Ceph Rados Block Device Docker VolumeDriver Plugin

• Use Case: Persistent Storage for a Single Docker Container

  • an RBD Image can only be used by 1 Docker Container at a time

• Plugin is a separate process running alongside Docker Daemon

  • plugin can only be configured for a single Ceph User (currently no good way to pass things from docker -> plugin, get only volume name)
  • run multiple plugin instances for varying configs (ceph user, default pool, default size)
  • can pass extra config via volume name to override default pool and creation size:
    • docker run --volume-driver rbd -v poolname/imagename@size:/mnt/disk1 ...

• plugin supports all Docker VolumeDriver Plugin API commands:

  • Create - can provision Ceph RBD Image in a pool of a certain size
    • controlled by --create boolean flag (default false)
    • default size from --size flag (default 20480 = 20GB)
  • Mount - Locks, Maps and Mounts RBD Image to the Host system
  • Unmount - Unmounts, Unmaps and Unlocks the RBD Image on request
  • Remove - Removes (destroys) RBD Image on request
    • only called for docker run --rm -v ... or docker rm -v ...
    • action controlled by plugin's --remove flag, which can be one of three values:
      • ''ignore'' - the call to delete the ceph rbd volume is ignored (default)
      • ''rename'' - will cause image to be renamed with zz prefix for later culling
      • ''delete'' - will actually delete ceph rbd image (destructive)
  • Get, List

Plugin Setup

Plugin is a standalone process and places a Socket file in a known location. Generally need to start this before running Docker. It does not daemonize as it is expected to be controlled by systemd, so if you need it in the background, use normal shell process control (&).

The socket has a name (sans .sock) which is used to refer to the plugin via the --volume-driver=name docker CLI option, allowing multiple uniquely named plugin instances with different default configurations.

The default name for the socket is "rbd", so you would refer to --volume-driver rbd from docker.

General build/run requirements:

• librados2-devel and librbd1-devel for go-ceph
• /usr/bin/rbd for mapping and unmapping to kernel
• /usr/sbin/mkfs.xfs for fs creation
• /usr/bin/mount and /usr/bin/umount

Tested with Ceph version 0.94.2 on Centos 7.1 host with Docker 1.8.

Commandline Options

Usage of ./rbd-docker-plugin:
  --ceph-user="admin": Ceph user to use for RBD
  --create=false: Can auto Create RBD Images (default: false)
  --fs="xfs": FS type for the created RBD Image (must have mkfs.type)
  --logdir="/var/log": Logfile directory for RBD Docker Plugin
  --mount="/var/lib/docker/volumes": Mount directory for volumes on host
  --name="rbd": Docker plugin name for use on --volume-driver option
  --plugin-dir="/run/docker/plugins": Docker plugin directory for socket
  --pool="rbd": Default Ceph Pool for RBD operations
  --remove=false: Can Remove (destroy) RBD Images (default: false, volume will be renamed zz_name)
  --size=20480: RBD Image size to Create (in MB) (default: 20480=20GB

Running Plugin

Start with the default options:

• socket name=rbd, pool=rbd, user=admin, logfile=/var/log/rbd-docker-plugin.log

• no creation or removal of volumes

  sudo rbd-docker-plugin

  docker run --volume-driver rbd -v ...

For Debugging: send log to STDERR:

sudo RBD_DOCKER_PLUGIN_DEBUG=1 rbd-docker-plugin

Use a different socket name and Ceph pool

sudo rbd-docker-plugin --name rbd2 --pool liverpool
# docker run --volume-driver rbd2 -v ...

To allow creation of new RBD Images:

sudo rbd-docker-plugin --create

To allow creation and removal:

sudo rbd-docker-plugin --create --remove

Testing

Use with docker 1.8+ which has the --volume-driver support.

• https://docker.com/

Alternatively, you can POST json to the socket to test the functionality manually. If your curl is new enough (v7.40+), you can use the --unix-socket option and syntax. You can also use this golang version instead:

go get github.com/Soulou/curl-unix-socket

Once you have that you can POST json to the plugin:

% sudo curl-unix-socket -v -X POST unix:///run/docker/plugins/rbd.sock:/Plugin.Activate
> POST /Plugin.Activate HTTP/1.1
> Socket: /run/docker/plugins/rbd.sock
> Content-Length: 0
>
< HTTP/1.1 200 OK
< Content-Type: appplication/vnd.docker.plugins.v1+json
< Date: Tue, 28 Jul 2015 18:52:11 GMT
< Content-Length: 33
{"Implements": ["VolumeDriver"]}


# Plugin started without --create:
% sudo curl-unix-socket -v -X POST -d '{"Name": "testimage"}' unix:///run/docker/plugins/rbd.sock:/VolumeDriver.Create
> POST /VolumeDriver.Create HTTP/1.1
> Socket: /run/docker/plugins/rbd.sock
> Content-Length: 21
>
< HTTP/1.1 500 Internal Server Error
< Content-Length: 62
< Content-Type: appplication/vnd.docker.plugins.v1+json
< Date: Tue, 28 Jul 2015 18:53:20 GMT
{"Mountpoint":"","Err":"Ceph RBD Image not found: testimage"}

# Plugin started --create turned on will create unknown image:
% sudo curl-unix-socket -v -X POST -d '{"Name": "testimage"}' unix:///run/docker/plugins/rbd.sock:/VolumeDriver.Create
> POST /VolumeDriver.Create HTTP/1.1
> Socket: /run/docker/plugins/rbd.sock
> Content-Length: 21
>
< HTTP/1.1 200 OK
< Content-Length: 27
< Content-Type: appplication/vnd.docker.plugins.v1+json
< Date: Fri, 14 Aug 2015 19:47:35 GMT
{"Mountpoint":"","Err":""}

Examples

If you need persistent storage for your application container, you can use a Ceph Block Device as a persistent disk.

You can provision the Block Device and Filesystem first, or allow a sufficiently configured Plugin instance create it for you. This plugin can create RBD images with XFS filesystem.

1. (Optional) Provision RBD Storage yourself

• sudo rbd create --size 1024 foo
• sudo rbd map foo => /dev/rbd1
• sudo mkfs.xfs /dev/rbd1
• sudo rbd unmap /dev/rbd1

2. Or Run the RBD Docker Plugin with --create option flag

• sudo rbd-docker-plugin --create

3. Requesting and Using Storage

• docker run --volume-driver=rbd --volume foo:/mnt/foo -it ubuntu /bin/bash
• Volume will be locked, mapped and mounted to Host and bind-mounted to container at /mnt/foo
• When container exits, the volume will be unmounted, unmapped and unlocked
• You can control the RBD Pool and initial Size using this syntax:
  • foo@1024 => pool=rbd (default), image=foo, size 1GB
  • deep/foo => pool=deep, image=foo and default --size (20GB)
  • deep/foo@1024 => pool=deep, image=foo, size 1GB
  • pool must already exist

Misc

• RBD Snapshots: sudo rbd snap create --image foo --snap foosnap
• Resize RBD image:
  • set max size: sudo rbd resize --size 2048 --image foo
  • map/mount and then fix XFS: sudo xfs_growfs -d /mnt/foo

TODO

• add cluster config options to support non-default clusters
• figure out how to test
  • do we need a working ceph cluster?
  • docker containers with ceph?

Links

Docker API Documentation

• Experimental: Extend Docker with a Plugin
• Experimental: Docker Plugin API
• Experimental: Docker Volume Plugins

Code Examples and Libraries

• https://plugins-demo-2015.github.io
• Flocker Docker Plugin
• VolumeDriver golang framework: https://github.com/docker/go-plugins-helpers/tree/master/volume
• GlusterFS Example: https://github.com/calavera/docker-volume-glusterfs
• KeyWhiz example: https://github.com/calavera/docker-volume-keywhiz
• Ceph Rados, RBD golang lib: https://github.com/ceph/go-ceph

Related Projects

• https://github.com/AcalephStorage/docker-volume-ceph-rbd
• https://github.com/contiv/volplugin

Packaging

Using tpkg package to distribute and specify native package dependencies. Tested with Centos 7.1 and yum/rpm packages.

License

This project is using the MIT License (MIT), see LICENSE file.

Copyright (c) 2015 YP LLC