What branching strategy should I use during the development/maintenance of a web application?

Question

I am trying to decide on the best branching strategy for a web application project. Here is what I have come up with until now and I would greatly appreciate any comments and experiences.

The way I see it there are two main branching strategies: "branch by release" and "branch by feature".

"Branch by release": Development takes place on the trunk. When the time for a release is near, a branch is made for that release. This branch is then stabilized/tested and finally a release is made. After the release, the branch is merged back into the trunk, while keeping the release branch alive for bug-fixing. Is a bug-fix applied, then it is merged into the trunk ( if the development on the trunk hasn't eclipsed the bug in other means). New features are added to the trunk and don't affect the release branch. When a new release time nears, a new release branch is created a.s.o.

"Branch by feature": The trunk is always the "production" trunk (the code that is live). Bugfixes are commited directly to the trunk. Features for the next release are developed in feature branches.Bugfixes are merged from time-to-time into the feature branches. When release time comes, the features branches are merged into the trunk and the cycle of life continues.

Now the way I see it the big practical difference between these two strategies is that "by release" allows you to maintane different production versions of you software ( when client A has version 1 and client B version 1.5, client is the paying customer in this case). In contrast using the "by feature" strategy you can only support the current production version ( all clients are using latest version).

Since in a typical web application all clients are using the same "latest" version (since they all access the same server), I would assume that the "by feature" approach is the most commonly used. It removes the need to merge "across the hierarchy", say when a bugfix has to be applied to all 3 release versions.

So my current status is that I should go with "branch by feature". If it matters, my team is not very skilled.

Answer 1

If you only have one release live at any time, and you do all development in a single feature branch, then these approaches are effectively the same.

If branch-by-feature to you means having a several branches on the go at once, i'd avoid it like the plague. More branches means more merging, which is a pain in itself, and more integration hell. It's far better to do continuous integration to a single codeline.

If your deployment process is any more involved than branch, test, go live, then an advantage of branch-by-release is that you can have multiple release branches going at once, in different phases: one live and being bugfixed as necessary, and another one being stabilised, tested, going through acceptance, etc, while development continues on the trunk. If you have a live trunk, on the other hand, once you merge a feature branch in with a view to taking it live, you've lost your ability to do bugfixes to the current live system. The feature branch merge becomes a point of no return.

Answer 2

What kind of software are you developing? Shrink wrap? Open Source Project? If so, then go with the "branch by release" or "unstable trunk" approach. Especially if your release cycles are every six months to a year apart.

But if your maintaining a web-based project that has changes going out on shorter frequencies, like once every few weeks or less, then go with the "branch by feature" or "stable trunk" approach. The problem with this approach is integrating multiple feature changes that have sweeping changes make the merge process less than fun. It just really gets difficult.

But both of those work well, but what if you need both? That is, you have a project that deploys says once every couple of weeks with big feature changes, but you find that you have a number of bug fixes that you cannot wait for those feature changes to be ready. Trunk is your release branch with the "branch by feature" approach. What if you could get both releases and features their own branch?

Check out this blog entry by CollabNet's Bob Archer. His Agile Release strategy gives you best of both. I've used this. It's extremely flexible. Even though Bob doesn't show it in his diagram, you can have multiple release branches going at the same time. This means you could have one release branch that is ready for rollout to production, and another that is being prepared for final QA checks. But two things to consider:

First, how good are your developers at merging? You cannot do the the agile release strategy approach by yourself, even if it is a small team. Everyone has to do their part and they really have to understand merging and the tools they are using to do the merge.

Secondly, you are going to need a good grasp on changes that ready and those that are about to be. Release management is key to making this work like clock work. Each feature when ready will need to get assigned to a release branch and merged to it.

Whatever approach you choose, it comes down to what you are developing and the frequency of changes you are releasing for that development.

Answer 3

At the risk of confusing you further: you can have release branches and make all changes on feature branches. These things are not mutually exclusive.

That being said, it sounds like you don't need parallel release families and you want to deploy often, perhaps even continuously. So you would want to have a "stable trunk" that you can release at any time. Feature branches help to keep the trunk stable, because you only merge back to the trunk when the changes are done and have proven themselves.

So I'd say that your choice is a good fit.

Answer 4

These choices are not mutually exclusive - use both. They solve different problems:

"Branch by release" - release branch is used to ensure you can back to the source used to produce the current live version (or previous released versions) while the next version is in development. E.g. This is in order to make changes to the release version for bug fixes or backpatch features from the current development trunk.

"Branch by feature" - used to keep a stable development trunk at all times, which is particularly useful for multiple developers and for experimental "maybe" features.

I would use both, but you can forego one of the approaches if the problem it solves doesn't apply to you or if you have a different solution that problem.

I strongly recommend using a modern DVCS like git or Mercurial. They are geared at parallel development, so they store changes differently than older systems, which makes merging much saner.

Answer 5

I tend to use Git for my projects, but the process I tend to follow goes like this (and should work for Subversion as well):

• for each new feature, create a branch for that feature.
• When everything works, merge it into the staging branch, and deploy it to the staging server (you do have one of those, right?)
• Once we're sure the client is happy with what's on staging, we merge the staging branch into the production branch, tag it as something like production_release_22 or production_release_new_feature_x, and then deploy that tag to the production server.

Tags are never, ever updated - once something gets deployed, it stays that way until more changes are built, tested, and tagged - and then the new tag is deployed. By making sure that it's tags getting deployed and not branches, I keep myself (or others) from doing things like "I'll just commit this one quick change and update the server without testing it".

It's worked pretty well for me so far.