This package provides a Docker volume plugin that creates a BTRFS subvolume for each container volume.
Please note this is not a BTRFS storage driver for Docker, but a plugin to manage only volumes. It means you can use any storage driver, such as AUFS, this is independant topic.
Contents
- BTRFS Volume plugin for Docker
- Introduction
- Build
- Install and run
- Usage
- Running the plugin
- Creating and deleting volumes
- Managing volumes and snapshots
- Create a snapshot
- List the snapshots
- Restore a snapshot
- Clone a volume
- Delete a snapshot
- Replicate a snapshot to another host
- Synchronize a volume from another host volume
- Purge old snapshots
- Schedule a job
- List scheduled jobs
- Disabling copy-on-write
- Test
- Credits
BTRFS is a next-generation copy-on-write filesystem with subvolume and snapshot support. A BTRFS subvolume can be seen as an independant file namespace that can live in a directory and can be mounted as a filesystem and snapshotted individually.
On the other hand, Docker volumes are commonly used to store persistent data of stateful containers, such as a MySQL/PostgreSQL database or an upload directory of a CMS. By default, Docker volumes are just a dumb directory in the host filesystem. A number of Volume plugins already exist for various storage backends, including distributed filesystems, but small clusters often can't afford to deploy a distributed filesystem.
We believe BTRFS subvolumes are a powerful and lightweight storage solution for Docker volumes, allowing fast and easy replication (and backup) across several nodes of a small cluster.
You can build a docker image with the provided Dockerfile:
$ cd docker $ docker build -t buttervolume .
Make sure the directory /var/lib/docker/volumes
is living in a BTRFS
filesystem. It can be a BTRFS mountpoint or a BTRFS subvolume or both.
You should also create the directory for the unix socket of the plugin:
$ sudo mkdir /run/docker/plugins
Then create a container for buttervolume with access to the host volumes and the unix socket
Either from the image you just built:
$ sudo docker create --privileged -v /var/lib/docker:/var/lib/docker -v /run/docker/plugins/:/run/docker/plugins/ --name buttervolume buttervolume $ docker start buttervolume
Or directly by pulling a prebaked image from the Docker hub:
$ docker run --privileged -v /var/lib/docker/volumes:/var/lib/docker/volumes -v /run/docker/plugins:/run/docker/plugins anybox/buttervolume
You can also locally install and run the plugin with:
$ virtualenv venv $ ./venv/bin/python setup.py develop $ sudo ./venv/bin/buttervolume run
If you installed it locally, You can start the plugin with:
$ sudo buttervolume run
If you're running it in a privileged container, it will be automatically started.
When started it will create a unix socket /var/run/docker/plugins/btrfs.sock
for use by
Docker. The name of the socket file is actually the name of the plugin you can
use with docker volume create -d <driver>
or docker create --volume-driver=<driver>
. when started, the plugin will also start
its own scheduler to run periodic jobs (such as a snapshot, replication, purge or synchronization)
Once the plugin is running, whenever you create a container you can specify the
volume driver with docker create --volume-driver=btrfs --name <name>
<image>
. You can also manually create a BTRFS volume with docker volume
create -d btrfs
. It also works with docker-compose, by specifying the
btrfs
driver in the volumes
section of the compose file.
When you delete the volume with docker rm -v <container>
or docker volume
rm <volume>
, the BTRFS subvolume is deleted. If you snapshotted the volume
elsewhere in the meantime, the snapshots won't be deleted.
When buttervolume is installed, it provides a command line tool
buttervolume
, with the following subcommands:
run Run the plugin in foreground snapshot Snapshot a volume snapshots List snapshots schedule (un)Schedule a snapshot, replication or purge scheduled List scheduled actions restore Restore a snapshot (optionally to a different volume) clone Clone a volume as new volume send Send a snapshot to another host sync Synchronise a volume from a remote host volume rm Delete a snapshot purge Purge old snapshot using a purge pattern
You can create a readonly snapshot of the volume with:
$ buttervolume snapshot <volume>
The volumes are currently expected to live in /var/lib/docker/volumes
and
the snapshot will be created in /var/lib/docker/snapshots
, by appending the
datetime to the name of the volume, separated with @
.
You can list all the snapshots:
$ buttervolume snapshots
or just the snapshots corresponding to a volume with:
$ buttervolume snapshots <volume>
<volume>
is the name of the volume, not the full path. It is expected
to live in /var/lib/docker/volumes
.
You can restore a snapshot as a volume. The current volume will first be snapshotted, deleted, then replaced with the snapshot. If you provide a volume name instead of a snapshot, the latest snapshot is restored. So no data is lost if you do something wrong. Please take care of stopping the container before restoring a snapshot:
$ buttervolume restore <snapshot>
<snapshot>
is the name of the snapshot, not the full path. It is expected
to live in /var/lib/docker/snapshots
.
By default, the volume name corresponds to the volume the snapshot was created from. But you can optionally restore the snapshot to a different volume name by adding the target as the second argument:
$ buttervolume restore <snapshot> <volume>
You can clone a volume as a new volume. The current volume will be cloned as a new volume name given as parameter. Please take care of stopping the container before clonning a volume:
$ buttervolume clone <volume> <new_volume>
<volume>
is the name of the volume to be cloned, not the full path. It is expected
to live in /var/lib/docker/volumes
.
<new_volume>
is the name of the new volume to be created as clone of previous one,
not the full path. It is expected to be created in /var/lib/docker/volumes
.
You can delete a snapshot with:
$ buttervolume rm <snapshot>
<snapshot>
is the name of the snapshot, not the full path. It is expected
to live in /var/lib/docker/snapshots
.
You can incrementally send snapshots to another host, so that data is replicated to several machines, allowing to quickly move a stateful docker container to another host. The first snapshot is first sent as a whole, then the next snapshots are used to only send the difference between the current one and the previous one. This allows to replicate snapshots very often without consuming a lot of bandwith or disk space:
$ buttervolume send <host> <snapshot>
<snapshot>
is the name of the snapshot, not the full path. It is expected
to live in /var/lib/docker/snapshots
and is replicated to the same path on
the remote host.
<host>
is the hostname or IP address of the remote host. The snapshot is
currently sent using BTRFS send/receive through ssh. This requires that ssh
keys be present and already authorized on the target host, and that the
StrictHostKeyChecking no
option be enabled in ~/.ssh/config
.
You can receive data from a remote volume, so in case there is a volume on
the remote host with the same name, it will get new and most recent data
from the distantant volume and replace in the local volume. Before running the
rsync
command a snapshot is made on the locale machine to manage recovery:
$ buttervolume sync <volume> <host1> [<host2>][...]
The intent is to synchronize a volume between multi hosts on running containers, so you should schedule that action on each nodes from all remote hosts.
Note
As we are pulling data from multiple hosts we never remove data, consider removing scheduled actions before removing data on each hosts.
Warning
Make sure your application is able to handle such synchronisation
You can purge old snapshot corresponding to the specified volume, using a retention pattern:
$ buttervolume purge <pattern> <volume>
If you're unsure whether you retention pattern is correct, you can run the
purge with the --dryrun
option, to inspect what snapshots would be deleted,
without deleting them:
$ buttervolume purge --dryrun <pattern> <volume>
<volume>
is the name of the volume, not the full path. It is expected
to live in /var/lib/docker/volumes
.
<pattern>
is the snapshot retention pattern. It is a semicolon-separated
list of time length specifiers with a unit. Units can be m
for minutes,
h
for hours, d
for days, w
for weeks, y
for years. The pattern
should have at least 2 items.
Here are a few examples of retention patterns:
4h:1d:2w:2y
- Keep all snapshots in the last four hours, then keep only one snapshot every four hours during the first day, then one snapshot per day during the first two weeks, then one snapshot every two weeks during the first two years, then delete everything after two years.
4h:1w
- keep all snapshots during the last four hours, then one snapshot every four hours during the first week, then delete older snapshots.
2h:2h
- keep all snapshots during the last two hours, then delete older snapshots.
You can schedule a periodic job, such as a snapshot, a replication, a
synchronization or a purge. The schedule it self is stored in
/etc/buttervolume/schedule.csv
.
Schedule a snapshot of a volume every 60 minutes:
$ buttervolume schedule snapshot 60 <volume>
Remove the same schedule by specifying a timer of 0 min:
$ buttervolume schedule snapshot 0 <volume>
Schedule a replication of volume foovolume
to remote_host
:
$ buttervolume schedule replicate:remote_host 3600 foovolume
Remove the same schedule:
$ buttervolume schedule replicate:remote_host 0 foovolume
Schedule a purge every hour of the snapshots of volume foovolume
, but
keep all the snapshots in the last 4 hours, then only one snapshot every 4
hours during the first week, then one snapshot every week during one year, then
delete all snapshots after one year:
$ buttervolume schedule purge:4h:1w:1y 60 foovolume
Remove the same schedule:
$ buttervolume schedule purge:4h:1w:1y 0 foovolume
Using the right combination of snapshot schedule timer, purge schedule timer and purge retention pattern, you can create you own backup strategy, from the simplest ones to more elaborate ones. A common one is the following:
$ buttervolume schedule snapshot 1440 <volume> $ buttervolume schedule purge:1d:4w:1y 1440 <volume>
It should create a snapshot every day, then purge snapshots everydays while keeping all snapshots in the last 24h, then one snapshot per day during one month, then one snapshot per month during only one year.
Schedule a syncrhonization of volume foovolume
from remote_host1
abd remote_host2
:
$ buttervolume schedule synchronize:remote_host1,remote_host2 60 foovolume
Remove the same schedule:
$ buttervolume schedule synchronize:remote_host1,remote_host2 0 foovolume
You can list all the scheduled job with:
$ buttervolume scheduled
It will display the schedule in the same format used for adding the schedule, which is convenient to remove an existing schedule or add a similar one.
UPDATE: Copy On Write is disabled by default.
TODO: replace the .nocow file feature with an option to pass
With buttervolume you can disable copy-on-write in a volume by creating a .nocow
file at the
root of the volume. The buttervolume plugin will detect it at mount-time and apply chattr +C
on the volume root.
Why disabling copy-on-write? If your docker volume stores databases such as PostgreSQL or MariaDB, the copy-on-write feature may hurt performance a lot. The good news is that disabling copy-on-write does not prevent from doing snaphots, so we get the best of both world: good performances with the ability to do snapshots.
Creating such a .nocow
file can easily be done in a Dockerfile, before the
VOLUME
command:
RUN mkdir -p /var/lib/postgresql/data \
&& chown -R postgres: /var/lib/postgresql/data \
&& touch /var/lib/postgresql/data/.nocow
VOLUME /var/lib/postgresql/data
Alternatively you can create the .nocow
file just after the docker
create
command, by inspecting the location of the created volumes with
docker inspect container | grep volumes
.
If your volumes directory is a BTRFS partition or volume, tests can be run with:
$ export SSH_PORT=22 # port of your running ssh server with authorized key $ sudo -E python3 setup.py test
or using and testing the docker image (with python >= 3.5):
$ docker build -t anybox/buttervolume docker/ $ sudo docker run -it --rm --privileged \ -v /var/lib/docker:/var/lib/docker \ -v "$PWD":/usr/src/buttervolume \ -w /usr/src/buttervolume \ anybox/buttervolume test
If you have no BTRFS partitions or volumes you can setup a virtual partition in a file as follows (tested on Debian 8):
Setup BTRFS virtual partition:
$ sudo qemu-img create /var/lib/docker/btrfs.img 10G Formatting '/var/lib/docker/btrfs.img', fmt=raw size=10737418240 $ sudo mkfs.btrfs /var/lib/docker/btrfs.img Btrfs v3.17 See http://btrfs.wiki.kernel.org for more information. Turning ON incompat feature 'extref': increased hardlink limit per file to 65536 ERROR: device scan failed '/var/lib/docker/btrfs.img' - Block device required fs created label (null) on /var/lib/docker/btrfs.img nodesize 16384 leafsize 16384 sectorsize 4096 size 10.00GiB
Note
you can ignore the error, in fact the new FS is formatted
Mount the partition somewhere temporarily to create 3 new BTRFS subvolumes:
$ sudo mkdir /tmp/btrfs_mount_point \ && sudo mount -o loop /var/lib/docker/btrfs.img /tmp/btrfs_mount_point/ \ && sudo btrfs subvolume create /tmp/btrfs_mount_point/snapshots \ && sudo btrfs subvolume create /tmp/btrfs_mount_point/volumes \ && sudo btrfs subvolume create /tmp/btrfs_mount_point/received \ && sudo umount /tmp/btrfs_mount_point/ \ && sudo rm -r /tmp/btrfs_mount_point/
Stop docker, create required mount point and restart docker:
$ sudo systemctl stop docker \ && sudo mkdir -p /var/lib/docker/volumes \ && sudo mkdir -p /var/lib/docker/snapshots \ && sudo mkdir -p /var/lib/docker/received \ && sudo mount -o loop,subvol=volumes /var/lib/docker/btrfs.img /var/lib/docker/volumes \ && sudo mount -o loop,subvol=snapshots /var/lib/docker/btrfs.img /var/lib/docker/snapshots \ && sudo mount -o loop,subvol=received /var/lib/docker/btrfs.img /var/lib/docker/received \ && sudo systemctl start docker
once you are done with your test when you can umount those volume and you will find back your previous docker volumes:
$ sudo systemctl stop docker \ && sudo umount /var/lib/docker/volumes \ && sudo umount /var/lib/docker/snapshots \ && sudo umount /var/lib/docker/received \ && sudo systemctl start docker \ && sudo rm /var/lib/docker/btrfs.img
- Christophe Combelles
- Pierre Verkest