Default Branch Migration

Instructions on how to migrate the default branch from master to main.

Default Branch Migration

This document outlines steps needed to migrate the default branch of your repo from master to main.

Note: This document is currently a work in progress.

If you have questions about the process, reach out to the GitHub Management Team on the #github-management channel on slack or open an issue in the kubernetes/org repo.

Prerequisites

  • Create an issue in your repo to track the branch rename. You can paste this checklist in the issue body.

  • If you are not a root approver for the repo, assign a root approver for approval.

  • Once the issue has been approved, send a notice to your SIG’s mailing list about the potential branch rename.

Changes pre-rename

Make the following changes before renaming the branch the master branch.

Note: There might be additional changes required that have not been covered in this checklist.

Anytime

These changes are non-disruptive and can be made anytime before renaming the branch.

Just before rename

These changes are disruptive and should be made just before renaming the branch.

  • For periodic prowjobs, or any prowjob that mentions the master branch in base_ref, update them to the main branch. Ensure that these changes happen in lock-step with the branch rename (jobs triggered in between landing these changes and renaming the branch will fail).

    • For bootstrap-based jobs, ensure the branch is explicitly specified, e.g. kubernetes/foo=main. kubernetes/test-infra#20667 may eventually allow for non-disruptive changes.
    • For pod-utils based jobs, ensure the branch is explicitly specified, e.g. base_ref: main. kubernetes/test-infra#20672 may eventually allow for non-disruptive changes.
  • If a prowjob mentions master in its name, rename the job to not include the branch name, e.g. pull-repo-verify-master -> pull-repo-verify. status-reconciler should automatically migrate PR status contexts to the new job name, and retrigger accordingly, but we have anecdotally found it sometimes misses changes.

    • NOTE: our infrastructure doesn’t understand the concept of job renames, so from the perspective of e.g. https://testgrid.k8s.io the job will appear to have lost history and start from scratch.
  • If a prowjob calls scripts or code in your repo that explicitly reference master, update all references to use main, or auto-detect the remote branch

    • e.g. using git to auto-detect
    # for existing clones, update their view of the remote
    git fetch origin
    git remote set-head origin -a
    # for new clones, or those updated as above, this prints "main" post-rename
    echo $(git symbolic-ref refs/remotes/origin/HEAD)
    
    • e.g. using github’s api to auto-detect
    # gh is https://github.com/cli/cli, this will print "main" post-rename
    gh api /repos/kubernetes-sigs/slack-infra | jq -r .default_branch
    
  • If the repo has netlify configured for it, ask a member of the GitHub Management Team to rename the master branch to main in the netlify site config. It can’t be controlled through the netlify config in the repo.

Approval

  • Once all non-disruptive tasks have been completed and disruptive tasks have been identified, assign the GitHub Management team (@kubernetes/owners) for approval.

Rename the default branch

  • Rename the default branch from master to main using the GitHub UI by following the official instructions.

Changes post-rename

After the default branch has been renamed to main, make the following changes.

Note: There might be additional changes required that have not been covered in this checklist.

Prowjobs

  • If a prowjob still references the master branch in the branches field, remove the master branch (see kubernetes/test-infra#20669 for an example).

Prow config

  • If the milestone_applier prow config references the master branch, remove it from the config.

  • If the branch_protection prow config references the master branch, remove it from the config.

Other

  • If any docs reference the master branch, update to main (URLs will be automatically redirected).

  • Ensure that CI and PR tests work fine.

    • If there are any outstanding PRs you can /approve to merge, do so to verify that presubmits and postsubmits work as expected
  • Trial the local development experience with a pre-rename clone.

  • Send a notice about the branch rename to your SIG’s mailing list. Include the link to the GitHub instructions to rename your local branch.