see: https://k8s.dev/rename, kubernetes/org#2222

Checklist below added from kubernetes/community@198374d

Prerequisites

• Ensure that your repo has low PR volume (<20 open PRs) and
  less number of periodic jobs. The branch rename will re-trigger
  prow on all open PRs, which will cause a huge spike in the CI load.

  • We have zero periodic jobs directly consuming this repo
  • We have < 10 PRs open now (17:14 PST 2021-03-15)

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

  • This is the issue

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

  • I am a root approver

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

  • Notice here: https://groups.google.com/g/kubernetes-sig-testing/c/Gi0A_TJsP7A

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.

• If a prowjob triggers on the master branch (branches field
  of the prowjob), add the main branch to the list
  (see [prep kubernetes/org jobs for default branch rename kubernetes/test-infra#20665] for an example).

  • N/A: we only use one branch and don't specify it wherever possible

• If the [milestone_applier] prow config references the master branch,
  add the main branch to the config (see [Prep kubernetes/k8s.io for default branch rename kubernetes/test-infra#20675] for an example).

  • N/A: we don't use milestone applier

• If the [branch_protection] prow config references the master branch,
  add the main branch to the config.

  • N/A: we only use the automatic branch protection based on prowjobs

Just before rename

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

• If a prowjob mentions the master branch in base_ref,
  update it to the main branch. For a periodic job, ensure that
  the branch is renamed between periodic job runs.

  • N/A we have no jobs that mention branches of this repo.

• If a prowjob mentions master in its name, rename the job to
  to not include the branch name. [status-reconciler] should automatically
  migrate the PR status contexts to the new job name but this has not been tested yet.
  The job with the new name will also appear as a different job in Testgrid.

  • N/A we have no jobs that mention branches of this repo.

• If a prowjob calls scripts or code in your repo that explicitly
  reference master, update all references to use main.

  • N/A we don't do this.

• 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.

  • We will need to do this.
  • This is done.

Approval

• Once all non-disruptive tasks have been completed and disruptive tasks
  have been identified, assign the GitHub Management team ([@kubernetes/owners])
  for approval.
  • tracking: switch default branch to main #2120 (comment) (see below)

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 [Update kubernetes/org job configs post default-branch-rename kubernetes/test-infra#20669] for an example).
  • N/A we have no jobs that mention branches of this repo.

Prow config

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

  • N/A we don't use milestone_applier here

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

  • N/A we don't have any repo specific branch_protection config (just the automated standard configuration)

Other

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

  • This is done.

• Ensure that CI and PR tests work fine.

  • Look fine so far.

• Trial the local development experience with a pre-rename clone.

  • Nothing in our development experience is branch specific, I just needed to switch from master to main as expected.

• 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].

/assign