442 lines
26 KiB
Markdown
442 lines
26 KiB
Markdown
---
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stage: Create
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group: Source Code
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
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disqus_identifier: 'https://docs.gitlab.com/ee/workflow/gitlab_flow.html'
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---
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# Introduction to GitLab Flow **(FREE)**
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Git allows a wide variety of branching strategies and workflows.
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Because of this, many organizations end up with workflows that are too complicated, not clearly defined, or not integrated with issue tracking systems.
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Therefore, we propose GitLab flow as a clearly defined set of best practices.
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It combines [feature-driven development](https://en.wikipedia.org/wiki/Feature-driven_development) and [feature branches](https://martinfowler.com/bliki/FeatureBranch.html) with issue tracking.
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Organizations coming to Git from other version control systems frequently find it hard to develop a productive workflow.
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This article describes GitLab flow, which integrates the Git workflow with an issue tracking system.
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It offers a transparent and effective way to work with Git:
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```mermaid
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graph LR
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subgraph Git workflow
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A[Working copy] --> |git add| B[Index]
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B --> |git commit| C[Local repository]
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C --> |git push| D[Remote repository]
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end
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```
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When converting to Git, you have to get used to the fact that it takes three steps to share a commit with colleagues.
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Most version control systems have only one step: committing from the working copy to a shared server.
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In Git, you add files from the working copy to the staging area. After that, you commit them to your local repository.
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The third step is pushing to a shared remote repository.
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After getting used to these three steps, the next challenge is the branching model.
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Because many organizations new to Git have no conventions for how to work with it, their repositories can quickly become messy.
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The biggest problem is that many long-running branches emerge that all contain part of the changes.
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People have a hard time figuring out which branch has the latest code, or which branch to deploy to production.
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Frequently, the reaction to this problem is to adopt a standardized pattern such as [Git flow](https://nvie.com/posts/a-successful-git-branching-model/) and [GitHub flow](http://scottchacon.com/2011/08/31/github-flow.html).
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We think there is still room for improvement. In this document, we describe a set of practices we call GitLab flow.
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For a video introduction of how this works in GitLab, see [GitLab Flow](https://youtu.be/InKNIvky2KE).
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## Git flow and its problems
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<!-- vale gitlab.Spelling = NO -->
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<!-- vale gitlab.Spelling = YES -->
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Git flow was one of the first proposals to use Git branches, and it has received
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a lot of attention. It suggests a `main` branch and a separate `develop` branch,
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with supporting branches for features, releases, and hotfixes. The development
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happens on the `develop` branch, moves to a release branch, and is finally merged
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into the `main` branch.
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Git flow is a well-defined standard, but its complexity introduces two problems.
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The first problem is that developers must use the `develop` branch and not `main`. `main` is reserved for code that is released to production.
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It is a convention to call your default branch `main` and to mostly branch from and merge to this.
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Because most tools automatically use the `main` branch as the default, it is annoying to have to switch to another branch.
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The second problem of Git flow is the complexity introduced by the hotfix and release branches.
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These branches can be a good idea for some organizations but are overkill for the vast majority of them.
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Nowadays, most organizations practice continuous delivery, which means that your default branch can be deployed.
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Continuous delivery removes the need for hotfix and release branches, including all the ceremony they introduce.
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An example of this ceremony is the merging back of release branches.
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Though specialized tools do exist to solve this, they require documentation and add complexity.
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Frequently, developers make mistakes such as merging changes only into `main` and not into the `develop` branch.
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The reason for these errors is that Git flow is too complicated for most use cases.
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For example, many projects do releases but don't need to do hotfixes.
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## GitHub flow as a simpler alternative
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In reaction to Git flow, GitHub created a simpler alternative.
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[GitHub flow](https://docs.github.com/en/get-started/quickstart/github-flow) has only feature branches and a `main` branch:
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```mermaid
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graph TD
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subgraph Feature branches in GitHub Flow
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A[main branch] ===>B[main branch]
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D[nav branch] --> |add navigation| B
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B ===> C[main branch]
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E[feature-branch] --> |add feature| C
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C ==> F[main branch]
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end
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```
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This flow is clean and straightforward, and many organizations have adopted it with great success.
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Atlassian recommends [a similar strategy](https://www.atlassian.com/blog/git/simple-git-workflow-is-simple), although they rebase feature branches.
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Merging everything into the `main` branch and frequently deploying means you minimize the amount of unreleased code. This approach is in line with lean and continuous delivery best practices.
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However, this flow still leaves a lot of questions unanswered regarding deployments, environments, releases, and integrations with issues.
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With GitLab flow, we offer additional guidance for these questions.
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## Production branch with GitLab flow
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GitHub flow assumes you can deploy to production every time you merge a feature branch.
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While this is possible in some cases, such as SaaS applications, there are some cases where this is not possible, such as:
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- You don't control the timing of a release. For example, an iOS application that
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is released when it passes App Store validation.
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- You have deployment windows - for example, workdays from 10 AM to 4 PM when the
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operations team is at full capacity - but you also merge code at other times.
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In these cases, you can make a production branch that reflects the deployed code.
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You can deploy a new version by merging `development` into the production branch:
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```mermaid
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graph TD
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subgraph Production branch in GitLab Flow
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A[development] ==>B[development]
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B ==> C[development]
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C ==> D[development]
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E[production] ====> F[production]
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C --> |deployment| F
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D ==> G[development]
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F ==> H[production]
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end
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```
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If you need to know what code is in production, you can check out the production branch to see.
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The approximate time of deployment is visible as the merge commit in the version control system.
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This time is pretty accurate if you automatically deploy your production branch.
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If you need a more exact time, you can have your deployment script create a tag on each deployment.
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This flow prevents the overhead of releasing, tagging, and merging that happens with Git flow.
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## Environment branches with GitLab flow
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It might be a good idea to have an environment that is automatically updated to the `staging` branch.
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Only, in this case, the name of this environment might differ from the branch name.
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Suppose you have a staging environment, a pre-production environment, and a production environment:
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```mermaid
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graph LR
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subgraph Environment branches in GitLab Flow
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A[staging] ==> B[staging]
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B ==> C[staging]
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C ==> D[staging]
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A --> |deploy to<br>pre-prod| G
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F[pre-prod] ==> G[pre-prod]
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G ==> H[pre-prod]
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H ==> I[pre-prod]
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C --> |deploy to<br>pre-prod| I
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J[production] ==> K[production]
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K ==> L[production]
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G --> |production <br>deployment| K
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end
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```
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In this case, deploy the `staging` branch to your staging environment.
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To deploy to pre-production, create a merge request from the `staging` branch to the `pre-prod` branch.
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Go live by merging the `pre-prod` branch into the `production` branch.
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This workflow, where commits only flow downstream, ensures that everything is tested in all environments.
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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 `production` with a merge request.
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In this case, do not delete the feature branch yet.
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If `production` passes automatic testing, you then merge the feature branch into the other branches.
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If this is not possible because more manual testing is required, you can send merge requests from the feature branch to the downstream branches.
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## Release branches with GitLab flow
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You should work with release branches only if you need to release software to
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the outside world. In this case, each branch contains a minor version, such as
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`2.3-stable` or `2.4-stable`:
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```mermaid
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graph LR
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A:::main ===> B((main))
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B:::main ==> C((main))
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C:::main ==> D((main))
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D:::main ==> E((main))
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A((main)) ----> F((2.3-stable)):::first
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F --> G((2.3-stable)):::first
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C -.-> |cherry-pick| G
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D --> H((2.4-stable)):::second
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classDef main fill:#f4f0ff,stroke:#7b58cf
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classDef first fill:#e9f3fc,stroke:#1f75cb
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classDef second fill:#ecf4ee,stroke:#108548
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```
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Create stable branches using `main` as a starting point, and branch as late as possible.
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By doing this, you minimize the length of time during which you have to apply bug fixes to multiple branches.
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After announcing a release branch, only add serious bug fixes to the branch.
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If possible, first merge these bug fixes into `main`, and then cherry-pick them into the release branch.
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If you start by merging into the release branch, you might forget to cherry-pick them into `main`, and then you'd encounter the same bug in subsequent releases.
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Merging into `main` and then cherry-picking into release is called an "upstream first" policy, which is also practiced by [Google](https://www.chromium.org/chromium-os/chromiumos-design-docs/upstream-first) and [Red Hat](https://www.redhat.com/en/blog/a-community-for-using-openstack-with-red-hat-rdo).
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Every time you include a bug fix in a release branch, increase the patch version (to comply with [Semantic Versioning](https://semver.org/)) by setting a new tag.
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Some projects also have a stable branch that points to the same commit as the latest released branch.
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In this flow, it is not common to have a production branch (or Git flow `main` branch).
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## Merge/pull requests with GitLab flow
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Merge or pull requests are created in a Git management application. They ask an assigned person to merge two branches.
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Tools such as GitHub and Bitbucket choose the name "pull request", because the first manual action is to pull the feature branch.
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Tools such as GitLab and others choose the name "merge request", because the final action is to merge the feature branch.
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This article refers to them as merge requests.
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If you work on a feature branch for more than a few hours, share the intermediate result with the rest of your team.
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To do this, create a merge request without assigning it to anyone.
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Instead, mention people in the description or a comment, for example, "/cc @mark @susan."
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This indicates that the merge request is not ready to be merged yet, but feedback is welcome.
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Your team members can comment on the merge request in general or on specific lines with line comments.
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The merge request serves as a code review tool, and no separate code review tools should be needed.
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If the review reveals shortcomings, anyone can commit and push a fix.
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Usually, the person to do this is the creator of the merge request.
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The diff in the merge request automatically updates when new commits are pushed to the branch.
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When you are ready for your feature branch to be merged, assign the merge request to the person who knows most about the codebase you are changing.
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Also, mention any other people from whom you would like feedback.
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After the assigned person feels comfortable with the result, they can merge the branch.
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If the assigned person does not feel comfortable, they can request more changes or close the merge request without merging.
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In GitLab, it is common to protect the long-lived branches, such as the `main` branch, so [most developers can't modify them](../user/permissions.md).
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So, if you want to merge into a protected branch, assign your merge request to someone with the
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Maintainer role.
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After you merge a feature branch, you should remove it from the source control software.
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In GitLab, you can do this when merging.
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Removing finished branches ensures that the list of branches shows only work in progress.
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It also ensures that if someone reopens the issue, they can use the same branch name without causing problems.
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NOTE:
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When you reopen an issue you need to create a new merge request.
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## Issue tracking with GitLab flow
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GitLab flow is a way to make the relation between the code and the issue tracker more transparent.
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Any significant change to the code should start with an issue that describes the goal.
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Having a reason for every code change helps to inform the rest of the team and to keep the scope of a feature branch small.
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In GitLab, each change to the codebase starts with an issue in the issue tracking system.
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If there is no issue yet, create the issue if the change requires more than an hour's work.
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In many organizations, raising an issue is part of the development process because they are used in sprint planning.
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The issue title should describe the desired state of the system.
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For example, the issue title "As an administrator, I want to remove users without receiving an error" is better than "Administrators can't remove users."
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When you are ready to code, create a branch for the issue from the `main` branch.
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This branch is the place for any work related to this change.
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NOTE:
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The name of a branch might be dictated by organizational standards.
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When you are done or want to discuss the code, open a merge request.
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A merge request is an online place to discuss the change and review the code.
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If you open the merge request but do not assign it to anyone, it is a [draft merge request](../user/project/merge_requests/drafts.md).
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These are used to discuss the proposed implementation but are not ready for inclusion in the `main` branch yet.
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Start the title of the merge request with `[Draft]`, `Draft:` or `(Draft)` to prevent it from being merged before it's ready.
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When you think the code is ready, assign the merge request to a reviewer.
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The reviewer can merge the changes when they think the code is ready for inclusion in the `main` branch.
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When they press the merge button, GitLab merges the code and creates a merge commit that makes this event visible later on.
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Merge requests always create a merge commit, even when the branch could be merged without one.
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This merge strategy is called "no fast-forward" in Git.
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After the merge, delete the feature branch, because it is no longer needed.
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In GitLab, this deletion is an option when merging.
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Suppose that a branch is merged but a problem occurs and the issue is reopened.
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In this case, it is no problem to reuse the same branch name, because the first branch was deleted when it was merged.
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At any time, there is at most one branch for every issue.
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It is possible that one feature branch solves more than one issue.
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## Linking and closing issues from merge requests
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Link to issues by mentioning them in commit messages or the description of a merge request, for example, "Fixes #16" or "Duck typing is preferred. See #12."
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GitLab then creates links to the mentioned issues and creates comments in the issues linking back to the merge request.
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To automatically close linked issues, mention them with the words "fixes" or "closes," for example, "fixes #14" or "closes #67." GitLab closes these issues when the code is merged into the default branch.
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If you have an issue that spans across multiple repositories, create an issue for each repository and link all issues to a parent issue.
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## Squashing commits with rebase
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With Git, you can use an interactive rebase (`rebase -i`) to squash multiple commits into one or reorder them.
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This feature helps you replace a couple of small commits with a single commit, or if you want to make the order more logical:
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```shell
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pick c6ee4d3 add a new file to the repo
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pick c3c130b change readme
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# Rebase 168afa0..c3c130b onto 168afa0
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#
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# Commands:
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# p, pick = use commit
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# r, reword = use commit, but edit the commit message
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# e, edit = use commit, but stop for amending
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# s, squash = use commit, but meld into previous commit
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# f, fixup = like "squash", but discard this commit's log message
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# x, exec = run command (the rest of the line) using shell
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#
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# These lines can be re-ordered; they are executed from top to bottom.
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#
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# If you remove a line here THAT COMMIT WILL BE LOST.
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#
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# However, if you remove everything, the rebase will be aborted.
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#
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# Note that empty commits are commented out
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~
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~
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~
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"~/demo/gitlab-ce/.git/rebase-merge/git-rebase-todo" 20L, 673C
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```
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However, you should avoid rebasing commits you have pushed to a remote server if you have other active contributors in the same branch.
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Because rebasing creates new commits for all your changes, it can cause confusion because the same change would have multiple identifiers.
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It would cause merge errors for anyone working on the same branch because their history would not match with yours. It can be really troublesome for the author or other contributors.
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Also, if someone has already reviewed your code, rebasing makes it hard to tell what changed after the last review.
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You should never rebase commits authored by other people unless you've agreed otherwise.
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Not only does this rewrite history, but it also loses authorship information.
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Rebasing prevents the other authors from being attributed and sharing part of the [`git blame`](https://git-scm.com/docs/git-blame).
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If a merge involves many commits, it may seem more difficult to undo.
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You might consider solving this by squashing all the changes into one commit just before merging by using the GitLab [Squash-and-Merge](../user/project/merge_requests/squash_and_merge.md) feature.
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Fortunately, you can undo a merge with all its commits.
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The way to do this is by reverting the merge commit.
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Preserving this ability to revert a merge is a good reason to always use the "no fast-forward" (`--no-ff`) strategy when you merge manually.
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NOTE:
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If you revert a merge commit and then change your mind, revert the revert commit to redo the merge.
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Git does not allow you to merge the code again otherwise.
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## Reducing merge commits in feature branches
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Having lots of merge commits can make your repository history messy.
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Therefore, you should try to avoid merge commits in feature branches.
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Often, people avoid merge commits by just using rebase to reorder their commits after the commits on the `main` branch.
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Using rebase prevents a merge commit when merging `main` into your feature branch, and it creates a neat linear history.
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However, as discussed in [the section about rebasing](#squashing-commits-with-rebase), you should avoid rebasing commits in a feature branch that you're sharing with others.
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Rebasing could create more work, as every time you rebase, you may need to resolve the same conflicts.
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Sometimes you can reuse recorded resolutions (`rerere`), but merging is better, because you only have to resolve conflicts once.
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Atlassian has [a more thorough explanation of the tradeoffs between merging and rebasing](https://www.atlassian.com/blog/git/git-team-workflows-merge-or-rebase) on their blog.
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A good way to prevent creating many merge commits is to not frequently merge `main` into the feature branch.
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There are three reasons to merge in `main`: utilizing new code, resolving merge conflicts, and updating long-running branches.
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If you need to use some code that was introduced in `main` after you created the feature branch, you can often solve this by just cherry-picking a commit.
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If your feature branch has a merge conflict, creating a merge commit is a standard way of solving this.
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NOTE:
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Sometimes you can use `.gitattributes` to reduce merge conflicts.
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For example, you can set your changelog file to use the [union merge driver](https://git-scm.com/docs/gitattributes#gitattributes-union) so that multiple new entries don't conflict with each other.
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The last reason for creating merge commits is to keep long-running feature branches up-to-date with the latest state of the project.
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The solution here is to keep your feature branches short-lived.
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Most feature branches should take less than one day of work.
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If your feature branches often take more than a day of work, try to split your features into smaller units of work.
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If you need to keep a feature branch open for more than a day, there are a few strategies to keep it up-to-date.
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One option is to use continuous integration (CI) to merge in `main` at the start of the day.
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Another option is to only merge in from well-defined points in time, for example, a tagged release.
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You could also use [feature toggles](https://martinfowler.com/bliki/FeatureToggle.html) to hide incomplete features so you can still merge back into `main` every day.
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NOTE:
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Don't confuse automatic branch testing with continuous integration.
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Martin Fowler makes this distinction in [an article about feature branches](https://martinfowler.com/bliki/FeatureBranch.html):
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"\[People\] say they are doing CI because they are running builds, perhaps using a CI server, on every branch with every commit.
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That's continuous building, and a Good Thing, but there's no *integration*, so it's not CI."
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In conclusion, you should try to prevent merge commits, but not eliminate them.
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Your codebase should be clean, but your history should represent what actually happened.
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Developing software happens in small, messy steps, and it is OK to have your history reflect this.
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You can use tools to view the network graphs of commits and understand the messy history that created your code.
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If you rebase code, the history is incorrect, and there is no way for tools to remedy this because they can't deal with changing commit identifiers.
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## Commit often and push frequently
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Another way to make your development work easier is to commit often.
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Every time you have a working set of tests and code, you should make a commit.
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Splitting up work into individual commits provides context for developers looking at your code later.
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Smaller commits make it clear how a feature was developed. They help you roll back to a specific good point in time, or to revert one code change without reverting several unrelated changes.
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Committing often also helps you share your work, which is important so that everyone is aware of what you are working on.
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You should push your feature branch frequently, even when it is not yet ready for review.
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By sharing your work in a feature branch or [a merge request](#mergepull-requests-with-gitlab-flow), you prevent your team members from duplicating work.
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Sharing your work before it's complete also allows for discussion and feedback about the changes. This feedback can help improve the code before it gets to review.
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## How to write a good commit message
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A commit message should reflect your intention, not just the contents of the commit.
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You can see the changes in a commit, so the commit message should explain why you made those changes:
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```shell
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# This commit message doesn't give enough information
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git commit -m 'Improve XML generation'
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# These commit messages clearly state the intent of the commit
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git commit -m 'Properly escape special characters in XML generation'
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```
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An example of a good commit message is: "Combine templates to reduce duplicate code in the user views."
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The words "change," "improve," "fix," and "refactor" don't add much information to a commit message.
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For more information, please see Tim Pope's excellent [note about formatting commit messages](https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html).
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To add more context to a commit message, consider adding information regarding the
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origin of the change. For example, the URL of a GitLab issue, or a Jira issue number,
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containing more information for users who need in-depth context about the change.
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For example:
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```plaintext
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Properly escape special characters in XML generation.
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Issue: gitlab.com/gitlab-org/gitlab/-/issues/1
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```
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## Testing before merging
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In old workflows, the continuous integration (CI) server commonly ran tests on the `main` branch only.
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Developers had to ensure their code did not break the `main` branch.
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When using GitLab flow, developers create their branches from this `main` branch, so it is essential that it never breaks.
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Therefore, each merge request must be tested before it is accepted.
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CI software like Travis CI and GitLab CI/CD show the build results right in the merge request itself to simplify the process.
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There is one drawback to testing merge requests: the CI server only tests the feature branch itself, not the merged result.
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Ideally, the server could also test the `main` branch after each change.
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However, retesting on every commit to `main` is computationally expensive and means you are more frequently waiting for test results.
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Because feature branches should be short-lived, testing just the branch is an acceptable risk.
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If new commits in `main` cause merge conflicts with the feature branch, merge `main` back into the branch to make the CI server re-run the tests.
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As said before, if you often have feature branches that last for more than a few days, you should make your issues smaller.
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## Working with feature branches
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When creating a feature branch, always branch from an up-to-date `main`.
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If you know before you start that your work depends on another branch, you can also branch from there.
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If you need to merge in another branch after starting, explain the reason in the merge commit.
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If you have not pushed your commits to a shared location yet, you can also incorporate changes by rebasing on `main` or another feature branch.
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Do not merge from upstream again if your code can work and merge cleanly without doing so.
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Merging only when needed prevents creating merge commits in your feature branch that later end up littering the `main` history.
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