How to make volumes permanent with Docker Compose v2

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庸人自扰
庸人自扰 2021-02-02 13:19

I realize other people have had similar questions but this uses v2 compose file format and I didn\'t find anything for that.

I want to make a very simple test a

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  • 2021-02-02 13:46

    I realize this is an old and solved thread where the OP was pointing to a directory in the container rather than the volume they had mounted, but wanted to clear up some of the misinformation I'm seeing.

    docker-compose down does not remove volumes, you need to run docker-compose down -v if you also want to delete volumes. Here's the help text straight from docker-compose (note the "by default" list):

    $ docker-compose down --help
    Stops containers and removes containers, networks, volumes, and images
    created by `up`.
    
    By default, the only things removed are:
    
    - Containers for services defined in the Compose file
    - Networks defined in the `networks` section of the Compose file
    - The default network, if one is used
    
    Networks and volumes defined as `external` are never removed.
    
    Usage: down [options]
    
    Options:
    ...
        -v, --volumes       Remove named volumes declared in the `volumes` section
                            of the Compose file and anonymous volumes
                            attached to containers.
    ...
    
    $ docker-compose --version
    docker-compose version 1.12.0, build b31ff33
    

    Here's a sample yml with a named volume to test and a dummy command:

    $ cat docker-compose.vol-named.yml
    version: '2'
    
    volumes:
      data:
    
    services:
      test:
        image: busybox
        command: tail -f /dev/null
        volumes:
        - data:/data
    
    $ docker-compose -f docker-compose.vol-named.yml up -d
    Creating volume "test_data" with default driver
    Creating test_test_1
    

    After starting the container, the volume is initialized empty since the image is empty at that location. I created a quick hello world in that location:

    $ docker exec -it test_test_1 /bin/sh
    / # ls -al /data
    total 8
    drwxr-xr-x    2 root     root          4096 May 23 01:24 .
    drwxr-xr-x    1 root     root          4096 May 23 01:24 ..
    / # echo "hello volume" >/data/hello.txt
    / # ls -al /data
    total 12
    drwxr-xr-x    2 root     root          4096 May 23 01:24 .
    drwxr-xr-x    1 root     root          4096 May 23 01:24 ..
    -rw-r--r--    1 root     root            13 May 23 01:24 hello.txt
    / # cat /data/hello.txt
    hello volume
    / # exit
    

    The volume is visible outside of docker and is still there after a docker-compose down:

    $ docker volume ls | grep test_
    local               test_data
    
    $ docker-compose -f docker-compose.vol-named.yml down
    Stopping test_test_1 ... done
    Removing test_test_1 ... done
    Removing network test_default
    
    $ docker volume ls | grep test_
    local               test_data
    

    Recreating the container uses the old volume with the file still visible inside:

    $ docker-compose -f docker-compose.vol-named.yml up -d
    Creating network "test_default" with the default driver
    Creating test_test_1
    
    $ docker exec -it test_test_1 /bin/sh
    / # cat /data/hello.txt
    hello volume
    / # exit
    

    And running a docker-compose down -v finally removes both the container and the volume:

    $ docker-compose -f docker-compose.vol-named.yml down -v
    Stopping test_test_1 ... done
    Removing test_test_1 ... done
    Removing network test_default
    Removing volume test_data
    
    $ docker volume ls | grep test_
    
    $
    

    If you find your data is only being persisted if you use a stop/start rather than a down/up, then your data is being stored in the container (or possibly an anonymous volume) rather than your named volume, and the container is not persistent. Make sure the location for your data inside the container is correct to avoid this.

    To debug where data is being stored in your container, I'd recommend using docker diff on a container. That will show all of the files created, modified, or deleted inside that container which will be lost when the container is deleted. E.g.:

    $ docker run --name test-diff busybox \
      /bin/sh -c "echo hello docker >/etc/hello.conf"
    
    $ docker diff test-diff
    C /etc
    A /etc/hello.conf
    
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  • 2021-02-02 13:52

    You are using docker-compose down and if you look at the docs here

    Stop containers and remove containers, networks, volumes, and images created by up. Only containers and networks are removed by default.

    You are right, it should not remove volumes (by default). It may be a bug or you may have changed the default configuration. But I think the right command for you is docker-compose stop. I will try to make some tests with simplier cases for down command.

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  • 2021-02-02 13:57

    This was traced back to a bad documentation from MemSQL. MemSQL data path in memsql/quickstart container is /memsql and not /var/lib/memsql like in a stand-alone installation (and in MemSQL docs), and definitely not /data like somebody told me.

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  • 2021-02-02 13:57

    Not sure if this helps or not. When you use docker-compose up -d the container is downloaded and images created. To stop the docker images, use docker-compose down, and the images will remain and can be restarted with docker-compose start

    I was using the up/down commands and kept losing my data until I tried the stop/start and now data persists.

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  • 2021-02-02 13:59

    The simplest solution is to use docker-compose stop instead of docker-compose down. And then docker-compose start to restart.

    According to the docs, down "stops containers and removes containers, networks, volumes, and images created by up."

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