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Manuka: A Docker GraphDriver Development Toolkit

Overview

The toolkit serves as a base environment for Docker graphdriver plugin development, since this feature is still experimental and the guidance for developing the plugin is lacking. The toolkit runs the standard overlay2 graph driver pulled from the Moby code base as a Docker graphdriver plugin and renames it as Manuka.

Pre-requisites

The pre-requisites are listed below but the requirments are not tight.

  • Linux amd64 (preferably Ubuntu 18.04)
  • Docker 18.09 (The plugin interface has changed a little bit since 18)
  • Go 1.12 (> 1.10 and < 1.19)

A Vagrant environment is provided here for quickstart, which pre-installs all the pre-requisites in the VM. To launch the environment, make sure you have VirtualBox and Vagrant properly installed on your machine:

$ cd vagrant && vagrant up && vagrant ssh

If everything works as expected, you should log into a Ubuntu 18.04 VM running locally on your machine via SSH. To clean up the environment,

$ vagrant destroy

If you want to initialize the dev environment on a Linux box, simply runs the build.sh script on the box (assuming it runs Ubuntu 18.04).

Go environment setup

First of all, the environmental variable $GOPATH needs to set properly, default to ${HOME}/go. Go requires all the go code developed under $GOPATH, so the toolkit needs to be placed under $GOPATH. A workaround to avoid diving deep into the $GOPATH is to create a soft link of the code base elsewhere. To fetch the toolkit into $GOPATH.

$ go get github.com/dcvan24/manuka

Build and run the plugin

The toolkit runs the plugin in compliance with the Docker Plugin API v1, in which the plugin is discovered by the daemon as a process listening on a UNIX sokcet located under /var/run/docker/plugins. With Docker Plugin API v2 wherein the plugin is containerized, the MergedDir created in the plugin cannot be reflected on the host, causing errors when containers being started. The problem is suspected related to the misconfiguration of the mountpoint in the plugin but not yet addressed.

To build the plugin, compile the plugin into a binary using go

$ go build main.go && ls 
Dockerfile  README.md  main  main.go  overlay2  vagrant

After the build, you will see the main file as an executable. Execute main using sudo to start the graphdriver plugin

$ sudo ./main

You will see the UNIX socket the graphdriver is listening on under /var/run/docker/plugins

$ sudo ls /var/run/docker/plugins
manuka.sock  runtime-root

Then launch the Docker daemon and let it use the graphdriver plugin. Note that the daemon is able to discover the plugin automatically under /var/run/docker/plugins. To refer to the plugin, simply use the name of the socket, i.e. manuka in this case. Since the feature is still experimental, you need to specify --experimental to turn on the experimental mode of the Docker daemon in order to apply the graphdriver plugin.

$ dockerd -D --experimental -s manuka

Alternatively, you can specify the options in /etc/docker/daemon.json and start the daemon using SystemD (if the Docker daemon is managed in SystemD).

$ cat | sudo tee /etc/docker/daemon.json <<-EOF
{
    "experimental": true,
    "storage-driver": "manuka"
}
EOF
$ sudo systemtcl restart docker