Sun, 09 Oct 2016

Git Flow vs. Continuous Delivery

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I've often read the recommendation to use git flow as a branching model for software development projects, and I've even introduced it at some projects at work.

But when we adopted Continuous Delivery, it became pretty clear that git flow and Continuous Integration and Continuous Delivery don't mix well.

So you develop features and bug fixes in branches, and merge them into the develop branch. This means the develop branch needs to be the focus of your testing efforts, it needs to be automatically deployed to a testing environment and so on.

And then, git flow recommends that for going to production, you build packages from the master branch, and release them. The problem is that by building a new package or binary from the master branch, you invalidate all the testing you did in the develop branch.

Even if the code in the master branch is identical to that in the develop branch, you might get a different binary due to non-reproducible builds, changes in the versions of build tools and compilers, or even cosmic rays or other sources of random bit flips in RAM or on disk. And if you always get an identical binary, why bother to do a second build at all?

The spirit of Continuous Delivery is very much to test the heck out of one build artifact, and if it proves to be of high quality, bring it to production.

An Alternative: Trunk-Based Development

A workflow that fits better with Continuous Delivery is to do most development in the same branch. This branch is automatically tested and deployed to a testing environment, and if all the tests are successful, either deployed to production automatically, or after manual approval.

If there are features that you don't yet want your end users to see, you can hide them behind feature flags. Of course, feature flags come with their own complexity, and should be kept to a minimum.

Keeping your software releasable all the time is a core principle of Continuous Delivery, so if you practise that, and encounter a bug that needs an immediate fix, chances are high that you can apply the fix in the main development branch, and deploy it using the same automation that you use for your usual feature development.

If that doesn't work, you can always pause your deployment pipeline for the regular development branch, create a hotfix branch, and use the regular deployment code, but based on the hotfix branch, and bring your changes to your testing and production environments.

Does That Mean I Should Abandon Git Flow?

My experience is limited to pretty small development teams, and to certain kinds of software. For example, I've never developed software for embedded devices. So I certainly can't talk about all the different modes of operations.

My main point is that git flow doesn't mix well with Continuous Delivery, and that you shouldn't recommend it blindly without understanding the context in which it is used.

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