git分支的管理策略最佳实践
2016-05-11 15:09
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In this post I present the development model that I’ve introduced for some of my projects (both at work and private) about a year ago, and which has turned out to be very successful. I’ve been meaning to write about it for a while now, but I’ve never really
found the time to do so thoroughly, until now. I won’t talk about any of the projects’ details, merely about the branching strategy and release management.
It focuses around Git as the tool for the versioning of all of our source code. (By the way, if you’re interested in Git, our company GitPrime provides
some awesome realtime data analytics on software engineering performance.)
For a thorough discussion on the pros and cons of Git compared to centralized source code control systems, see the web.
There are plenty of flame wars going on there. As a developer, I prefer Git above all other tools around today. Git really changed the way developers think of merging and branching. From the classic CVS/Subversion world I came from, merging/branching has always
been considered a bit scary (“beware of merge conflicts, they bite you!”) and something you only do every once in a while.
But with Git, these actions are extremely cheap and simple, and they are considered one of the core parts of your daily workflow, really. For example, in CVS/Subversion books,
branching and merging is first discussed in the later chapters (for advanced users), while in every Git book,
it’s already covered in chapter 3 (basics).
As a consequence of its simplicity and repetitive nature, branching and merging are no longer something to be afraid of. Version control tools are supposed to assist in branching/merging more than anything else.
Enough about the tools, let’s head onto the development model. The model that I’m going to present here is essentially no more than a set of procedures that every team member has to follow in order to come to a managed software development process.
The repository setup that we use and that works well with this branching model, is that with a central “truth” repo. Note that this repo is only considered to be the central one (since Git is a DVCS, there is no
such thing as a central repo at a technical level). We will refer to this repo as
is familiar to all Git users.
Each developer pulls and pushes to origin. But besides the centralized push-pull relationships, each developer may also pull changes from other peers to form sub teams. For example, this might be useful to work together with two or more developers on a big
new feature, before pushing the work in progress to
of Alice and Bob, Alice and David, and Clair and David.
Technically, this means nothing more than that Alice has defined a Git remote, named
repository, and vice versa.
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:
The
be familiar to every Git user. Parallel to the
We consider
reflects a production-ready state.
We consider
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
changes should be merged back into
in detail will be discussed further on.
Therefore, each time when changes are merged back into
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
Next to the main branches
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:
or
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
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
When starting work on a new feature, branch off from the
Finished features may be merged into the
The
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:
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
Yes, it will create a few more (empty) commit objects, but the gain is much bigger than the cost.
May branch off from:
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
The key moment to branch off a new release branch from
state of the new release. At least all features that are targeted for the release-to-be-built must be merged in to
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
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
release and we have a big release coming up. The state of
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:
After creating a new branch and switching to it, we bump the version number. Here,
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
Adding large new features here is strictly prohibited. They must be merged into
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
every commit on
Next, that commit on
the changes made on the release branch need to be merged back into
contain these bug fixes.
The first two steps in Git:
The release is now done, and tagged for future reference.
Edit: You might as well want to use the
To keep the changes made in the release branch, we need to merge those back into
This step may well lead to a merge conflict (probably even, since we have changed the version number). If so, fix it and commit.
Now we are really done and the release branch may be removed, since we don’t need it anymore:
May branch off from:
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
a quick production fix.
Hotfix branches are created from the
release running live and causing troubles due to a severe bug. But changes on
may then branch off a hotfix branch and start fixing the problem:
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.
Finishing a hotfix branch
When finished, the bugfix needs to be merged back into
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
Edit: You might as well want to use the
Next, include the bugfix in
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
Back-merging the bugfix into the release branch will eventually result in the bugfix being merged into
when the release branch is finished. (If work in
for the release branch to be finished, you may safely merge the bugfix into
Finally, remove the temporary branch:
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.
Update: And for anyone who requested it: here’s the gitflow-model.src.key of
the main diagram image (Apple Keynote).
Git-branching-model.pdf
If you want to get in touch, I'm @nvie on Twitter.
found the time to do so thoroughly, until now. I won’t talk about any of the projects’ details, merely about the branching strategy and release management.
It focuses around Git as the tool for the versioning of all of our source code. (By the way, if you’re interested in Git, our company GitPrime provides
some awesome realtime data analytics on software engineering performance.)
Why git?
For a thorough discussion on the pros and cons of Git compared to centralized source code control systems, see the web.There are plenty of flame wars going on there. As a developer, I prefer Git above all other tools around today. Git really changed the way developers think of merging and branching. From the classic CVS/Subversion world I came from, merging/branching has always
been considered a bit scary (“beware of merge conflicts, they bite you!”) and something you only do every once in a while.
But with Git, these actions are extremely cheap and simple, and they are considered one of the core parts of your daily workflow, really. For example, in CVS/Subversion books,
branching and merging is first discussed in the later chapters (for advanced users), while in every Git book,
it’s already covered in chapter 3 (basics).
As a consequence of its simplicity and repetitive nature, branching and merging are no longer something to be afraid of. Version control tools are supposed to assist in branching/merging more than anything else.
Enough about the tools, let’s head onto the development model. The model that I’m going to present here is essentially no more than a set of procedures that every team member has to follow in order to come to a managed software development process.
Decentralized but centralized
The repository setup that we use and that works well with this branching model, is that with a central “truth” repo. Note that this repo is only considered to be the central one (since Git is a DVCS, there is nosuch thing as a central repo at a technical level). We will refer to this repo as
origin, since this name
is familiar to all Git users.
Each developer pulls and pushes to origin. But besides the centralized push-pull relationships, each developer may also pull changes from other peers to form sub teams. For example, this might be useful to work together with two or more developers on a big
new feature, before pushing the work in progress to
originprematurely. In the figure above, there are subteams
of Alice and Bob, Alice and David, and Clair and David.
Technically, this means nothing more than that Alice has defined a Git remote, named
bob, pointing to Bob’s
repository, and vice versa.
The main branches
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:
master
develop
The
masterbranch at
originshould
be familiar to every Git user. Parallel to the
masterbranch, another branch exists called
develop.
We consider
origin/masterto be the main branch where the source code of
HEADalways
reflects a production-ready state.
We consider
origin/developto be the main branch where the source code of
HEADalways
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
developbranch reaches a stable point and is ready to be released, all of the
changes should be merged back into
mastersomehow 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
master, 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
master.
Supporting branches
Next to the main branches masterand
develop,
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.
Feature branches
May branch off from:
developMust merge back into:
developBranch naming convention:anything except
master,
develop,
release-*,
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.
Creating a feature branch
When starting work on a new feature, branch off from the developbranch.
$ git checkout -b myfeature develop Switched to a new branch "myfeature"
Incorporating a finished feature on develop
Finished features may be merged into the developbranch 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 develop
The
--no-ffflag 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:
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-ffflag was used.
Yes, it will create a few more (empty) commit objects, but the gain is much bigger than the cost.
Release branches
May branch off from:developMust merge back into:
developand
masterBranch naming convention:
release-*
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
developbranch is cleared to receive features for the next big release.
The key moment to branch off a new release branch from
developis when develop (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
developat
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
developbranch
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.
Creating a release branch
Release branches are created from the developbranch. For example, say version 1.1.5 is the current production
release and we have a big release coming up. The state of
developis 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 develop 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.shis 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
developbranch).
Adding large new features here is strictly prohibited. They must be merged into
develop, and therefore,
wait for the next big release.
Finishing a release branch
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
masteris a new release by definition, remember).
Next, that commit on
mastermust 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 1.2
The release is now done, and tagged for future reference.
Edit: You might as well want to use the
-sor
-u <key>flags to sign your tag cryptographically.
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.
Now we are really done and the release branch may be removed, since we don’t need it anymore:
$ git branch -d release-1.2 Deleted branch release-1.2 (was ff452fe).
Hotfix branches
May branch off from:
masterMust merge back into:
developand
masterBranch 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
developbranch) can continue, while another person is preparing
a quick production fix.
Creating the hotfix branch
Hotfix branches are created from the masterbranch. For example, say version 1.2 is the current production
release running live and causing troubles due to a severe bug. But changes on
developare 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(-)
Finishing a hotfix branch
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
masterand 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 1.2.1
Edit: You might as well want to use the
-sor
-u <key>flags to sign your tag cryptographically.
Next, 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
developtoo,
when the release branch is finished. (If work in
developimmediately requires this bugfix and cannot wait
for the release branch to be finished, you may safely merge the bugfix into
developnow already as well.)
Finally, remove the temporary branch:
$ git branch -d hotfix-1.2.1 Deleted branch hotfix-1.2.1 (was abbe5d6).
Summary
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 membersto 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.
Update: And for anyone who requested it: here’s the gitflow-model.src.key of
the main diagram image (Apple Keynote).
Git-branching-model.pdf
If you want to get in touch, I'm @nvie on Twitter.
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