I have a postgres container, docker-compose.yml:
services:
db:
container_name: db
expose:
- "5432"
ports:
- 5432:5432
volumes:
- postgres_data:/var/lib/postgresql/data/
And a django project with settings.py:
DATABASES = {
'default': {
'HOST': os.environ.get('POSTGRES_HOST', '127.0.0.1')
# etc
}
}
.env
POSTGRES_HOST_DJANGO=db
When I run my django app locally with manage.py runserver 0.0.0.0:8000 it connects fine, using the default POSTGRES_HOST=127.0.0.1, because .env isn't loaded.
I also run my django app in a container sometimes:
docker-compose.yml:
web:
#restart: unless-stopped
build: .
env_file: .env
command: bash -c "cd /app/src/ && python manage.py runserver 0.0.0.0:8000
volumes:
- .:/app
ports:
- 8000:8000
links:
- db:db
However it uses the .env file and connects with POSTGRES_HOST=db
If I try to connect the locally run django app with POSTGRES_HOST=db it fails:
django.db.utils.OperationalError: could not translate host name "db" to address: Name or service not known
And if I try to run the django app in a container with POSTGRES_HOST=127.0.0.1, it fails in the same way.
How can I get them to use the same POSTGRES_HOST?
The problem seems to be in the network config. I don't see one.
The default behavior of docker-compose is that it creates a network for every compose file - by default the name is the folder name with '_default'.
Django App is in a different network and Postgres is in a different network
If your Django app and your Postgres containers are in different docker-compose files, using container names to resolve hosts will not work(by default, can be done with a custom network config) as they are in two different networks.
As you have done a port binding, you can directly access Postgres by giving host machine's private ip and port 5432 in the container, this way communication is happening through the host network.
If you find a need to make the containers talk to each other directly, make sure they are on the same docker network
I figured out how to do it. It wasn't getting them to use the same variable, it was to get them to read different variables based on how it was run. So:
from docker-compose.yml
web:
build: .
command: bash -c "cd /app/src/ && python manage.py runserver 0.0.0.0:8000
env_file: .env
environment:
POSTGRES_HOST: db # takes precendent over .env file
And in .env:
POSTGRES_HOST=127.0.0.1
Now, when I run locally, with ./manage.py runserver, it uses the .env file and connects to the db container properly at 127.0.0.1:5342
But if I run docker-compose up web, even though it also read the .env file, the environment variable provided in the compose file takes precedent and it uses POSTGRES_HOST: db and connects to the db container as well!