local-persist

Local Persist Volume Plugin for Docker

Create named local volumes that persist in the location(s) you want!

Rationale

In Docker 1.9, they added support for creating standalone named Volumes. Now with Docker 1.10 and Docker Compose 1.6's new syntax, you can create named volumes through Docker Compose.

This is great for creating standalone volumes and easily connecting them to different directories in different containers as a way to share data between multiple containers. On a much larger scale, it also allows for the use of Docker Volume Plugins to do cool things like Flocker is doing (help run stateful containers across multiple hosts).

If something like Flocker is overkill for your needs, it can still be useful for

Installing & Running

To create a Docker Plugin, one must create a Unix socket that Docker will look for when you use the plugin and then it listens for commands from Docker and runs the corresponding code when necessary.

Running the code in this project with create the said socket, listening for commands from Docker to create the necessary Volumes.

Pre-1.0, you can either build and run the project locally, or use this with Docker (run this on your Docker host):

docker run -d \
    -v /run/docker/plugins/:/run/docker/plugins/ \
    -v /path/to/where/you/want/data/volume/:/path/to/where/you/want/data/volume/ \ 
        cwspear/docker-local-persist-volume-plugin

The -v /run/docker/plugins/:/run/docker/plugins/ part will make sure the sock file gets created at the right place. You also need to add one or more volumes to places you want to mount your volumes later at.

For example, if I am going to persist my MySQL data for a container I'm going to build later at /data/mysql/, I would add a -v /data/mysql/:/data/mysql/ to the command above (or even -v /data/:/data/).

Usage

Then to use, you can create a volume with this plugin (this example will be for a shared folder for images):

docker create volume create -d local-persist -o mountpoint=/data/images --name=images

Then if you create a container, you can connect it to this Volume:

docker run -d -v images:/path/to/images/on/one/ one
docker run -d -v images:/path/to/images/on/two/ two
# etc

Also, see docker-compose.example.yml for an example to do something like this with Docker Compose (needs Compose 1.6+ and Engine 1.10+).

Benefits

This has a few advantages over the (default) local driver that comes with Docker, because our data will not be deleted when the Volume is removed. The local driver deletes all data when it's removed. With the local-persist driver, if you remove the driver, and then recreate it later with the same command above, any volume that was added to that volume will still be there.

You may have noticed that you could do this with data-only containers, too. And that's true, and using that technique has a few advantages, one thing it (specifically as a limitation of volumes-from) does not allow, is mounting that shared volume to a different path inside your containers. Trying to recreate the above example, each container would have to store images in the same directory in their containers, instead of separate ones which local-persist allows.

Also, using local-persist instead of data-only containers, docker ps -a won't have extra dead entries, and docker volume ls will have more descriptive output (because volumes have names).