Main will always be our production branch and it should not be committed to directly. Only branch off for hotfixes, or in rare cases, hard resetting development. The only branches to be merged into Main are release branches, because the only commits that should be made to master are full releases.
The hotfix branches are used to make single commit fixes to development, then open a release branch to PR into Main so we have the ability to roll back. The naming convention for these branches are hotfix/*.
The development branch is the branch we fork feature branches off of, and is used as our staging. Never merge loose features into this branch unless we are 100% certain that the feature is going to production. Hotfixes should be merged here before being merged into Main, or merged into this branch and Main from the same branch so they have the same commit.
Feature branches are for creating new or changing existing features and are to be exclusively forked from development. They will stay in their own branch until we are certain that they are on-track for production/Main. If the feature is on-track for production, we merge it into staging/development to be QA'd and later merged into a release. The naming convention is feat/*
Once staging/development has been sufficiently reviewed, it gets forked into a release branch, which will be used to open a PR to production/Main without tracking future commits from staging/development. The naming convention is release/YYYY.MM.DD or release/YYYY.MM.DD.X if there happens to be multiple releases (usually due to hotfixes) in a single day.
Once merged into production/Main, be sure to tag the Main with the latest release version that has been merged.
At the core, the development model is greatly inspired by existing models out there. The central repo holds two main branches with an infinite lifetime:
- Main
- development
The Main branch at origin should be familiar to every Git user. Parallel to the Main branch, another branch exists called development.
We consider origin/Main to be the main branch where the source code of HEAD always reflects a production-ready state.
We consider origin/development to be the main branch where the source code of HEAD always reflects a state with the latest delivered development changes for the next release. Some would call this the “integration branch”. This is where any automatic nightly builds are built from.
When the source code in the development branch reaches a stable point and is ready to be released, all of the changes should be merged back into Main somehow and then tagged with a release number. How this is done in detail will be discussed further on.
Therefore, each time when changes are merged back into Main, this is a new production release by definition. We tend to be very strict at this, so that theoretically, we could use a Git hook script to automatically build and roll-out our software to our production servers everytime there was a commit on Main.
Next to the main branches Main and development, our development model uses a variety of supporting branches to aid parallel development between team members, ease tracking of features, prepare for production releases and to assist in quickly fixing live production problems. Unlike the main branches, these branches always have a limited life time, since they will be removed eventually.
The different types of branches we may use are:
- Feature branches
- Release branches
- Hotfix branches
Each of these branches have a specific purpose and are bound to strict rules as to which branches may be their originating branch and which branches must be their merge targets. We will walk through them in a minute.
By no means are these branches “special” from a technical perspective. The branch types are categorized by how we use them. They are of course plain old Git branches.
May branch off from: development
Must merge back into: development
Branch naming convention: anything except Main, development, release/YYYY.MM.DD, or hotfix/*
Feature branches (or sometimes called topic branches) are used to develop new features for the upcoming or a distant future release. When starting development of a feature, the target release in which this feature will be incorporated may well be unknown at that point. The essence of a feature branch is that it exists as long as the feature is in development, but will eventually be merged back into develop (to definitely add the new feature to the upcoming release) or discarded (in case of a disappointing experiment).
Feature branches typically exist in developer repos only, not in origin.
When starting work on a new feature, branch off from the development branch.
$ git checkout -b myfeature development
Switched to a new branch "myfeature"Finished features may be merged into the development branch to definitely add them to the upcoming release:
$ git checkout develop
Switched to branch 'develop'
$ git merge --no-ff myfeature
Updating ea1b82a..05e9557
(Summary of changes)
$ git branch -d myfeature
Deleted branch myfeature (was 05e9557).
$ git push origin developThe --no-ff flag causes the merge to always create a new commit object, even if the merge could be performed with a fast-forward. This avoids losing information about the historical existence of a feature branch and groups together all commits that together added the feature. Compare git merge --no-ff and git merge:
In the latter case, it is impossible to see from the Git history which of the commit objects together have implemented a feature—you would have to manually read all the log messages. Reverting a whole feature (i.e. a group of commits), is a true headache in the latter situation, whereas it is easily done if the --no-ff flag was used.
Yes, it will create a few more (empty) commit objects, but the gain is much bigger than the cost.
May branch off from: development
Must merge back into: development and Main
Branch naming convention: release/YYYY.MM.DD
Release branches support preparation of a new production release. They allow for last-minute dotting of i’s and crossing t’s. Furthermore, they allow for minor bug fixes and preparing meta-data for a release (version number, build dates, etc.). By doing all of this work on a release branch, the development branch is cleared to receive features for the next big release.
The key moment to branch off a new release branch from development is when development (almost) reflects the desired state of the new release. At least all features that are targeted for the release-to-be-built must be merged in to development at this point in time. All features targeted at future releases may not—they must wait until after the release branch is branched off.
It is exactly at the start of a release branch that the upcoming release gets assigned a version number—not any earlier. Up until that moment, the development branch reflected changes for the “next release”, but it is unclear whether that “next release” will eventually become 0.3 or 1.0, until the release branch is started. That decision is made on the start of the release branch and is carried out by the project’s rules on version number bumping.
Release branches are created from the development branch. For example, say version 1.1.5 is the current production release and we have a big release coming up. The state of development is ready for the “next release” and we have decided that this will become version 1.2 (rather than 1.1.6 or 2.0). So we branch off and give the release branch a name reflecting the new version number:
$ git checkout -b release-1.2 development
Switched to a new branch "release-1.2"
$ ./bump-version.sh 1.2
Files modified successfully, version bumped to 1.2.
$ git commit -a -m "Bumped version number to 1.2"
[release-1.2 74d9424] Bumped version number to 1.2
1 files changed, 1 insertions(+), 1 deletions(-)After creating a new branch and switching to it, we bump the version number. Here, bump-version.sh is a fictional shell script that changes some files in the working copy to reflect the new version. (This can of course be a manual change—the point being that some files change.) Then, the bumped version number is committed.
This new branch may exist there for a while, until the release may be rolled out definitely. During that time, bug fixes may be applied in this branch (rather than on the development branch). Adding large new features here is strictly prohibited. They must be merged into development, and therefore, wait for the next big release.
When the state of the release branch is ready to become a real release, some actions need to be carried out. First, the release branch is merged into master (since every commit on master is a new release by definition, remember). Next, that commit on master must be tagged for easy future reference to this historical version. Finally, the changes made on the release branch need to be merged back into develop, so that future releases also contain these bug fixes.
The first two steps in Git:
$ git checkout master
Switched to branch 'master'
$ git merge --no-ff release-1.2
Merge made by recursive.
(Summary of changes)
$ git tag -a 1.2The release is now done, and tagged for future reference.
To keep the changes made in the release branch, we need to merge those back into develop, though. In Git:
$ git checkout develop
Switched to branch 'develop'
$ git merge --no-ff release-1.2
Merge made by recursive.
(Summary of changes)This step may well lead to a merge conflict (probably even, since we have changed the version number). If so, fix it and commit.
Do not delete release branches until they are 4-6 major versions behind, in case we need to reset Main and development
May branch off from: Main
Must merge back into: development and Main
Branch naming convention: hotfix/*
Hotfix branches are very much like release branches in that they are also meant to prepare for a new production release, albeit unplanned. They arise from the necessity to act immediately upon an undesired state of a live production version. When a critical bug in a production version must be resolved immediately, a hotfix branch may be branched off from the corresponding tag on the master branch that marks the production version.
The essence is that work of team members (on the develop branch) can continue, while another person is preparing a quick production fix.
Hotfix branches are created from the master branch. For example, say version 1.2 is the current production release running live and causing troubles due to a severe bug. But changes on develop are yet unstable. We may then branch off a hotfix branch and start fixing the problem:
$ git checkout -b hotfix-1.2.1 master
Switched to a new branch "hotfix-1.2.1"
$ ./bump-version.sh 1.2.1
Files modified successfully, version bumped to 1.2.1.
$ git commit -a -m "Bumped version number to 1.2.1"
[hotfix-1.2.1 41e61bb] Bumped version number to 1.2.1
1 files changed, 1 insertions(+), 1 deletions(-)Don’t forget to bump the version number after branching off!
Then, fix the bug and commit the fix in one or more separate commits.
$ git commit -m "Fixed severe production problem"
[hotfix-1.2.1 abbe5d6] Fixed severe production problem
5 files changed, 32 insertions(+), 17 deletions(-)When finished, the bugfix needs to be merged back into master, but also needs to be merged back into develop, in order to safeguard that the bugfix is included in the next release as well. This is completely similar to how release branches are finished.
First, update master and tag the release.
$ git checkout master
Switched to branch 'master'
$ git merge --no-ff hotfix-1.2.1
Merge made by recursive.
(Summary of changes)
$ git tag -a 1.2.1Next, include the bugfix in develop, too:
$ git checkout develop
Switched to branch 'develop'
$ git merge --no-ff hotfix-1.2.1
Merge made by recursive.
(Summary of changes)The one exception to the rule here is that, when a release branch currently exists, the hotfix changes need to be merged into that release branch, instead of develop. Back-merging the bugfix into the release branch will eventually result in the bugfix being merged into develop too, when the release branch is finished. (If work in develop immediately requires this bugfix and cannot wait for the release branch to be finished, you may safely merge the bugfix into develop now already as well.)
Finally, remove the temporary branch:
$ git branch -d hotfix-1.2.1
Deleted branch hotfix-1.2.1 (was abbe5d6).While there is nothing really shocking new to this branching model, the “big picture” figure that this post began with has turned out to be tremendously useful in our projects. It forms an elegant mental model that is easy to comprehend and allows team members to develop a shared understanding of the branching and releasing processes.
A high-quality PDF version of the figure is provided here. Go ahead and hang it on the wall for quick reference at any time.