--- description: Develop and use a plugin with the managed plugin system keywords: "API, Usage, plugins, documentation, developer" --- # Docker Engine managed plugin system * [Installing and using a plugin](index.md#installing-and-using-a-plugin) * [Developing a plugin](index.md#developing-a-plugin) * [Debugging plugins](index.md#debugging-plugins) Docker Engine's plugin system allows you to install, start, stop, and remove plugins using Docker Engine. For information about the legacy plugin system available in Docker Engine 1.12 and earlier, see [Understand legacy Docker Engine plugins](legacy_plugins.md). > **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. > **Note**: This example is intended for instructional purposes only. Once the volume is created, your SSH password to the remote host will be exposed as plaintext when inspecting the volume. You should delete the volume as soon as you are done with the example. 1. Install the `sshfs` plugin. ```bash $ 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`. ```bash $ 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. ```bash $ docker volume create \ -d vieux/sshfs \ --name sshvolume \ -o sshcmd=user@1.2.3.4:/remote \ -o password=$(cat file_containing_password_for_remote_host) sshvolume ``` 4. Verify that the volume was created successfully. ```bash $ docker volume ls DRIVER NAME vieux/sshfs sshvolume ``` 5. Start a container that uses the volume `sshvolume`. ```bash $ docker run --rm -v sshvolume:/data busybox ls /data ``` 6. Remove the volume `sshvolume` ```bash docker volume rm sshvolume sshvolume ``` 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](../reference/commandline/index.md). ## 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. ```bash $ 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](config.md). Consider the following `config.json` file. ```json { "description": "sshFS plugin for Docker", "documentation": "https://docs.docker.com/engine/extend/plugins/", "entrypoint": ["/docker-volume-sshfs"], "network": { "type": "host" }, "interface" : { "types": ["docker.volumedriver/1.0"], "socket": "sshfs.sock" }, "linux": { "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 `/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 ./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 `` will show up in `docker plugin ls`. Plugins can be pushed to remote registries with `docker plugin push `. ## Debugging plugins Stdout of a plugin is redirected to dockerd logs. Such entries have a `plugin=` suffix. Here are a few examples of commands for pluginID `f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62` and their corresponding log entries in the docker daemon logs. ```bash $ docker plugin install tiborvass/sample-volume-plugin INFO[0036] Starting... Found 0 volumes on startup plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 ``` ```bash $ docker volume create -d tiborvass/sample-volume-plugin samplevol INFO[0193] Create Called... Ensuring directory /data/samplevol exists on host... plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 INFO[0193] open /var/lib/docker/plugin-data/local-persist.json: no such file or directory plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 INFO[0193] Created volume samplevol with mountpoint /data/samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 INFO[0193] Path Called... Returned path /data/samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 ``` ```bash $ docker run -v samplevol:/tmp busybox sh INFO[0421] Get Called... Found samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 INFO[0421] Mount Called... Mounted samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 INFO[0421] Path Called... Returned path /data/samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 INFO[0421] Unmount Called... Unmounted samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 ``` #### Using docker-runc to obtain logfiles and shell into the plugin. `docker-runc`, the default docker container runtime can be used for debugging plugins. This is specifically useful to collect plugin logs if they are redirected to a file. ```bash $ docker-runc list ID PID STATUS BUNDLE CREATED f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 2679 running /run/docker/libcontainerd/f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 2017-02-06T21:53:03.031537592Z r ``` ```bash $ docker-runc exec f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 cat /var/log/plugin.log ``` If the plugin has a built-in shell, then exec into the plugin can be done as follows: ```bash $ docker-runc exec -t f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62 sh ``` #### Using curl to debug plugin socket issues. To verify if the plugin API socket that the docker daemon communicates with is responsive, use curl. In this example, we will make API calls from the docker host to volume and network plugins using curl 7.47.0 to ensure that the plugin is listening on the said socket. For a well functioning plugin, these basic requests should work. Note that plugin sockets are available on the host under `/var/run/docker/plugins/` ```bash curl -H "Content-Type: application/json" -XPOST -d '{}' --unix-socket /var/run/docker/plugins/e8a37ba56fc879c991f7d7921901723c64df6b42b87e6a0b055771ecf8477a6d/plugin.sock http:/VolumeDriver.List {"Mountpoint":"","Err":"","Volumes":[{"Name":"myvol1","Mountpoint":"/data/myvol1"},{"Name":"myvol2","Mountpoint":"/data/myvol2"}],"Volume":null} ``` ```bash curl -H "Content-Type: application/json" -XPOST -d '{}' --unix-socket /var/run/docker/plugins/45e00a7ce6185d6e365904c8bcf62eb724b1fe307e0d4e7ecc9f6c1eb7bcdb70/plugin.sock http:/NetworkDriver.GetCapabilities {"Scope":"local"} ``` When using curl 7.5 and above, the URL should be of the form `http://hostname/APICall`, where `hostname` is the valid hostname where the plugin is installed and `APICall` is the call to the plugin API. For example, `http://localhost/VolumeDriver.List`