@@ -16,67 +16,86 @@ keywords: "Examples, Usage, volume, docker, data, volumes, plugin, api"

 # Write a volume plugin

 Docker Engine volume plugins enable Engine deployments to be integrated with

-external storage systems, such as Amazon EBS, and enable data volumes to persist

-beyond the lifetime of a single Engine host. See the

+external storage systems such as Amazon EBS, and enable data volumes to persist

+beyond the lifetime of a single Docker host. See the

 [plugin documentation](legacy_plugins.md) for more information.

 ## Changelog

 ### 1.13.0

-- If used as part of the v2 plugin architecture, mountpoints that are part of paths returned by plugin have to be mounted under the directory specified by PropagatedMount in the plugin configuration [#26398](https://github.com/docker/docker/pull/26398)

+- If used as part of the v2 plugin architecture, mountpoints that are part of

+  paths returned by the plugin must be mounted under the directory specified by

+  `PropagatedMount` in the plugin configuration

+  ([#26398](https://github.com/docker/docker/pull/26398))

 ### 1.12.0

-- Add `Status` field to `VolumeDriver.Get` response ([#21006](https://github.com/docker/docker/pull/21006#))

-- Add `VolumeDriver.Capabilities` to get capabilities of the volume driver([#22077](https://github.com/docker/docker/pull/22077))

+- Add `Status` field to `VolumeDriver.Get` response

+  ([#21006](https://github.com/docker/docker/pull/21006#))

+- Add `VolumeDriver.Capabilities` to get capabilities of the volume driver

+  ([#22077](https://github.com/docker/docker/pull/22077))

 ### 1.10.0

-- Add `VolumeDriver.Get` which gets the details about the volume ([#16534](https://github.com/docker/docker/pull/16534))

-- Add `VolumeDriver.List` which lists all volumes owned by the driver ([#16534](https://github.com/docker/docker/pull/16534))

+- Add `VolumeDriver.Get` which gets the details about the volume

+  ([#16534](https://github.com/docker/docker/pull/16534))

+- Add `VolumeDriver.List` which lists all volumes owned by the driver

+  ([#16534](https://github.com/docker/docker/pull/16534))

 ### 1.8.0

-- Initial support for volume driver plugins ([#14659](https://github.com/docker/docker/pull/14659))

+- Initial support for volume driver plugins

+  ([#14659](https://github.com/docker/docker/pull/14659))

 ## Command-line changes

-A volume plugin makes use of the `-v`and `--volume-driver` flag on the `docker run` command.  The `-v` flag accepts a volume name and the `--volume-driver` flag a driver type, for example:

+To give a container access to a volume, use the `--volume` and `--volume-driver`

+flags on the `docker container run` command.  The `--volume` (or `-v`) flag

+accepts a volume name and path on the host, and the `--volume-driver` flag

+accepts a driver type.

-    $ docker run -ti -v volumename:/data --volume-driver=flocker   busybox sh

+```bash

+$ docker volume create --driver=flocker volumename

-This command passes the `volumename` through to the volume plugin as a

-user-given name for the volume. The `volumename` must not begin with a `/`.

+$ docker container run -it --volume volumename:/data busybox sh

+```

+

+### `--volume`

-By having the user specify a  `volumename`, a plugin can associate the volume

-with an external volume beyond the lifetime of a single container or container

-host. This can be used, for example, to move a stateful container from one

-server to another.

+The `--volume` (or `-v`) flag takes a value that is in the format

+`<volume_name>:<mountpoint>`. The two parts of the value are

+separated by a colon (`:`) character.

-By specifying a `volumedriver` in conjunction with a `volumename`, users can use plugins such as [Flocker](https://clusterhq.com/docker-plugin/) to manage volumes external to a single host, such as those on EBS.

+- The volume name is a human-readable name for the volume, and cannot begin with

+  a `/` character. It is referred to as `volume_name` in the rest of this topic.

+- The `Mountpoint` is the path on the host (v1) or in the plugin (v2) where the

+  volume has been made available.

+### `volumedriver`

+

+Specifying a `volumedriver` in conjunction with a `volumename` allows you to

+use plugins such as [Flocker](https://github.com/ScatterHQ/flocker) to manage

+volumes external to a single host, such as those on EBS.

 ## Create a VolumeDriver

 The container creation endpoint (`/containers/create`) accepts a `VolumeDriver`

-field of type `string` allowing to specify the name of the driver. It's default

-value of `"local"` (the default driver for local volumes).

+field of type `string` allowing to specify the name of the driver. If not

+specified, it defaults to `"local"` (the default driver for local volumes).

 ## Volume plugin protocol

-If a plugin registers itself as a `VolumeDriver` when activated, then it is

-expected to provide writeable paths on the host filesystem for the Docker

-daemon to provide to containers to consume.

-

-The Docker daemon handles bind-mounting the provided paths into user

-containers.

+If a plugin registers itself as a `VolumeDriver` when activated, it must

+provide the Docker Daemon with writeable paths on the host filesystem. The Docker

+daemon provides these paths to containers to consume. The Docker daemon makes

+the volumes available by bind-mounting the provided paths into the containers.

 > **Note**: Volume plugins should *not* write data to the `/var/lib/docker/`

 > directory, including `/var/lib/docker/volumes`. The `/var/lib/docker/`

 > directory is reserved for Docker.

-### /VolumeDriver.Create

+### `/VolumeDriver.Create`

 **Request**:

 ```json

@@ -87,9 +106,9 @@ containers.

 ```

 Instruct the plugin that the user wants to create a volume, given a user

-specified volume name.  The plugin does not need to actually manifest the

-volume on the filesystem yet (until Mount is called).

-Opts is a map of driver specific options passed through from the user request.

+specified volume name. The plugin does not need to actually manifest the

+volume on the filesystem yet (until `Mount` is called).

+`Opts` is a map of driver specific options passed through from the user request.

 **Response**:

 ```json

@@ -100,7 +119,7 @@ Opts is a map of driver specific options passed through from the user request.

 Respond with a string error if an error occurred.

-### /VolumeDriver.Remove

+### `/VolumeDriver.Remove`

 **Request**:

 ```json

@@ -109,7 +128,8 @@ Respond with a string error if an error occurred.

 }

 ```

-Delete the specified volume from disk. This request is issued when a user invokes `docker rm -v` to remove volumes associated with a container.

+Delete the specified volume from disk. This request is issued when a user

+invokes `docker rm -v` to remove volumes associated with a container.

 **Response**:

 ```json

@@ -120,7 +140,7 @@ Delete the specified volume from disk. This request is issued when a user invoke

 Respond with a string error if an error occurred.

-### /VolumeDriver.Mount

+### `/VolumeDriver.Mount`

 **Request**:

 ```json

@@ -131,47 +151,76 @@ Respond with a string error if an error occurred.

 ```

 Docker requires the plugin to provide a volume, given a user specified volume

-name. This is called once per container start. If the same volume_name is requested

+name. `Mount` is called once per container start. If the same `volume_name` is requested

 more than once, the plugin may need to keep track of each new mount request and provision

 at the first mount request and deprovision at the last corresponding unmount request.

 `ID` is a unique ID for the caller that is requesting the mount.

 **Response**:

-```json

-{

-    "Mountpoint": "/path/to/directory/on/host",

-    "Err": ""

-}

-```

-Respond with the path on the host filesystem where the volume has been made

-available, and/or a string error if an error occurred.

+- **v1**:

+

+  ```json

+  {

+      "Mountpoint": "/path/to/directory/on/host",

+      "Err": ""

+  }

+  ```

+

+- **v2**:

+

+  ```json

+  {

+      "Mountpoint": "/path/under/PropagatedMount",

+      "Err": ""

+  }

+  ```

+

+`Mountpoint` is the path on the host (v1) or in the plugin (v2) where the volume

+has been made available.

-### /VolumeDriver.Path

+`Err` is either empty or contains an error string.

+

+### `/VolumeDriver.Path`

 **Request**:

+

 ```json

 {

     "Name": "volume_name"

 }

 ```

-Docker needs reminding of the path to the volume on the host.

+Request the path to the volume with the given `volume_name`.

 **Response**:

-```json

-{

-    "Mountpoint": "/path/to/directory/on/host",

-    "Err": ""

-}

-```

-Respond with the path on the host filesystem where the volume has been made

-available, and/or a string error if an error occurred. `Mountpoint` is optional,

-however, the plugin may be queried again later if one is not provided.

+- **v1**:

+

+  ```json

+  {

+      "Mountpoin": "/path/to/directory/on/host",

+      "Err": ""

+  }

+  ```

+

+- **v2**:

+

+  ```json

+  {

+      "Mountpoint": "/path/under/PropagatedMount",

+      "Err": ""

+  }

+  ```

+

+Respond with the path on the host (v1) or inside the plugin (v2) where the

+volume has been made available, and/or a string error if an error occurred.

+

+`Mountpoint` is optional. However, the plugin may be queried again later if one

+is not provided.

-### /VolumeDriver.Unmount

+### `/VolumeDriver.Unmount`

 **Request**:

 ```json

@@ -181,8 +230,8 @@ however, the plugin may be queried again later if one is not provided.

 }

 ```

-Indication that Docker no longer is using the named volume. This is called once

-per container stop.  Plugin may deduce that it is safe to deprovision it at

+Docker is no longer using the named volume. `Unmount` is called once per

+container stop. Plugin may deduce that it is safe to deprovision the volume at

 this point.

 `ID` is a unique ID for the caller that is requesting the mount.

@@ -197,7 +246,7 @@ this point.

 Respond with a string error if an error occurred.

-### /VolumeDriver.Get

+### `/VolumeDriver.Get`

 **Request**:

 ```json

@@ -206,20 +255,36 @@ Respond with a string error if an error occurred.

 }

 ```

-Get the volume info.

+Get info about `volume_name`.

 **Response**:

-```json

-{

-  "Volume": {

-    "Name": "volume_name",

-    "Mountpoint": "/path/to/directory/on/host",

-    "Status": {}

-  },

-  "Err": ""

-}

-```

+

+- **v1**:

+

+  ```json

+  {

+    "Volume": {

+      "Name": "volume_name",

+      "Mountpoint": "/path/to/directory/on/host",

+      "Status": {}

+    },

+    "Err": ""

+  }

+  ```

+

+- **v2**:

+

+  ```json

+  {

+    "Volume": {

+      "Name": "volume_name",

+      "Mountpoint": "/path/under/PropagatedMount",

+      "Status": {}

+    },

+    "Err": ""

+  }

+  ```

 Respond with a string error if an error occurred. `Mountpoint` and `Status` are

 optional.

@@ -235,17 +300,35 @@ optional.

 Get the list of volumes registered with the plugin.

 **Response**:

-```json

-{

-  "Volumes": [

-    {

-      "Name": "volume_name",

-      "Mountpoint": "/path/to/directory/on/host"

-    }

-  ],

-  "Err": ""

-}

-```

+

+- **v1**:

+

+  ```json

+  {

+    "Volumes": [

+      {

+        "Name": "volume_name",

+        "Mountpoint": "/path/to/directory/on/host"

+      }

+    ],

+    "Err": ""

+  }

+  ```

+

+- **v2**:

+

+  ```json

+  {

+    "Volumes": [

+      {

+        "Name": "volume_name",

+        "Mountpoint": "/path/under/PropagatedMount"

+      }

+    ],

+    "Err": ""

+  }

+  ```

+

 Respond with a string error if an error occurred. `Mountpoint` is optional.

@@ -257,8 +340,9 @@ Respond with a string error if an error occurred. `Mountpoint` is optional.

 ```

 Get the list of capabilities the driver supports.

-The driver is not required to implement this endpoint, however, in such cases

-the default values will be taken.

+

+The driver is not required to implement `Capabilities`. If it is not

+implemented, the default values are used.

 **Response**:

 ```json

@@ -270,7 +354,7 @@ the default values will be taken.

 ```

 Supported scopes are `global` and `local`. Any other value in `Scope` will be

-ignored and assumed to be `local`. Scope allows cluster managers to handle the

-volume differently, for instance with a scope of `global`, the cluster manager

-knows it only needs to create the volume once instead of on every engine. More

-capabilities may be added in the future.

+ignored, and `local` is used. `Scope` allows cluster managers to handle the

+volume in different ways. For instance, a scope of `global`, signals to the

+cluster manager that it only needs to create the volume once instead of on each

+Docker host. More capabilities may be added in the future.