Contributing to Docker

Want to hack on Docker? Awesome! Here are instructions to get you started. They are probably not perfect, please let us know if anything feels wrong or incomplete.

Reporting Issues

When reporting issues on GitHub please include your host OS ( Ubuntu 12.04, Fedora 19, etc... ) and the output of docker version along with the output of docker info if possible.
This information will help us review and fix your issue faster.

Build Environment

For instructions on setting up your development environment, please see our dedicated dev environment setup docs.

Contribution guidelines

Pull requests are always welcome

We are always thrilled to receive pull requests, and do our best to process them as fast as possible. Not sure if that typo is worth a pull request? Do it! We will appreciate it.

If your pull request is not accepted on the first try, don‘t be discouraged! If there’s a problem with the implementation, hopefully you received feedback on what to improve.

We‘re trying very hard to keep Docker lean and focused. We don’t want it to do everything for everybody. This means that we might decide against incorporating a new feature. However, there might be a way to implement that feature on top of docker.

Discuss your design on the mailing list

We recommend discussing your plans on the mailing list before starting to code - especially for more ambitious contributions. This gives other contributors a chance to point you in the right direction, give feedback on your design, and maybe point out if someone else is working on the same thing.

Create issues...

Any significant improvement should be documented as a GitHub issue before anybody starts working on it.

...but check for existing issues first!

Please take a moment to check that an issue doesn't already exist documenting your bug report or improvement proposal. If it does, it never hurts to add a quick “+1” or “I have this problem too”. This will help prioritize the most common problems and requests.


Fork the repo and make changes on your fork in a feature branch:

  • If it's a bugfix branch, name it XXX-something where XXX is the number of the issue
  • If it's a feature branch, create an enhancement issue to announce your intentions, and name it XXX-something where XXX is the number of the issue.

Submit unit tests for your changes. Go has a great test framework built in; use it! Take a look at existing tests for inspiration. Run the full test suite on your branch before submitting a pull request.

Update the documentation when creating or modifying features. Test your documentation changes for clarity, concision, and correctness, as well as a clean documentation build. See docs/ for more information on building the docs and how docs get released.

Write clean code. Universally formatted code promotes ease of writing, reading, and maintenance. Always run go fmt before committing your changes. Most editors have plugins that do this automatically, and there's also a git pre-commit hook:

curl -o .git/hooks/pre-commit && chmod +x .git/hooks/pre-commit

Pull requests descriptions should be as clear as possible and include a reference to all the issues that they address.

Code review comments may be added to your pull request. Discuss, then make the suggested modifications and push additional commits to your feature branch. Be sure to post a comment after pushing. The new commits will show up in the pull request automatically, but the reviewers will not be notified unless you comment.

Before the pull request is merged, make sure that you squash your commits into logical units of work using git rebase -i and git push -f. After every commit the test suite should be passing. Include documentation changes in the same commit so that a revert would remove all traces of the feature or fix.

Commits that fix or close an issue should include a reference like Closes #XXX or Fixes #XXX, which will automatically close the issue when merged.

Add your name to the AUTHORS file, but make sure the list is sorted and your name and email address match your git configuration. The AUTHORS file is regenerated occasionally from the git commit history, so a mismatch may result in your changes being overwritten.

Sign your work

The sign-off is a simple line at the end of the explanation for the patch, which certifies that you wrote it or otherwise have the right to pass it on as an open-source patch. The rules are pretty simple: if you can certify the below:

Docker Developer Grant and Certificate of Origin 1.1

By making a contribution to the Docker Project ("Project"), I represent and
warrant that:

a. The contribution was created in whole or in part by me and I have the right
to submit the contribution on my own behalf or on behalf of a third party who
has authorized me to submit this contribution to the Project; or

b. The contribution is based upon previous work that, to the best of my
knowledge, is covered under an appropriate open source license and I have the
right and authorization to submit that work with modifications, whether
created in whole or in part by me, under the same open source license (unless
I am permitted to submit under a different license) that I have identified in
the contribution; or

c. The contribution was provided directly to me by some other person who
represented and warranted (a) or (b) and I have not modified it.

d. I understand and agree that this Project and the contribution are publicly
known and that a record of the contribution (including all personal
information I submit with it, including my sign-off record) is maintained
indefinitely and may be redistributed consistent with this Project or the open
source license(s) involved.

then you just add a line to every git commit message:

Docker-DCO-1.1-Signed-off-by: Joe Smith <> (github: github_handle)

using your real name (sorry, no pseudonyms or anonymous contributions.)

One way to automate this, is customise your get commit.template by adding a prepare-commit-msg hook to your docker checkout:

curl -o .git/hooks/prepare-commit-msg && chmod +x .git/hooks/prepare-commit-msg
  • Note: the above script expects to find your GitHub user name in git config --get github.user

If you have any questions, please refer to the FAQ in the docs

How can I become a maintainer?

  • Step 1: learn the component inside out
  • Step 2: make yourself useful by contributing code, bugfixes, support etc.
  • Step 3: volunteer on the irc channel (#docker@freenode)
  • Step 4: propose yourself at a scheduled #docker-meeting

Don‘t forget: being a maintainer is a time investment. Make sure you will have time to make yourself available. You don’t have to be a maintainer to make a difference on the project!