ci(docker): use H200 runner for builds and add nightly GHCR workflow

[slin1237]

Summary

Use the H200 GPU runner for Docker builds (replacing single-core ubuntu-latest) and add a nightly build that publishes to GitHub Container Registry.

What changed

• .github/workflows/release-docker.yml: Changed runs-on from ubuntu-latest to ["8-gpu-h200"] for faster builds
• .github/workflows/nightly-docker.yml (new): Nightly Docker build at 06:00 UTC pushing to ghcr.io/lightseekorg/smg:nightly

Why

The H200 runner is only used during nightly benchmarks (08:00 UTC), leaving it idle the rest of the time. Docker builds on ubuntu-latest are slow due to limited compute. Moving builds to H200 leverages its many cores for significantly faster builds.

The nightly GHCR image provides a daily snapshot without cluttering Docker Hub releases. Uses a single :nightly tag that gets overwritten each run to avoid storage accumulation.

How

• Nightly scheduled at 06:00 UTC — 2 hours before benchmarks at 08:00 UTC to avoid runner contention
• Uses QEMU + buildx for multi-platform (linux/amd64, linux/arm64)
• GHA build cache (type=gha) for layer caching
• Concurrency group prevents overlapping runs
• if: github.repository == 'lightseekorg/smg' guard prevents fork execution
• GITHUB_TOKEN (built-in) with packages: write permission for GHCR — no extra secrets needed

Test plan

• Trigger workflow_dispatch on nightly-docker workflow to verify GHCR push
• Trigger workflow_dispatch on release-docker workflow to verify H200 build
• Confirm no runner contention between nightly docker (06:00) and benchmarks (08:00)

Summary by CodeRabbit

• New Features

  • Nightly Docker images are now automatically built and published daily.

• Chores

  • Updated Docker build infrastructure for improved performance and consistency.

[gemini-code-assist]

Note

Gemini is unable to generate a summary for this pull request due to the file types involved not being currently supported.

[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request introduces a new nightly Docker build workflow scheduled to run daily at 6:00 UTC and updates the existing release Docker workflow to use a GPU runner (8-gpu-h200) instead of the standard Ubuntu runner for multi-architecture image builds.

Changes

Cohort / File(s)	Summary
New Nightly Docker Workflow .github/workflows/nightly-docker.yml	Introduces a new workflow triggered on schedule (6:00 UTC daily) and manual dispatch. Builds and pushes multi-architecture Docker images (linux/amd64, linux/arm64) to ghcr.io/lightseekorg/smg:nightly on a GPU runner with GitHub Actions caching enabled.
Updated Release Docker Workflow .github/workflows/release-docker.yml	Changes the job runner from ubuntu-latest to 8-gpu-h200 GPU runner.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• ci: add Docker image release workflow #431 — Both PRs modify Docker CI workflows and touch .github/workflows/release-docker.yml, establishing direct workflow continuity.

Suggested labels

ci

Suggested reviewers

• CatherineSue
• key4ng
• XinyueZhang369

Poem

🐰 A nightly build hops into view,
GPU runners working, shiny and new,
Docker images dance across archs so wide,
With caching for speed and GitHub's great pride! 🐇✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the two main changes: switching to H200 runner for Docker builds and adding a nightly GHCR workflow.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch slin/docker-build

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In @.github/workflows/nightly-docker.yml:
- Around line 22-24: Remove the redundant job-level permissions block (the lines
defining permissions: contents: read and packages: write) because these
duplicate the workflow-level permissions already defined; locate the job's
permissions stanza (the permissions: contents: read and packages: write entries)
and delete it so only the workflow-level permissions remain, or alternatively
keep the block if you intentionally want explicit job-level override—choose one
approach and ensure there is no duplicate permissions block.