gitlab_flow.md

Introduction

Version management with git makes branching and merging much easier than older versioning systems such as SVN. This allows a wide variety of branching strategies and workflows. Almost all of these are an improvement over the methods used before git. But many organizations end up with a workflow that is not clearly defined, overly complex or not integrated with issue tracking systems. Therefore we propose the GitLab flow as clearly defined set of best practices. It combines feature driven development and feature branches with issue tracking.

Organizations coming to git from other version control systems frequently find it hard to develop an effective workflow. This article describes the GitLab flow that integrates the git workflow with an issue tracking system. It offers a simple, transparent and effective way to work with git.

When converting to git you have to get used to the fact that there are three steps before a commit is shared with colleagues. Most version control systems have only one step, committing from the working copy to a shared server. In git you add files from the working copy to the staging area. After that you commit them to the local repo. The third step is pushing to a shared remote repository. After getting used to these three steps the branching model becomes the challenge.

Since many organizations new to git have no conventions how to work with it, it can quickly become a mess. The biggest problem they run into is that many long running branches that each contain part of the changes are around. People have a hard time figuring out which branch they should develop on or deploy to production. Frequently the reaction to this problem is to adopt a standardized pattern such as git flow and GitHub flow. We think there is still room for improvement and will detail a set of practices we call GitLab flow.

Git flow and its problems

Git flow was one of the first proposals to use git branches and it has gotten a lot of attention. It advocates a master branch and a separate develop branch as well as supporting branches for features, releases and hotfixes. The development happens on the develop branch, moves to a release branch and is finally merged into the master branch. Git flow is a well defined standard but its complexity introduces two problems. The first problem is that developers must use the develop branch and not master, master is reserved for code that is released to production. It is a convention to call your default branch master and to mostly branch from and merge to this. Since most tools automatically make the master branch the default one and display that one by default it is annoying to have to switch to another one. The second problem of git flow is the complexity introduced by the hotfix and release branches. These branches can be a good idea for some organizations but are overkill for the vast majority of them. Nowadays most organizations practice continuous delivery which means that your default branch can be deployed. This means that hotfix and release branches can be prevented including all the ceremony they introduce. An example of this ceremony is the merging back of release branches. Though specialized tools do exist to solve this, they require documentation and add complexity. Frequently developers make a mistake and for example changes are only merged into master and not into the develop branch. The root cause of these errors is that git flow is too complex for most of the use cases. And doing releases doesn't automatically mean also doing hotfixes.

GitHub flow as a simpler alternative

In reaction to git flow a simpler alternative was detailed, GitHub flow. This flow has only feature branches and a master branch. This is very simple and clean, many organizations have adopted it with great success. Atlassian recommends a similar strategy although they rebase feature branches. Merging everything into the master branch and deploying often means you minimize the amount of code in 'inventory' which is in line with the lean and continuous delivery best practices. But this flow still leaves a lot of questions unanswered regarding deployments, environments, releases and integrations with issues. With GitLab flow we offer additional guidance for these questions.

Production branch with GitLab flow

GitHub flow does assume you are able to deploy to production every time you merge a feature branch. This is possible for SaaS applications but are many cases where this is not possible. One would be a situation where you are not in control of the exact release moment, for example an iOS application that needs to pass App Store validation. Another example is when you have deployment windows (workdays from 10am to 4pm when the operations team is at full capacity) but you also merge code at other times. In these cases you can make a production branch that reflects the deployed code. You can deploy a new version by merging in master to the production branch. If you need to know what code is in production you can just checkout the production branch to see. The approximate time of deployment is easily visible as the merge commit in the version control system. This time is pretty accurate if you automatically deploy your production branch. If you need a more exact time you can have your deployment script create a tag on each deployment. This flow prevents the overhead of releasing, tagging and merging that is common to git flow.

Environment branches with GitLab flow

It might be a good idea to have an environment that is automatically updated to the master branch. Only in this case, the name of this environment might differ from the branch name. Suppose you have a staging environment, a pre-production environment and a production environment. In this case the master branch is deployed on staging. When someone wants to deploy to pre-production they create a merge request from the master branch to the pre-production branch. And going live with code happens by merging the pre-production branch into the production branch. This workflow where commits only flow downstream ensures that everything has been tested on all environments. If you need to cherry-pick a commit with a hotfix it is common to develop it on a feature branch and merge it into master with a merge request, do not delete the feature branch. If master is good to go (it should be if you a practicing continuous delivery) you then merge it to the other branches. If this is not possible because more manual testing is required you can send merge requests from the feature branch to the downstream branches. An 'extreme' version of environment branches are setting up an environment for each feature branch as done by Teatro.

Release branches with GitLab flow

Only in case you need to release software to the outside world you need to work with release branches. In this case, each branch contains a minor version (2-3-stable, 2-4-stable, etc.). The stable branch uses master as a starting point and is created as late as possible. By branching as late as possible you minimize the time you have to apply bug fixes to multiple branches. After a release branch is announced, only serious bug fixes are included in the release branch. If possible these bug fixes are first merged into master and then cherry-picked into the release branch. This way you can't forget to cherry-pick them into master and encounter the same bug on subsequent releases. This is called an 'upstream first' policy that is also practiced by Google and Red Hat. Every time a bug-fix is included in a release branch the patch version is raised (to comply with Semantic Versioning) by setting a new tag. Some projects also have a stable branch that points to the same commit as the latest released branch. In this flow it is not common to have a production branch (or git flow master branch).

Merge/pull requests with GitLab flow

Merge or pull requests are created in a git management application and ask an assigned person to merge two branches. Tools such as GitHub and Bitbucket choose the name pull request since the first manual action would be to pull the feature branch. Tools such as GitLab and Gitorious choose the name merge request since that is the final action that is requested of the assignee. In this article we'll refer to them as merge requests.

If you work on a feature branch for more than a few hours it is good to share the intermediate result with the rest of the team. This can be done by creating a merge request without assigning it to anyone, instead you mention people in the description or a comment (/cc @mark @susan). This means it is not ready to be merged but feedback is welcome. Your team members can comment on the merge request in general or on specific lines with line comments. The merge requests serves as a code review tool and no separate tools such as Gerrit and reviewboard should be needed. If the review reveals shortcomings anyone can commit and push a fix. Commonly the person to do this is the creator of the merge/pull request. The diff in the merge/pull requests automatically updates when new commits are pushed on the branch.

When you feel comfortable with it to be merged you assign it to the person that knows most about the codebase you are changing and mention any other people you would like feedback from. There is room for more feedback and after the assigned person feels comfortable with the result the branch is merged. If the assigned person does not feel comfortable they can close the merge request without merging.

In GitLab it is common to protect the long-lived branches (e.g. the master branch) so that normal developers can't modify these protected branches. So if you want to merge it into a protected branch you assign it to someone with master authorizations.

Issues with GitLab flow