As of Docker Compose 1.6, there is now improved support for data volumes in Docker Compose. The following compose file will create a data image which will persist between restarts (or even removal) of parent containers:
Here is the blog announcement: Compose 1.6: New Compose file for defining networks and volumes
Here's an example compose file:
version: "2"
services:
db:
restart: on-failure:10
image: postgres:9.4
volumes:
- "db-data:/var/lib/postgresql/data"
web:
restart: on-failure:10
build: .
command: gunicorn mypythonapp.wsgi:application -b :8000 --reload
volumes:
- .:/code
ports:
- "8000:8000"
links:
- db
volumes:
db-data:
As far as I can understand: This will create a data volume container (db_data) which will persist between restarts.
If you run: docker volume ls you should see your volume listed:
local mypthonapp_db-data
...
You can get some more details about the data volume:
docker volume inspect mypthonapp_db-data
[
{
"Name": "mypthonapp_db-data",
"Driver": "local",
"Mountpoint": "/mnt/sda1/var/lib/docker/volumes/mypthonapp_db-data/_data"
}
]
Some testing:
# Start the containers
docker-compose up -d
# .. input some data into the database
docker-compose run --rm web python manage.py migrate
docker-compose run --rm web python manage.py createsuperuser
...
# Stop and remove the containers:
docker-compose stop
docker-compose rm -f
# Start it back up again
docker-compose up -d
# Verify the data is still there
...
(it is)
# Stop and remove with the -v (volumes) tag:
docker-compose stop
docker=compose rm -f -v
# Up again ..
docker-compose up -d
# Check the data is still there:
...
(it is).
Notes:
You can also specify various drivers in the volumes block. For example, You could specify the Flocker driver for db_data:
volumes:
db-data:
driver: flocker
Disclaimer: This approach is promising, and I'm using it successfully in a development environment. I would be apprehensive to use this in production just yet!