moby--moby/docs/extend/index.md

description	keywords	title
Develop and use a plugin with the managed plugin system	API, Usage, plugins, documentation, developer	Managed plugin system

Docker Engine managed plugin system

• Installing and using a plugin
• Developing a plugin

Docker Engine's plugins system allows you to install, start, stop, and remove plugins using Docker Engine. This mechanism is currently only available for volume drivers, but more plugin driver types will be available in future releases.

For information about the legacy plugin system available in Docker Engine 1.12 and earlier, see Understand legacy Docker Engine plugins.

Note

: Docker Engine managed plugins are currently not supported on Windows daemons.

Installing and using a plugin

Plugins are distributed as Docker images and can be hosted on Docker Hub or on a private registry.

To install a plugin, use the docker plugin install command, which pulls the plugin from Docker hub or your private registry, prompts you to grant permissions or capabilities if necessary, and enables the plugin.

To check the status of installed plugins, use the docker plugin ls command. Plugins that start successfully are listed as enabled in the output.

After a plugin is installed, you can use it as an option for another Docker operation, such as creating a volume.

In the following example, you install the sshfs plugin, verify that it is enabled, and use it to create a volume.

1. Install the sshfs plugin.

   $ docker plugin install vieux/sshfs
   
   Plugin "vieux/sshfs" is requesting the following privileges:
   - network: [host]
   - capabilities: [CAP_SYS_ADMIN]
   Do you grant the above permissions? [y/N] y
   
   vieux/sshfs
   

   The plugin requests 2 privileges:

   • It needs access to the host network.
   • It needs the CAP_SYS_ADMIN capability, which allows the plugin to run the mount command.

2. Check that the plugin is enabled in the output of docker plugin ls.

   $ docker plugin ls
   
   ID                    NAME                  TAG                 DESCRIPTION                   ENABLED
   69553ca1d789          vieux/sshfs           latest              the `sshfs` plugin            true
   

3. Create a volume using the plugin. This example mounts the /remote directory on host 1.2.3.4 into a volume named sshvolume. This volume can now be mounted into containers.

   $ docker volume create \
     -d vieux/sshfs \
     --name sshvolume \
     -o sshcmd=user@1.2.3.4:/remote
   
   sshvolume
   

4. Verify that the volume was created successfully.

   $ docker volume ls
   
   DRIVER              NAME
   vieux/sshfs         sshvolume
   

5. Start a container that uses the volume sshvolume.

   $ docker run -v sshvolume:/data busybox ls /data
   
   <content of /remote on machine 1.2.3.4>
   

To disable a plugin, use the docker plugin disable command. To completely remove it, use the docker plugin remove command. For other available commands and options, see the command line reference.

Service creation using plugins

In swarm mode, it is possible to create a service that allows for attaching to networks or mounting volumes. Swarm schedules services based on plugin availability on a node. In this example, a volume plugin is installed on a swarm worker and a volume is created using the plugin. In the manager, a service is created with the relevant mount options. It can be observed that the service is scheduled to run on the worker node with the said volume plugin and volume.

In the following example, node1 is the manager and node2 is the worker.

1. Prepare manager. In node 1:

   $ docker swarm init
   Swarm initialized: current node (dxn1zf6l61qsb1josjja83ngz) is now a manager.
   

2. Join swarm, install plugin and create volume on worker. In node 2:

   $ docker swarm join \
   --token SWMTKN-1-49nj1cmql0jkz5s954yi3oex3nedyz0fb0xx14ie39trti4wxv-8vxv8rssmk743ojnwacrr2e7c \
   192.168.99.100:2377
   

   $ docker plugin install tiborvass/sample-volume-plugin
   latest: Pulling from tiborvass/sample-volume-plugin
   eb9c16fbdc53: Download complete
   Digest: sha256:00b42de88f3a3e0342e7b35fa62394b0a9ceb54d37f4c50be5d3167899994639
   Status: Downloaded newer image for tiborvass/sample-volume-plugin:latest
   Installed plugin tiborvass/sample-volume-plugin
   

   $ docker volume create -d tiborvass/sample-volume-plugin --name pluginVol
   

3. Create a service using the plugin and volume. In node1:

   $ docker service create --name my-service --mount type=volume,volume-driver=tiborvass/sample-volume-plugin,source=pluginVol,destination=/tmp busybox top
   
   $ docker service ls
   z1sj8bb8jnfn  my-service   replicated  1/1       busybox:latest 
   

   docker service ls shows service 1 instance of service running.

4. Observe the task getting scheduled in node 2:

   $ docker ps --format '{{.ID}}\t {{.Status}} {{.Names}} {{.Command}}' 
   83fc1e842599     Up 2 days my-service.1.9jn59qzn7nbc3m0zt1hij12xs "top"
   

Developing a plugin

The rootfs directory

The rootfs directory represents the root filesystem of the plugin. In this example, it was created from a Dockerfile:

Note: The /run/docker/plugins directory is mandatory inside of the plugin's filesystem for docker to communicate with the plugin.

$ git clone https://github.com/vieux/docker-volume-sshfs
$ cd docker-volume-sshfs
$ docker build -t rootfsimage .
$ id=$(docker create rootfsimage true) # id was cd851ce43a403 when the image was created
$ sudo mkdir -p myplugin/rootfs
$ sudo docker export "$id" | sudo tar -x -C myplugin/rootfs
$ docker rm -vf "$id"
$ docker rmi rootfsimage

The config.json file

The config.json file describes the plugin. See the plugins config reference.

Consider the following config.json file.

{
	"description": "sshFS plugin for Docker",
	"documentation": "https://docs.docker.com/engine/extend/plugins/",
	"entrypoint": ["/go/bin/docker-volume-sshfs"],
	"network": {
		   "type": "host"
		   },
	"interface" : {
		   "types": ["docker.volumedriver/1.0"],
		   "socket": "sshfs.sock"
	},
	"capabilities": ["CAP_SYS_ADMIN"]
}

This plugin is a volume driver. It requires a host network and the CAP_SYS_ADMIN capability. It depends upon the /go/bin/docker-volume-sshfs entrypoint and uses the /run/docker/plugins/sshfs.sock socket to communicate with Docker Engine. This plugin has no runtime parameters.

Creating the plugin

A new plugin can be created by running docker plugin create <plugin-name> ./path/to/plugin/data where the plugin data contains a plugin configuration file config.json and a root filesystem in subdirectory rootfs.

After that the plugin <plugin-name> will show up in docker plugin ls. Plugins can be pushed to remote registries with docker plugin push <plugin-name>.