costela/docker-volume-hetzner repository overview

⁠Docker Volume Plugin for Hetzner Cloud

This plugin manages docker volumes using Hetzner Cloud's volumes.

This plugin is still in ALPHA; use at your own risk

⁠Installation

To install the plugin, run the following command:

$ docker plugin install --alias hetzner costela/docker-volume-hetzner

When using docker swarm, this should be done on all nodes in the cluster.

Important: the plugin expects the docker node's hostname to match with the name of the server created on Hetzner Cloud. This should usually be the case, unless explicitly changed.

⁠Plugin privileges

During installation, you will be prompted to accept the plugins's privilege requirements. The following are required:

• network: used for communicating with the Hetzner Cloud API
• mount[/dev/]: needed for accessing the Hetzner Cloud Volumes (made available to the host as a SCSI device)
• allow-all-devices: actually enable access to the volume devices mentioned above (since the devices cannot be known a priori)
• capabilities[CAP_SYS_ADMIN]: needed for running mount

⁠Usage

The plugin is used by setting the driver option on the docker volume definition (assuming the alias passed during installation above):

volumes:
  somevolume:
    driver: hetzner

This will:

1. If the volume is new in the cluster:
   1. create the Hetzner Cloud volume upon creation of the named volume
   2. attach the created volume to the current node
   3. format the volume (using fstype; see below)
2. mount the volume on the node running its parent service

⁠Configuration

The following options can be passed to the plugin via docker plugin set (all names case-sensitive):

• apikey (required): authentication token to use when accessing the Hetzner Cloud API
• location (required): location in which to create volumes (see also "limitations" below)
• size (optional): size of the volume in GB (default: 10)
• fstype (optional): filesystem type to be created on new volumes. Currently supported values are ext{2,3,4} and xfs (default: ext4)
• prefix (optional): prefix to use when naming created volumes (default: docker)
• loglevel (optional): the amount of information that will be output by the plugin. Accepts any value supported by logrus⁠ (default: warn)

Additionally, location, size and fstype can also be passed as options to the driver:

volumes:
  somevolume:
    driver: hetzner
    driver_opts:
      location: nbg1
      size: '42'
      fstype: xfs

⁠Limitations

• Concurrent use: Hetzner Cloud volumes currently cannot be attached to multiple nodes, so the same limitation applies to the docker volumes using them. This also precludes concurrent use by multiple containers on the same node, since there is currently no way to enforce docker swarm services to be managed together (cf. kubernetes pods).
• Single location: since volumes are currently bound to the location they were created in, this plugin will not be able to attach volumes if you have a swarm cluster across locations and a service migrates over the location boundary.
• Volume resizing: docker has no support for updating volume definitions. After a volume is created, its size option is currently ignored. This may be worked around in a future release.
• Docker partitions: when used in a docker swarm setup, there is a chance a network hiccup between docker nodes might be seen as a node down, in which case the scheduler will start the container on a different node and will "steal" its volume while in use, potentially causing data loss.