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Code Review: Migrate workflows to Blacksmith runners

Summary

This PR migrates GitHub Actions workflows to use Blacksmith's faster runners and optimized Docker layer caching. The migration affects 5 workflow files and introduces 6 unpinned third-party actions that GitHub Advanced Security has flagged.

Detailed Review

1. Security Issues (Critical)

Unpinned Third-Party Actions

GitHub Advanced Security correctly flagged 6 instances of unpinned Blacksmith actions. Using unpinned tags (like v1, v2) instead of commit hashes creates supply chain security risks:

Files affected:

• .github/workflows/docker-build-push.yml:34 - useblacksmith/setup-docker-builder@v1
• .github/workflows/docker-build-push.yml:44 - useblacksmith/build-push-action@v2
• .github/workflows/release.yml:81 - useblacksmith/setup-docker-builder@v1
• .github/workflows/release.yml:91 - useblacksmith/build-push-action@v2
• .github/workflows/test.yml:86 - useblacksmith/setup-docker-builder@v1
• .github/workflows/test.yml:88 - useblacksmith/build-push-action@v2

Recommendation: Pin all third-party actions to specific commit SHAs for supply chain security:

# Instead of:
uses: useblacksmith/setup-docker-builder@v1

# Use:
uses: useblacksmith/setup-docker-builder@<commit-sha>  # v1

This is a best practice for production workflows to prevent against compromised action repositories. Note that GitHub's own actions (actions/checkout@v6, etc.) are maintained by GitHub and generally considered safer, but third-party actions should always be pinned.

Fix unpinned actions →

2. Workflow Changes Assessment

Positive Changes:

✅ Concurrency control added (.github/workflows/ci.yml:12-14)

• Prevents redundant workflow runs on the same ref
• cancel-in-progress: true saves CI minutes by canceling outdated runs
• This is a best practice for reducing CI costs and wait times

✅ Runner upgrades are consistent

• ubuntu-latest → blacksmith-2vcpu-ubuntu-2404 (standard jobs)
• ubuntu-latest → blacksmith-4vcpu-ubuntu-2404 (release job that needs more power)
• Appropriate runner sizing based on workload

✅ Docker action replacements are functional

• docker/setup-buildx-action@v3 → useblacksmith/setup-docker-builder@v1
• docker/build-push-action@v6 → useblacksmith/build-push-action@v2
• These are drop-in replacements with cache optimization

Cache Strategy Change:

⚠️ Explicit GHA cache removed (.github/workflows/test.yml:93-94)

- cache-from: type=gha
- cache-to: type=gha,mode=max

According to the PR description, Blacksmith provides automatic cache handling that's "4x faster" and "colocated." However, this introduces a vendor lock-in concern:

• Risk: If you ever need to migrate away from Blacksmith, you'll lose the cache optimization and need to reconfigure caching
• Mitigation: This is an acceptable trade-off if the performance gains justify it
• Consideration: Monitor actual performance improvements to validate the 4x claim

3. Workflow Correctness

✅ All workflows maintain functional equivalence:

• Docker build contexts, platforms (linux/amd64,linux/arm64), and push behavior unchanged
• Image tagging logic preserved
• Job dependencies intact
• Permissions properly scoped (principle of least privilege maintained)

✅ No breaking changes to workflow interfaces:

• workflow_call inputs/outputs unchanged
• Environment variables preserved
• Artifact naming consistent

4. CI/CD Best Practices

Well Done:

• ✅ Proper permission scoping (e.g., permissions: contents: read at job level)
• ✅ Conditional job execution (if: github.event_name != 'merge_group')
• ✅ Matrix strategy maintained for multi-app builds
• ✅ Secret handling via secrets: inherit (appropriate for reusable workflows)

Areas for Consideration:

⚠️ Runner availability/reliability

• Blacksmith is a third-party service - ensure you have SLA guarantees
• Consider fallback strategy if Blacksmith has an outage
• Monitor for any differences in runner behavior vs GitHub-hosted runners

⚠️ Cost monitoring

• "First 3,000 minutes per month are free" - ensure you have alerting set up when approaching limits
• Understand cost structure beyond free tier

5. Performance & Resource Efficiency

Expected improvements (per PR description):

• 2x faster compute (Blacksmith hardware)
• 4x faster cache access
• 40x faster Docker builds (layer cache sharing)

Recommendation: Set up benchmarking to validate these claims:

• Compare job durations before/after migration
• Monitor cache hit rates
• Track overall CI pipeline duration

Consider adding workflow run time reporting or dashboards to measure ROI.

6. Testing & Reliability

✅ All CI checks passing:

• Buf checks: passed
• Code coverage: 55.44% (slight improvement of +0.05%)
• No test failures introduced

✅ PR already approved by @tac0turtle

⚠️ Testing recommendation:
After merge, monitor the next few CI runs closely to ensure:

• Cache warming works correctly on first runs
• Multi-platform builds (linux/amd64,linux/arm64) complete successfully
• Docker layer cache sharing actually reduces build times
• No flakiness introduced by runner changes

Final Recommendation

Overall assessment: This is a reasonable infrastructure migration with measurable benefits, but has one critical security issue that should be addressed.

Before merging:

1. [CRITICAL] Pin all useblacksmith/* actions to commit SHAs (not just version tags)
2. Ensure team has access to Blacksmith dashboard for observability
3. Set up cost/usage monitoring alerts

After merging:

1. Monitor first ~10 CI runs for any issues
2. Benchmark actual performance improvements
3. Document rollback procedure if needed

Approval status: Functionally sound, but security hardening needed for production readiness.

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.38%. Comparing base (30a3e24) to head (6f19ec7).

@@           Coverage Diff           @@
##             main    #3035   +/-   ##
=======================================
  Coverage   55.38%   55.38%           
=======================================
  Files         117      117           
  Lines       11674    11674           
=======================================
  Hits         6466     6466           
  Misses       4483     4483           
  Partials      725      725           

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