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plugins: add example docs for a rexray plugin
Signed-off-by: Tibor Vass <tibor@docker.com>
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Tibor Vass
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---
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description: Volume plugin for Amazon EBS
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keywords: "API, Usage, plugins, documentation, developer, amazon, ebs, rexray, volume"
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title: Volume plugin for Amazon EBS
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---
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<!-- This file is maintained within the docker/docker Github
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# A proof-of-concept Rexray plugin
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In this example, a simple Rexray plugin will be created for the purposes of using
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it on an Amazon EC2 instance with EBS. It is not meant to be a complete Rexray plugin.
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The example source is available at [https://github.com/tiborvass/rexray-plugin](https://github.com/tiborvass/rexray-plugin).
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To learn more about Rexray: [https://github.com/codedellemc/rexray](https://github.com/codedellemc/rexray)
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## 1. Make a Docker image
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The following is the Dockerfile used to containerize rexray.
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```Dockerfile
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FROM debian:jessie
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RUN apt-get update && apt-get install -y --no-install-recommends wget ca-certificates
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RUN wget https://dl.bintray.com/emccode/rexray/stable/0.6.4/rexray-Linux-x86_64-0.6.4.tar.gz -O rexray.tar.gz && tar -xvzf rexray.tar.gz -C /usr/bin && rm rexray.tar.gz
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RUN mkdir -p /run/docker/plugins /var/lib/libstorage/volumes
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ENTRYPOINT ["rexray"]
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CMD ["--help"]
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```
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To build it you can run `image=$(cat Dockerfile | docker build -q -)` and `$image`
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will reference the containerized rexray image.
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## 2. Extract rootfs
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```sh
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$ TMPDIR=/tmp/rexray # for the purpose of this example
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$ # create container without running it, to extract the rootfs from image
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$ docker create --name rexray "$image"
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$ # save the rootfs to a tar archive
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$ docker export -o $TMPDIR/rexray.tar rexray
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$ # extract rootfs from tar archive to a rootfs folder
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$ ( mkdir -p $TMPDIR/rootfs; cd $TMPDIR/rootfs; tar xf ../rexray.tar )
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```
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## 3. Add plugin configuration
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We have to put the following JSON to `$TMPDIR/config.json`:
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```json
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{
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"Args": {
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"Description": "",
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"Name": "",
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"Settable": null,
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"Value": null
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},
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"Description": "A proof-of-concept EBS plugin (using rexray) for Docker",
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"Documentation": "https://github.com/tiborvass/rexray-plugin",
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"Entrypoint": [
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"/usr/bin/rexray", "service", "start", "-f"
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],
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"Env": [
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{
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"Description": "",
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"Name": "REXRAY_SERVICE",
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"Settable": [
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"value"
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],
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"Value": "ebs"
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},
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{
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"Description": "",
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"Name": "EBS_ACCESSKEY",
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"Settable": [
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"value"
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],
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"Value": ""
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},
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{
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"Description": "",
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"Name": "EBS_SECRETKEY",
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"Settable": [
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"value"
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],
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"Value": ""
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}
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],
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"Interface": {
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"Socket": "rexray.sock",
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"Types": [
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"docker.volumedriver/1.0"
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]
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},
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"Linux": {
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"AllowAllDevices": true,
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"Capabilities": ["CAP_SYS_ADMIN"],
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"Devices": null
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},
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"Mounts": [
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{
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"Source": "/dev",
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"Destination": "/dev",
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"Type": "bind",
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"Options": ["rbind"]
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}
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],
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"Network": {
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"Type": "host"
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},
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"PropagatedMount": "/var/lib/libstorage/volumes",
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"User": {},
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"WorkDir": ""
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}
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```
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Please note a couple of points:
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- `PropagatedMount` is needed so that the docker daemon can see mounts done by the
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rexray plugin from within the container, otherwise the docker daemon is not able
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to mount a docker volume.
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- The rexray plugin needs dynamic access to host devices. For that reason, we
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have to give it access to all devices under `/dev` and set `AllowAllDevices` to
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true for proper access.
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- The user of this simple plugin can change only 3 settings: `REXRAY_SERVICE`,
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`EBS_ACCESSKEY` and `EBS_SECRETKEY`. This is because of the reduced scope of this
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plugin. Ideally other rexray parameters could also be set.
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## 4. Create plugin
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`docker plugin create tiborvass/rexray-plugin "$TMPDIR"` will create the plugin.
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```sh
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$ docker plugin ls
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ID NAME DESCRIPTION ENABLED
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2475a4bd0ca5 tiborvass/rexray-plugin:latest A rexray volume plugin for Docker false
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```
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## 5. Test plugin
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```sh
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$ docker plugin set tiborvass/rexray-plugin EBS_ACCESSKEY=$AWS_ACCESSKEY EBS_SECRETKEY=$AWS_SECRETKEY`
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$ docker plugin enable tiborvass/rexray-plugin
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$ docker volume create -d tiborvass/rexray-plugin my-ebs-volume
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$ docker volume ls
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DRIVER VOLUME NAME
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tiborvass/rexray-plugin:latest my-ebs-volume
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$ docker run --rm -v my-ebs-volume:/volume busybox sh -c 'echo bye > /volume/hi'
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$ docker run --rm -v my-ebs-volume:/volume busybox cat /volume/hi
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bye
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```
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## 6. Push plugin
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First, ensure you are logged in with `docker login`. Then you can run:
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`docker plugin push tiborvass/rexray-plugin` to push it like a regular docker
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image to a registry, to make it available for others to install via
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`docker plugin install tiborvass/rexray-plugin EBS_ACCESSKEY=$AWS_ACCESSKEY EBS_SECRETKEY=$AWS_SECRETKEY`.
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@ -154,7 +154,7 @@ This plugin is a volume driver. It requires a `host` network and the
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entrypoint and uses the `/run/docker/plugins/sshfs.sock` socket to communicate
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with Docker Engine. This plugin has no runtime parameters.
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### Creating the plugin
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#### Creating the plugin
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A new plugin can be created by running
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`docker plugin create <plugin-name> ./path/to/plugin/data` where the plugin
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@ -163,4 +163,4 @@ in subdirectory `rootfs`.
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After that the plugin `<plugin-name>` will show up in `docker plugin ls`.
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Plugins can be pushed to remote registries with
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`docker plugin push <plugin-name>`.
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`docker plugin push <plugin-name>`.
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