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ci(runner): bump the embedded actions runner automatically #212

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176 changes: 176 additions & 0 deletions .github/workflows/runner-bump.yml
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name: Runner Bump

# Keeps ephemerd's embedded GitHub Actions runner current. GitHub deprecates
# old runner versions and then refuses their connections, which silently stalls
# every job on the affected pool (the macOS pool once ran ZERO jobs for a week on
# a stale runner), so this must not depend on someone remembering to bump it.
#
# Daily, it asks the GitHub release API for the newest non-draft,
# non-prerelease actions/runner release. If that is newer than RunnerVersion in
# mage/download/download.go, `go run ./mage/runnerbump` rewrites every pin site
# (RunnerVersion, the five runner entries of pinnedSHA256, and ARG
# RUNNER_VERSION in images/runner-ci-*/Dockerfile) with checksums taken from
# the release API's per-asset `digest` field, and this job opens a PR. It never
# merges: review and merge stay manual.
#
# Idempotency: one fixed branch, bot/actions-runner-bump, regenerated from main
# on every run. No new release -> nothing happens. Same release as the open PR
# -> nothing is pushed (so CI is not retriggered on the self-hosted fleet). A
# newer release -> the branch is force-pushed and the existing PR is retitled
# and re-described rather than a second one opened. If main reaches the latest
# release some other way (a manual bump), the stale bot PR is closed. The
# branch is machine-owned: do not push commits to it, they will be overwritten.
#
# Token: PRs opened with the default GITHUB_TOKEN do not trigger CI (GitHub's
# recursion guard), and the ephpm org also has "Allow GitHub Actions to create
# and approve pull requests" switched off, so the default token cannot open the
# PR at all. Configure a GitHub App and this job uses its installation token
# instead, which both opens the PR and lets ci.yml run on it:
# - repo or org variable BOT_APP_CLIENT_ID the App's Client ID
# - repo or org secret BOT_APP_PRIVATE_KEY a private key (.pem) of the App
# The App needs Contents: read & write and Pull requests: read & write, and must
# be installed on ephpm/ephemerd. Without those, the job falls back to
# GITHUB_TOKEN: it still pushes the branch, and fails with instructions if the
# PR cannot be opened.
#
# Runs on GitHub-hosted ubuntu-latest so it never takes a slot on the
# self-hosted fleet.

on:
schedule:
# Daily, off the top of the hour.
- cron: "23 7 * * *"
workflow_dispatch:
inputs:
version:
description: "Exact actions/runner version to bump to (e.g. 2.338.0). Empty = latest stable release."
required: false
type: string

permissions:
contents: write
pull-requests: write

concurrency:
group: runner-bump
cancel-in-progress: false

env:
BRANCH: bot/actions-runner-bump

jobs:
bump:
runs-on: ubuntu-latest
timeout-minutes: 20
steps:
- name: Mint GitHub App token
id: app
if: vars.BOT_APP_CLIENT_ID != ''
uses: actions/create-github-app-token@v3
with:
client-id: ${{ vars.BOT_APP_CLIENT_ID }}
private-key: ${{ secrets.BOT_APP_PRIVATE_KEY }}
permission-contents: write
permission-pull-requests: write

- uses: actions/checkout@v6
with:
fetch-depth: 1
token: ${{ steps.app.outputs.token || github.token }}

- uses: actions/setup-go@v6
with:
go-version-file: go.mod
# runnerbump is stdlib-only; restoring the repo's module cache would
# cost more than it saves.
cache: false

- name: Bump the runner pins if a newer release exists
id: bump
env:
GH_TOKEN: ${{ github.token }}
VERSION: ${{ inputs.version || '' }}
run: |
set -euo pipefail
go run ./mage/runnerbump -version "$VERSION" -body-out "$RUNNER_TEMP/pr-body.md"

- name: Validate the edit
if: steps.bump.outputs.bump == 'true'
run: |
set -euo pipefail
unformatted=$(gofmt -l mage/)
if [ -n "$unformatted" ]; then
echo "::error::gofmt reports unformatted files after the bump: $unformatted"
exit 1
fi
go build ./mage/...
git --no-pager diff --stat

- name: Open or update the bump PR
if: steps.bump.outputs.bump == 'true'
env:
GH_TOKEN: ${{ steps.app.outputs.token || github.token }}
USING_APP: ${{ steps.app.outputs.token && 'true' || 'false' }}
CURRENT: ${{ steps.bump.outputs.current }}
LATEST: ${{ steps.bump.outputs.latest }}
run: |
set -euo pipefail
fail() { echo "::error::$*"; exit 1; }

files=(mage/download/download.go images/runner-ci-linux/Dockerfile images/runner-ci-macos/Dockerfile images/runner-ci-windows/Dockerfile)
title="fix(runner): bump embedded actions runner to ${LATEST}"

git config user.name "github-actions[bot]"
git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
git checkout -B "$BRANCH"
git add "${files[@]}"
git commit -q -m "$title" \
-m "Bump the embedded actions/runner from ${CURRENT} to ${LATEST}: RunnerVersion and the five runner pinnedSHA256 entries in mage/download/download.go, and ARG RUNNER_VERSION in the CI runner images. Checksums are the release API's asset digests." \
-m "Automated by .github/workflows/runner-bump.yml." \
|| fail "nothing to commit after the bump; runnerbump and this list of files are out of step"

# Push only when the bumped files differ from what the bot branch
# already carries, so a rerun for the same release is a no-op and
# does not retrigger CI.
if git fetch -q --depth=1 origin "refs/heads/${BRANCH}" 2>/dev/null \
&& git diff --quiet FETCH_HEAD HEAD -- "${files[@]}"; then
echo "${BRANCH} already carries runner ${LATEST}; not pushing"
else
git push --force origin "HEAD:refs/heads/${BRANCH}" || fail "pushing ${BRANCH} failed"
echo "pushed ${BRANCH} (runner ${LATEST})"
fi

pr=$(gh pr list --head "$BRANCH" --base main --state open --json number --jq '.[0].number // empty')
if [ -n "$pr" ]; then
gh pr edit "$pr" --title "$title" --body-file "$RUNNER_TEMP/pr-body.md" \
|| fail "updating PR #${pr} failed"
echo "::notice::updated PR #${pr} for runner ${LATEST}"
exit 0
fi

if ! gh pr create --base main --head "$BRANCH" --title "$title" --body-file "$RUNNER_TEMP/pr-body.md"; then
compare="${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}/compare/main...${BRANCH}?expand=1"
if [ "$USING_APP" != "true" ]; then
fail "could not open the PR with GITHUB_TOKEN. Set the BOT_APP_CLIENT_ID variable and BOT_APP_PRIVATE_KEY secret (see the header of runner-bump.yml), or enable 'Allow GitHub Actions to create and approve pull requests' in the repo's Actions settings. The branch is pushed; open it by hand: ${compare}"
fi
fail "opening the PR failed; the branch is pushed: ${compare}"
fi
echo "::notice::opened a PR for runner ${LATEST}"

- name: Close a bot PR that main has caught up with
# Only on unpinned runs: a dispatch for an older explicit version must
# not close a PR for a newer one.
if: steps.bump.outputs.bump == 'false' && !inputs.version
env:
GH_TOKEN: ${{ steps.app.outputs.token || github.token }}
CURRENT: ${{ steps.bump.outputs.current }}
run: |
set -euo pipefail
pr=$(gh pr list --head "$BRANCH" --base main --state open --json number --jq '.[0].number // empty')
if [ -z "$pr" ]; then
echo "no open bot PR; nothing to do"
exit 0
fi
gh pr close "$pr" --delete-branch \
--comment "main is already on actions/runner ${CURRENT}, the latest stable release, so this bump is no longer needed."
echo "::notice::closed stale PR #${pr}"
5 changes: 4 additions & 1 deletion mage/download/download.go
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Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,10 @@ const (
//
// Hashes are the upstream-published checksums for the versions pinned in the
// const block above:
// - runner: release body "SHA" markers (github.com/actions/runner)
// - runner: the release API's per-asset "digest" (github.com/actions/runner),
// cross-checked against the release body "SHA" markers. Bumped
// automatically by .github/workflows/runner-bump.yml via mage/runnerbump;
// keep the runner pin sites in the shape runnerbump expects.
// - cni: <asset>.tgz.sha256
// - containerd: <asset>.tar.gz.sha256sum
// - runc: runc.sha256sum (per-arch runc.<arch> lines)
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