Added CI step to publish ActivityPub image publicly

[sagzy]

ref https://linear.app/ghost/issue/PROD-1662

• to facilitate self-hosting, we're publishing a Docker image for ActivityPub to a public registry (Github Container Registry)
• the public image will then be used in a Docker Compose file to run Ghost and ActivityPub services

[coderabbitai]

Walkthrough

This change updates the GitHub Actions CI/CD workflow configuration to support publishing ActivityPub Docker images to both a private registry (europe-docker.pkg.dev) and a public registry (ghcr.io). The workflow now generates Docker metadata separately for each registry, with the public registry steps running only on the main branch. Docker image build and push steps are adjusted to use the appropriate metadata and login credentials for each registry. The Migrations Docker image process remains unchanged and continues to target only the private registry. No changes were made to exported or public code entities.

Possibly related PRs

• Fixed cicd deploy pipeline #537: Modifies the same workflow file to adjust deployment step conditions, similar to this PR's changes to Docker image build and push logic.
• Added push step to the future main registry #406: Updates Docker image metadata handling and private registry push steps, which aligns with this PR's enhancements and registry handling.
• Updated GCP registry tags #465: Alters Docker metadata tagging in the workflow, related to this PR's changes in Docker metadata steps and publishing strategy.

Suggested labels

ricardo.ghost.is

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📜 Recent review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 3296e8e and ed83592.

📒 Files selected for processing (1)

• .github/workflows/cicd.yml (5 hunks)

🔇 Additional comments (9)

.github/workflows/cicd.yml (9)

16-19: Grant packages: write for Docker publishing
Adding packages: write alongside contents: read ensures the GITHUB_TOKEN can push container images to GHCR.

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56-58: Expose ActivityPub image version as a job output
The new activitypub_docker_version output correctly references the private metadata step’s version for downstream deploys.

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62-83: Generate Docker metadata for private registry
Splitting out a dedicated metadata-action step for the private Artifact Registry with comprehensive OCI labels looks correct and maintains parity with the existing migrations flow.

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84-103: Generate Docker metadata for public registry
The new conditional metadata-action step (only on main) for GHCR is properly configured with semver and SHA tags and mirrors the label set.

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125-127: Use private metadata outputs in the local build step
The build step now leverages steps.activitypub-docker-metadata-private.outputs.tags and labels for caching via load: true.

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147-153: Authenticate to GCP Artifact Registry
The GCP auth + docker/login-action for europe-docker.pkg.dev is correctly gated for both PRs and main pushes.

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155-162: Authenticate to GitHub Container Registry
Logging into ghcr.io on main with the GITHUB_TOKEN allows the public push step to succeed.

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163-172: Push ActivityPub image to private registry
The push step correctly references the private metadata tags/labels and is conditioned identically to the auth step. Platforms are explicitly set to linux/amd64.

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173-182: Push ActivityPub image to public registry
The new public push step uses GHCR metadata outputs, runs only on main, and matches the private flow’s platform settings.

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[rmgpinto]

LGTM