Want to hack on Swarm? Awesome! Here are instructions to get you started.

Swarm is a part of the Docker project, and follows the same rules and principles. If you're already familiar with the way Docker does things, you'll feel right at home.

Otherwise, go read Docker's contributions guidelines, issue triaging, review process and branches and tags.

Swarm is written in the Go programming language and manages its dependencies using Godep. Go and Godep also use git to fetch dependencies. So, you are required to install the Go compiler, and the git client (e.g. apt-get install golang git on Ubuntu).

You may need to setup your path and set the $GOPATH and $GOBIN variables, e.g:

mkdir -p ~/projects/swarm
cd ~/projects/swarm
export GOPATH=$PWD
export GOBIN=$GOPATH/bin

As previously mentioned, you need godep to manage dependencies for Swarm. The godep command can be installed using the following command:

go get github.com/tools/godep

and you will find the godep binary under $GOBIN.

Then you can fetch swarm code to your $GOPATH.

go get -d github.com/docker/swarm

First, prepare dependencies for swarm and try to compile it.

cd src/github.com/docker/swarm
$GOBIN/godep restore
go test -v -race ./...
go install

To make sure other will not miss dependencies you've added to Swarm, you'll need to call godep save to make changes to the config file, Godep/Godeps.json. An important thing is that godep will replace the config file by the dependency information it learnt from your local machine. This step will mess the upstream config. So, changes to Godep/Godeps.json must be performed with care.

$GOBIN/godep save ./...
$GOBIN/godep update <an updated package>
git diff # check what added or removed in Godep/Godeps.json
         # then manually add missing dependencies

To make sure you newly added codes will make the build process happy, you can try building Swarm in the same way as defined in Dockerfile.

$GOBIN/godep go install

Then you should find the swarm binary under the $GOBIN directory.

Happy hacking!