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Rewrites to Developing Plugins topic
Signed-off-by: Misty Stanley-Jones <misty@docker.com>
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Misty Stanley-Jones
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@ -1,51 +1,54 @@
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---
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aliases: [
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"/engine/extend/"
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]
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title: "Managed plugin system"
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description: "How develop and use a plugin with the managed plugin system"
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keywords: ["API, Usage, plugins, documentation, developer"]
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advisory: "experimental"
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advisory: experimental
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aliases:
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- /engine/extend/
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description: Develop and use a plugin with the managed plugin system
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keywords:
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- API, Usage, plugins, documentation, developer
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title: Managed plugin system
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---
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<!-- This file is maintained within the docker/docker Github
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repository at https://github.com/docker/docker/. Make all
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pull requests against that repo. If you see this file in
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another repository, consider it read-only there, as it will
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periodically be overwritten by the definitive file. Pull
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requests which include edits to this file in other repositories
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will be rejected.
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-->
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# Docker Engine managed plugin system
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This document describes the plugin system available today in the **experimental
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build** of Docker 1.12:
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* [How to operate an existing plugin](#how-to-operate-a-plugin)
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* [How to develop a plugin](#how-to-develop-a-plugin)
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* [Installing and using a plugin](index.md#installing-and-using-a-plugin)
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* [Developing a plugin](index.md#developing-a-plugin)
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Unlike the legacy plugin system, you now manage plugins using Docker Engine:
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Docker Engine's plugins system allows you to install, start, stop, and remove
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plugins using Docker Engine. This mechanism is currently only available for
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volume drivers, but more plugin driver types will be available in future releases.
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* install plugins
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* start plugins
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* stop plugins
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* remove plugins
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For information about the legacy plugin system available in Docker Engine 1.12
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and earlier, see [Understand legacy Docker Engine plugins](legacy_plugins.md).
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The current Docker Engine plugin system only supports volume drivers. We are
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adding more plugin driver types in the future releases.
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## Installing and using a plugin
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For information on Docker Engine plugins generally available in Docker Engine
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1.12 and earlier, refer to [Understand legacy Docker Engine plugins](legacy_plugins.md).
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Plugins are distributed as Docker images and can be hosted on Docker Hub or on
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a private registry.
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## How to operate a plugin
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To install a plugin, use the `docker plugin install` command, which pulls the
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plugin from Docker hub or your private registry, prompts you to grant
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permissions or capabilities if necessary, and enables the plugin.
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Plugins are distributed as Docker images, so develpers can host them on Docker
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Hub or on a private registry.
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To check the status of installed plugins, use the `docker plugin ls` command.
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Plugins that start successfully are listed as enabled in the output.
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You install the plugin using a single command: `docker plugin install <PLUGIN>`.
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The `plugin install` command pulls the plugin from the Docker Hub or private
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registry. If necessary the CLI prompts you to accept any privilege requriements.
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For example the plugin may require access to a device on the host system.
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Finally it enables the plugin.
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After a plugin is installed, you can use it as an option for another Docker
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operation, such as creating a volume.
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Run `docker plugin ls` to check the status of installed plugins. The Engine
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markes plugins that are started without issues as `ENABLED`.
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After you install a plugin, the plugin behavior is the same as legacy plugins.
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The following example demonstrates how to install the `sshfs` plugin and use it
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to create a volume.
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In the following example, you install the `sshfs` plugin, verify that it is
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enabled, and use it to create a volume.
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1. Install the `sshfs` plugin.
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@ -60,11 +63,12 @@ to create a volume.
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vieux/sshfs
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```
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The plugin requests 2 privileges, the `CAP_SYS_ADMIN` capability to be able
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to do mount inside the plugin and `host networking`.
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The plugin requests 2 privileges:
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- It needs access to the `host` network.
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- It needs the `CAP_SYS_ADMIN` capability, which allows the plugin to run
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the `mount` command.
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2. Check for a value of `true` the `ENABLED` column to verify the plugin
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started without error.
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2. Check that the plugin is enabled in the output of `docker plugin ls`.
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```bash
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$ docker plugin ls
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@ -74,6 +78,8 @@ started without error.
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```
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3. Create a volume using the plugin.
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This example mounts the `/remote` directory on host `1.2.3.4` into a
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volume named `sshvolume`. This volume can now be mounted into containers.
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```bash
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$ docker volume create \
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@ -83,8 +89,16 @@ started without error.
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sshvolume
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```
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4. Verify that the volume was created successfully.
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4. Use the volume `sshvolume`.
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```bash
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$ docker volume ls
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DRIVER NAME
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vieux/sshfs sshvolume
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```
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5. Start a container that uses the volume `sshvolume`.
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```bash
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$ docker run -v sshvolume:/data busybox ls /data
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@ -92,30 +106,22 @@ started without error.
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<content of /remote on machine 1.2.3.4>
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```
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5. Verify the plugin successfully created the volume.
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To disable a plugin, use the `docker plugin disable` command. To completely
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remove it, use the `docker plugin remove` command. For other available
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commands and options, see the
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[command line reference](../reference/commandline/index.md).
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```bash
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$ docker volume ls
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## Developing a plugin
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DRIVER VOLUME NAME
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vieux/sshfs sshvolume
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```
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Currently, there are no CLI commands available to help you develop a plugin.
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This is expected to change in a future release. The manual process for creating
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plugins is described in this section.
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You can stop a plugin with the `docker plugin disable`
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command or remove a plugin with `docker plugin remove`.
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### Plugin location and files
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See the [command line reference](../reference/commandline/index.md) for more
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information.
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## How to develop a plugin
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Plugin creation is currently a manual process. We plan to add automation in a
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future release with a command such as `docker plugin build`.
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This section describes the format of an existing enabled plugin. You have to
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create and format the plugin files by hand.
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Plugins are stored in `/var/lib/docker/plugins`. For instance:
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Plugins are stored in `/var/lib/docker/plugins`. The `plugins.json` file lists
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each plugin's configuration, and each plugin is stored in a directory with a
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unique identifier.
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```bash
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# ls -la /var/lib/docker/plugins
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@ -126,9 +132,12 @@ drwxr-xr-x 3 root root 4096 Aug 8 17:56 cd851ce43a403
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-rw------- 1 root root 2107 Aug 8 18:03 plugins.json
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```
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`plugins.json` is an inventory of all installed plugins. For example:
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### Format of plugins.json
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```bash
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The `plugins.json` is an inventory of all installed plugins. This example shows
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a `plugins.json` with a single plugin installed.
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```json
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# cat plugins.json
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{
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"cd851ce43a403": {
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@ -179,7 +188,10 @@ drwxr-xr-x 3 root root 4096 Aug 8 17:56 cd851ce43a403
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}
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```
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Each folder represents a plugin. For example:
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### Contents of a plugin directory
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Each directory within `/var/lib/docker/plugins/` contains a `rootfs` directory
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and two JSON files.
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```bash
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# ls -la /var/lib/docker/plugins/cd851ce43a403
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@ -189,28 +201,34 @@ drwx------ 19 root root 4096 Aug 8 17:56 rootfs
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-rw------- 1 root root 347 Aug 8 17:56 manifest.json
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```
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`rootfs` represents the root filesystem of the plugin. In this example, it was
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created from a Dockerfile as follows:
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#### The rootfs directory
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The `rootfs` directory represents the root filesystem of the plugin. In this
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example, it was created from a Dockerfile:
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>**Note:** `/run/docker/plugins` is mandatory for docker to communicate with
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the plugin._
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>**Note:** The `/run/docker/plugins` directory is mandatory for docker to communicate with
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the plugin.
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```bash
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$ git clone https://github.com/vieux/docker-volume-sshfs
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$ cd docker-volume-sshfs
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$ docker build -t rootfs .
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$ id=$(docker create rootfs true) # id was cd851ce43a403 when the image was created
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$ mkdir -p /var/lib/docker/plugins/$id/rootfs
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$ docker export "$id" | tar -x -C /var/lib/docker/plugins/$id/rootfs
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$ sudo mkdir -p /var/lib/docker/plugins/$id/rootfs
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$ sudo docker export "$id" | sudo tar -x -C /var/lib/docker/plugins/$id/rootfs
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$ sudo chgrp -R docker /var/lib/docker/plugins/
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$ docker rm -vf "$id"
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$ docker rmi rootfs
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```
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`manifest.json` describes the plugin and `plugin-config.json` contains some
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runtime parameters. [See the Plugins Manifest reference](manifest.md). For example:
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#### The manifest.json and plugin-config.json files
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```bash
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# cat manifest.json
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The `manifest.json` file describes the plugin. The `plugin-config.json` file
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contains runtime parameters and is only required if your plugin has runtime
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parameters. [See the Plugins Manifest reference](manifest.md).
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Consider the following `manifest.json` file.
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```json
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{
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"manifestVersion": "v0",
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"description": "sshFS plugin for Docker",
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@ -227,13 +245,15 @@ runtime parameters. [See the Plugins Manifest reference](manifest.md). For examp
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}
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```
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In this example, you can see the plugin is a volume driver, requires the
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`CAP_SYS_ADMIN` capability, `host networking`, `/go/bin/docker-volume-sshfs` as
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entrypoint and is going to use `/run/docker/plugins/sshfs.sock` to communicate
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with the Docker Engine.
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This plugin is a volume driver. It requires a `host` network and the
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`CAP_SYS_ADMIN` capability. It depends upon the `/go/bin/docker-volume-sshfs`
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entrypoint and uses the `/run/docker/plugins/sshfs.sock` socket to communicate
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with Docker Engine.
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```bash
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# cat plugin-config.json
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Consider the following `plugin-config.json` file.
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```json
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{
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"Devices": null,
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"Args": null,
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@ -242,26 +262,42 @@ with the Docker Engine.
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}
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```
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This plugin doesn't require runtime parameters.
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This plugin has no runtime parameters.
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Both `manifest.json` and `plugin-config.json` are part of the `plugins.json`.
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`manifest.json` is read-only and `plugin-config.json` is read-write.
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Each of these JSON files is included as part of `plugins.json`, as you can see
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by looking back at the example above. After a plugin is installed, `manifest.json`
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is read-only, but `plugin-config.json` is read-write, and includes all runtime
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configuration options for the plugin.
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To summarize, follow the steps below to create a plugin:
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### Creating the plugin
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0. Choose a name for the plugin. Plugin name uses the same format as images,
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for example: `<repo_name>/<name>`.
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1. Create a rootfs in `/var/lib/docker/plugins/$id/rootfs`.
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2. Create manifest.json file in `/var/lib/docker/plugins/$id/`.
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3. Create a `plugin-config.json` if needed.
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4. Create or add a section to `/var/lib/docker/plugins/plugins.json`. Use
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Follow these steps to create a plugin:
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1. Choose a name for the plugin. Plugin name uses the same format as images,
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for example: `<repo_name>/<name>`.
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2. Create a `rootfs` and export it to `/var/lib/docker/plugins/$id/rootfs`
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using `docker export`. See [The rootfs directory](#the-rootfs-directory) for
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an example of creating a `rootfs`.
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3. Create a `manifest.json` file in `/var/lib/docker/plugins/$id/`.
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4. Create a `plugin-config.json` file if needed.
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5. Create or add a section to `/var/lib/docker/plugins/plugins.json`. Use
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`<user>/<name>` as “Name” and `$id` as “Id”.
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5. Restart the Docker Engine.
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6. Run `docker plugin ls`.
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* If your plugin is listed as `ENABLED=true`, you can push it to the
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registry.
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* If the plugin is not listed or if `ENABLED=false`, something went wrong.
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Check the daemon logs for errors.
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7. If you are not already logged in, use `docker login` to authenticate against
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a registry.
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8. Run `docker plugin push <repo_name>/<name>` to push the plugin.
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6. Restart the Docker Engine service.
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7. Run `docker plugin ls`.
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* If your plugin is enabled, you can push it to the
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registry.
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* If the plugin is not listed or is disabled, something went wrong.
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Check the daemon logs for errors.
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8. If you are not already logged in, use `docker login` to authenticate against
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the registry so that you can push to it.
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9. Run `docker plugin push <repo_name>/<name>` to push the plugin.
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The plugin can now be used by any user with access to your registry.
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