Docker Compose - How to store database data?

Question

I am new to docker and developing a project using docker compose. From the documentation I have learned that I should be using data only containers to keep data persistant but I am unable to do so using docker-compose. Whenever I do docker-compose down it removes the the data from db but by doing docker-compose stop the data is not removed. May be this is because that I am not creating named data volume and docker-compose down hardly removes all the containers. So I tried naming the container but it threw me errors. Please have a look at my yml file:

version: '2'
services: 
   data_container:
     build: ./data
     #volumes:
     #  - dataVolume:/data
  db:
    build: ./db
    ports:
      - "5445:5432"
    environment:
      - POSTGRES_USER=postgres
      - POSTGRES_DB=postgres
    #   - PGDATA=/var/lib/postgresql/data/pgdata
    volumes_from:
     # - container:db_bus
       - data_container
  geoserver:
    build: ./geoserver
    depends_on:
      - db
    ports:
      - "8004:8080"
    volumes:
      - ./geoserver/data:/opt/geoserverdata_dir

  web:
    build: ./web
    volumes:
      - ./web:/code
    ports:
      - "8000:8000"
    depends_on:
      - db
    command: python manage.py runserver 0.0.0.0:8000

  nginx:
    build: ./nginx
    ports:
      - "83:80"
    depends_on:
      - web

The Docker file for the data_container is:

FROM stackbrew/busybox:latest
MAINTAINER Tom Offermann <[email protected]>

# Create data directory
RUN mkdir /data

# Create /data volume
VOLUME /data

I tried this but by doing docker-compose down, the data is lost. I tried naming the data_container as you can see the commented line, it threw me this error:

ERROR: Named volume "dataVolume:/data:rw" is used in service "data_container" but no declaration was found in the volumes section.

So right now what I am doing is I created a stand alone data only named container and put that in the volumes_from value of the db. It worked fine and didn't remove any data even after doing docker-compose down.

My queries:

• What is the best approach to make containers that can store database's data using the docker-compose and to use them properly ?

• My conscious is not agreeing with me on approach that I have opted, the one by creating a stand alone data container. Any thoughts?

Answer 1

docker-compose down

does the following

Stops containers and removes containers, networks, volumes, and images created by up

So the behaviour you are experiencing is expected.

Use docker-compose stop to shutdown containers created with the docker-compose file but not remove their volumes.

Secondly you don't need the data-container pattern in version 2 of docker compose. So remove that and just use

  db:
    ...
    volumes:
       - /var/lib/postgresql/data