python /code/manage.py runserver 0.0.0.0:8000
    volumes:
      - .:/code
    ports:
      - 8000:8000
    depends_on:
      - db
  db:
    image: postgres:11

3> Changed settings.py:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'postgres',
        'USER': 'postgres',
        'PASSWORD': 'postgres',
        'HOST': 'db',docker-compose up -d --build
        'PORT': 5432
    }
}

4> installed psycopg2

docker-compose exec web pipenv install psycopg2-binary==2.8.3

5> Run docker-compose to rebuild the image:

docker-compose up -d --build

Which throws an error when I check the docker-compose logs as:

Attaching to postgresql_web_1, postgresql_db_1
web_1  | Watching for file changes with StatReloader
web_1  | Performing system checks...
web_1  |
web_1  | System check identified no issues (0 silenced).
web_1  | Exception in thread django-main-thread:
web_1  | Traceback (most recent call last):
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 217, in ensure_connection
web_1  |     self.connect()
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 195, in connect
web_1  |     self.connection = self.get_new_connection(conn_params)
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/postgresql/base.py", line 178, in get_new_connection
web_1  |     connection = Database.connect(**conn_params)
web_1  |   File "/usr/local/lib/python3.7/site-packages/psycopg2/__init__.py", line 126, in connect
web_1  |     conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
web_1  | psycopg2.OperationalError: could not translate host name "db" to address: Name or service not known
web_1  |
web_1  |
web_1  | The above exception was the direct cause of the following exception:
web_1  | 
web_1  | Traceback (most recent call last):
web_1  |   File "/usr/local/lib/python3.7/threading.py", line 926, in _bootstrap_inner
web_1  |     self.run()
web_1  |   File "/usr/local/lib/python3.7/threading.py", line 870, in run
web_1  |     self._target(*self._args, **self._kwargs)
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/utils/autoreload.py", line 54, in wrapper
web_1  |     fn(*args, **kwargs)
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/core/management/commands/runserver.py", line 120, in inner_run
web_1  |     self.check_migrations()
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 453, in check_migrations
web_1  |     executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/migrations/executor.py", line 18, in __init__
web_1  |     self.loader = MigrationLoader(self.connection)
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/migrations/loader.py", line 49, in __init__
web_1  |     self.build_graph()
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/migrations/loader.py", line 212, in build_graph
web_1  |     self.applied_migrations = recorder.applied_migrations()
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/migrations/recorder.py", line 73, in applied_migrations
web_1  |     if self.has_table():
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/migrations/recorder.py", line 56, in has_table
web_1  |     return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 256, in cursor
web_1  |     return self._cursor()
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 233, in _cursor
web_1  |     self.ensure_connection()
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 217, in ensure_connection
web_1  |     self.connect()
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/utils.py", line 89, in __exit__
web_1  |     raise dj_exc_value.with_traceback(traceback) from exc_value
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 217, in ensure_connection
web_1  |     self.connect()
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 195, in connect
web_1  |     self.connection = self.get_new_connection(conn_params)
web_1  |   File "/usr/local/lib/python3.7/site-packages/django/db/backends/postgresql/base.py", line 178, in get_new_connection
web_1  |     connection = Database.connect(**conn_params)
web_1  |   File "/usr/local/lib/python3.7/site-packages/psycopg2/__init__.py", line 126, in connect
web_1  |     conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
web_1  | django.db.utils.OperationalError: could not translate host name "db" to address: Name or service not known
db_1   | Error: Database is uninitialized and superuser password is not specified.
db_1   |        You must specify POSTGRES_PASSWORD to a non-empty value for the
db_1   |        superuser. For example, "-e POSTGRES_PASSWORD=password" on "docker run".
db_1   |
db_1   |        You may also use "POSTGRES_HOST_AUTH_METHOD=trust" to allow all
db_1   |        connections without a password. This is *not* recommended.
db_1   |
db_1   |        See PostgreSQL documentation about "trust":
db_1   |        https://www.postgresql.org/docs/current/auth-trust.html
web_1  |
web_1  |

I have tried various answers on similar issues on Stack Overflow but nothing seems to work for me. I have tried added :

environment:
    - "POSTGRES_HOST_AUTH_METHOD=trust"

to db as in this

and also various other answers.

Could be possible that the postgres container is not yet up-running, and before that you are making call to DB. To understand more on this [Controlling startup order ](docs.docker.com/compose/startup-order) — Saurabh
– Saurabh, Commented Jun 13, 2020 at 18:10

Amir2170 · Accepted Answer · 2020-11-08 22:58:46Z

0

i'm following the same toturial as you and i had the same problem it works when you add:

environment:
  POSTGRES_USER: postgres
  POSTGRES_PASSWORD: postgres

to the end of db service

answered Nov 8, 2020 at 22:58

Amir2170

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