Docker-compose: App container can't connect to Postgres

Question

Using docker-compose, I'm trying to view a Flask app from manage.py runserver that connects with a postgres image but I get the following error:

sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) could not connect to server: Connection refused
    Is the server running on host "0.0.0.0" and accepting
    TCP/IP connections on port 5432?

MY COMPOSE FILE

version: '3.1'
services:
  app:
    build: .
    ports:
      - 5000:5000
    volumes:
      - /Users/sammy/Projects/my_flask_app:/my_flask_app
    container_name: my_flask_app_1
    depends_on:
      - db
    entrypoint: ["python", "manage.py", "runserver"]
  db:
    image: postgres:10
    restart: always
    container_name: my_app_db_1
    environment:
      POSTGRES_USER: ubuntu
      POSTGRES_PASSWORD: pickles
      POSTGRES_DB: db
    ports:
      - 5432:5432

FROM MY APP'S settings.py FILE

POSTGRES = {
    'user': "ubuntu",
    'pw': "pickles",
    'db': "db",
    'host': os.getenv('IP', '0.0.0.0'),
    'port': '5432',
}
SQLALCHEMY_DATABASE_URI = 'postgresql://%(user)s:\
%(pw)s@%(host)s:%(port)s/%(db)s' % POSTGRES

It builds and runs the app well as I can visit the site and see the Werkzeug traceback interpreter. I'm failing either on the configuration of the Postgres container itself or my Flask's connection to it.

Are the environmental variables correct?
Do I need to specify a volume for the DB? If so, why? I haven't understood the point of that other than tucking the username/pass into environmental variables.

You host should be "db"

Robert Moskal
– Robert Moskal

2018-05-31 15:10:29 +00:00
Commented May 31, 2018 at 15:10 — Robert Moskal
– Robert Moskal, Commented May 31, 2018 at 15:10

Robert Moskal · Accepted Answer · 2020-11-20 00:22:16Z

12

Your host in the settings.py file should be "db". compose exposes hosts on an internal network with the same host names as your services.

POSTGRES = {
    'user': "ubuntu",
    'pw': "pickles",
    'db': "db",
    'host': "db",
    'port': '5432',
}

edited Nov 20, 2020 at 0:22

answered May 31, 2018 at 15:11

Robert Moskal

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2 Comments

dadiletta Over a year ago

Are you suggesting I add a -host flag to my compose file? Do you know any any examples I could reference?

dadiletta Over a year ago

Thanks. I didn't realize the name of the service was the container's hostname. That's huge.

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