This is a volume plugin for Docker, allowing Docker containers to enjoy persistent volumes residing on ploop, either locally or on the distributed Virtuozzo Storage file system.

Prerequisites

To use this plugin with Virtuozzo Storage, you need to have it up and running.

Alternatively, to use this plugin with ploop, you need to have Virtuozzo or OpenVZ up and running.

Surely, you need Docker up and running. Docker 1.10+ is required, Docker 1.12+ is recommended.

Installation

This guide assumes you are using a recent version of Virtuozzo, Virtuozzo Storage, or OpenVZ, and already have Docker up and running.

The recommended way of installation is from the repository. This is as easy as:

wget https://goo.gl/9N6lfJ -O /etc/yum.repos.d/docker-volume-ploop.repo
yum install docker-volume-ploop

Alternatively, you can build the plugin from source, for details, see INSTALL.md.

Starting

First, you need to set home path for the plugin. To do so, edit the /etc/sysconfig/docker-volume-plugin file, uncommenting the DKV_PLOOP_HOME= line, and modifying the -home argument, for example:

# Set the plugin home directory
DKV_PLOOP_HOME="-home /mnt/vstorage/docker/"

Now you can start a daemon:

systemctl start docker-volume-ploop

Usage

Once docker and docker-volume-ploop are running, you can create a volume:

docker volume create -d ploop -o size=512G --name MyFirstVolume

To run a container with the volume:

docker run -it -v VOLUME:/MOUNT alpine /bin/ash

Here VOLUME is the volume name, and MOUNT is the path under which the volume will be available inside a container. For example:

docker run -it -v MyFirstVol:/mnt alpine /bin/ash

See man docker volume for other volume operations. For example, to list existing volumes:

docker volume ls

Troubleshooting

Docker with Virtuozzo/OpenVZ kernel

For Docker to work, you need to make sure conntracks are enabled on the host. In case it's not done, docker might complain like this:

Error starting daemon: Error initializing network controller: error obtaining controller instance: failed to create NAT chain: iptables failed: iptables --wait -t nat -N DOCKER: iptables v1.4.21: can't initialize iptables table `nat': Table does not exist (do you need to insmod?)\nPerhaps iptables or your kernel needs to be upgraded.\n (exit status 3)

To fix, edit /etc/modprobe.d/parallels.conf (or /etc/modprobe.d/openvz.conf) to look like this:

options nf_conntrack ip_conntrack_disable_ve0=0

In other words, the value should be set to 0. After making the change, reboot the machine.

Miscellaneous ploop operations

The following is the quick introduction of what operations can be performed with ploop images. For more detailed information about ploop, see openvz.org/Ploop.

Use ploop command line tool, and refer to an image by path to DiskDescriptor.xml file. This driver creates images under img subdirectory of its home. So, to use the following commands, you need to cd to the image directory, for example:

cd /pcs/img/MyFirstVol/

Snapshots

To create a snapshot:

ploop snapshot DiskDescriptor.xml

To list snapshots:

ploop snapshot-list DiskDescriptor.xml

To delete a snapshot:

ploop snapshot-delete -u UUID DiskDescriptor.xml

To mount a snapshot (read-only):

ploop mount -r -u UUID -m MOUNT_POINT DiskDescriptor.xml

Resizing

To resize an image (can be done while it's running):

ploop resize -s SIZE DiskDescriptor.xml

Checking

In case something is wrong (ploop image can't be mounted etc.), you might want to check it.

ploop check DiskDescriptor.xml

If you want to run fsck on an inner filesystem, you can use the following command:

ploop mount -F DiskDescriptor.xml

Don't forget to unmount it:

ploop umount DiskDescriptor.xml

Licensing

This software is licensed under the Apache License, Version 2.0. See LICENSE for the full license text.