Volume plugin for Amazon EBS

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A proof-of-concept Rexray plugin

In this example, a simple Rexray plugin will be created for the purposes of using it on an Amazon EC2 instance with EBS. It is not meant to be a complete Rexray plugin.

The example source is available at https://github.com/tiborvass/rexray-plugin.

To learn more about Rexray: https://github.com/codedellemc/rexray

1. Make a Docker image

The following is the Dockerfile used to containerize rexray.

FROM debian:jessie
RUN apt-get update && apt-get install -y --no-install-recommends wget ca-certificates
RUN wget https://dl.bintray.com/emccode/rexray/stable/0.6.4/rexray-Linux-x86_64-0.6.4.tar.gz -O rexray.tar.gz && tar -xvzf rexray.tar.gz -C /usr/bin && rm rexray.tar.gz
RUN mkdir -p /run/docker/plugins /var/lib/libstorage/volumes
ENTRYPOINT ["rexray"]
CMD ["--help"]

To build it you can run image=$(cat Dockerfile | docker build -q -) and $image will reference the containerized rexray image.

2. Extract rootfs

$ TMPDIR=/tmp/rexray  # for the purpose of this example
$  # create container without running it, to extract the rootfs from image
$ docker create --name rexray "$image"
$  # save the rootfs to a tar archive
$ docker export -o $TMPDIR/rexray.tar rexray
$  # extract rootfs from tar archive to a rootfs folder
$ ( mkdir -p $TMPDIR/rootfs; cd $TMPDIR/rootfs; tar xf ../rexray.tar )

3. Add plugin configuration

We have to put the following JSON to $TMPDIR/config.json:

{
      "Args": {
        "Description": "",
        "Name": "",
        "Settable": null,
        "Value": null
      },
      "Description": "A proof-of-concept EBS plugin (using rexray) for Docker",
      "Documentation": "https://github.com/tiborvass/rexray-plugin",
      "Entrypoint": [
        "/usr/bin/rexray", "service", "start", "-f"
      ],
      "Env": [
        {
          "Description": "",
          "Name": "REXRAY_SERVICE",
          "Settable": [
            "value"
          ],
          "Value": "ebs"
        },
        {
          "Description": "",
          "Name": "EBS_ACCESSKEY",
          "Settable": [
            "value"
          ],
          "Value": ""
        },
        {
          "Description": "",
          "Name": "EBS_SECRETKEY",
          "Settable": [
            "value"
          ],
          "Value": ""
        }
      ],
      "Interface": {
        "Socket": "rexray.sock",
        "Types": [
          "docker.volumedriver/1.0"
        ]
      },
      "Linux": {
        "AllowAllDevices": true,
        "Capabilities": ["CAP_SYS_ADMIN"],
        "Devices": null
      },
      "Mounts": [
        {
          "Source": "/dev",
          "Destination": "/dev",
          "Type": "bind",
          "Options": ["rbind"]
        }
      ],
      "Network": {
        "Type": "host"
      },
      "PropagatedMount": "/var/lib/libstorage/volumes",
      "User": {},
      "WorkDir": ""
}

Please note a couple of points: - PropagatedMount is needed so that the docker daemon can see mounts done by the rexray plugin from within the container, otherwise the docker daemon is not able to mount a docker volume. - The rexray plugin needs dynamic access to host devices. For that reason, we have to give it access to all devices under /dev and set AllowAllDevices to true for proper access. - The user of this simple plugin can change only 3 settings: REXRAY_SERVICE, EBS_ACCESSKEY and EBS_SECRETKEY. This is because of the reduced scope of this plugin. Ideally other rexray parameters could also be set.

4. Create plugin

docker plugin create tiborvass/rexray-plugin "$TMPDIR" will create the plugin.

$ docker plugin ls
ID                  NAME                             DESCRIPTION                         ENABLED
2475a4bd0ca5        tiborvass/rexray-plugin:latest   A rexray volume plugin for Docker   false

5. Test plugin

$ docker plugin set tiborvass/rexray-plugin EBS_ACCESSKEY=$AWS_ACCESSKEY EBS_SECRETKEY=$AWS_SECRETKEY`
$ docker plugin enable tiborvass/rexray-plugin
$ docker volume create -d tiborvass/rexray-plugin my-ebs-volume
$ docker volume ls
DRIVER                              VOLUME NAME
tiborvass/rexray-plugin:latest      my-ebs-volume
$ docker run --rm -v my-ebs-volume:/volume busybox sh -c 'echo bye > /volume/hi'
$ docker run --rm -v my-ebs-volume:/volume busybox cat /volume/hi
bye

6. Push plugin

First, ensure you are logged in with docker login. Then you can run: docker plugin push tiborvass/rexray-plugin to push it like a regular docker image to a registry, to make it available for others to install via docker plugin install tiborvass/rexray-plugin EBS_ACCESSKEY=$AWS_ACCESSKEY EBS_SECRETKEY=$AWS_SECRETKEY.

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