Docker Release Process

This document describes how the Docker project is released. The Docker project release process targets the Engine, Compose, Kitematic, Machine, Swarm, Distribution, Notary and their underlying dependencies (libnetwork, libkv, etc...).

Step-by-step technical details of the process are described in

Release cycle

The Docker project follows a time-based release cycle and ships every nine weeks. A release cycle starts the same day the previous release cycle ends.

The first six weeks of the cycle are dedicated to development and review. During this phase, new features and bugfixes submitted to any of the projects are eligible to be shipped as part of the next release. No changeset submitted during this period is however guaranteed to be merged for the current release cycle.

The freeze period

Six weeks after the beginning of the cycle, the codebase is officially frozen and the codebase reaches a state close to the final release. A Release Candidate (RC) gets created at the same time. The freeze period is used to find bugs and get feedback on the state of the RC before the release.

During this freeze period, while the master branch will continue its normal development cycle, no new features are accepted into the RC. As bugs are fixed in master the release owner will selectively ‘cherry-pick’ critical ones to be included into the RC. As the RC changes, new ones are made available for the community to test and review.

This period lasts for three weeks.

How to maximize chances of being merged before the freeze date?

First of all, there is never a guarantee that a specific changeset is going to be merged. However there are different actions to follow to maximize the chances for a changeset to be merged:

  • The team gives priority to review the PRs aligned with the Roadmap (usually defined by a file at the root of the repository).
  • The earlier a PR is opened, the more time the maintainers have to review. For example, if a PR is opened the day before the freeze date, it’s very unlikely that it will be merged for the release.
  • Constant communication with the maintainers (mailing-list, IRC, Github issues, etc.) allows to get early feedback on the design before getting into the implementation, which usually reduces the time needed to discuss a changeset.
  • If the code is commented, fully tested and by extension follows every single rules defined by the CONTRIBUTING guide, this will help the maintainers by speeding up the review.

The release

At the end of the freeze (nine weeks after the start of the cycle), all the projects are released together.

                                        Codebase              Release
Start of                                is frozen             (end of the
the Cycle                               (7th week)            9th week)
|                                       |                     |
|           Development phase           |    Freeze phase     |
|                                       |                     |
                   6 weeks                      3 weeks


If a critical issue is found at the end of the freeze period and more time is needed to address it, the release will be pushed back. When a release gets pushed back, the next release cycle gets delayed as well.