【版本控制管理】 深入 001 A successful Git branching model GIT 项目分支策略和释放管理

本文，转于老外的一个实际git的管理项目和想法。这篇文章作者把自己工作中实际使用git的版本控制构建做了总结。对的，就是git 的版本管理的构架。文章列举了一个复杂的项目开发生命维护的框架，构建了一个git版本控制的模型。有非常有意义的参考。

原文地址如下：http://nvie.com/posts/a-successful-git-branching-model/

作者：By Vincent
Driessen

GIT 项目分支策略和释放管理

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.)

工具选择 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 可怕的 (“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.

没有中心的中心 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 no
such 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 

origin

 prematurely. 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.

主分支 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 

master

 branch at 

origin

 should
be familiar to every Git user. Parallel to the 

master

 branch, another branch exists called

develop

.

We consider 

origin/master

 to be the main branch where the source code of 

HEAD

 always
reflects a production-ready state.【这是一个重要的概念，主分支应该是一个总是为产品级别READY的状态，中间不应该有任何打断】

We consider 

origin/develop

 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 

develop

 branch reaches a
stable point and is ready to be released, all of the changes should be merged back into 

master

 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 

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

.【master上的每一次merged都必须严格地能让自动编译工具编译成功，并且可以随时溯源】

支持分支 Supporting branches 【必须有有限的生存周期】

Next to the main branches 

master

 and 

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.【最终将被移出】

The different types of branches we may use are:
Feature branches  
功能开发分支
Release branches
代码发布分支
Hotfix branches
紧急修复分支

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.【这些短生命周期的分支，必须严格遵循严格的标准定义 第一，他们是从哪里切出来的分支。
第二，他们将从哪里合并回去。】

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.

新功能实现分支 Feature branches 

May branch off from:

develop

Must merge back into:

develop

Branch 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 

develop

 branch.

$ git checkout -b myfeature develop
Switched to a new branch "myfeature"

Incorporating a finished feature on develop 

Finished features may be merged into the 

develop

 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 develop

The 

--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:【这点非常有意思，为了保证记录必须如此选择】



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.

版本发布分支  Release branches 

May branch off from:

develop

Must merge back into:

develop

 and 

master

Branch 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

develop

 branch is cleared to receive features for the next big release.

The key moment to branch off a new release branch from 

develop

 is 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 

develop

 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 

develop

 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.

Creating a release branch 

Release branches are created from the 

develop

 branch. For example, say version 1.1.5 is the current production
release and we have a big release coming up. The state of 

develop

 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 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.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 

develop

 branch).
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 

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 1.2

The release is now done, and tagged for future reference.

Edit: You might as well want to use the 

-s

 or 

-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:

master

Must merge back into:

develop

 and 

master

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.

Creating the hotfix branch 

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(-)

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 

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 1.2.1

Edit: You might as well want to use the 

-s

 or 

-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 

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).

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 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

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