[simonchrz]

Stacked on #701, so this shows two commits until that merges. Only the second one, 42a071b, is new. Draft because it adds a table and I'd like your view on the design first.

What

storage.retention.keep_latest: N now also applies to oci. Blobs are cached under their digest, so there are no versions to order. Instead the proxy keeps the blobs of the N images of a repository that a tag most recently pointed at.

My case: a mirror schedule pulls homeassistant/home-assistant:beta every few minutes, with a 3 day retention rule for that repository. With keep_latest: 2 the current beta and the one before it stay cached, however old they are.

How

• New table image_manifests (migration 024): per repository and manifest digest, the digests it references and when a tag last pointed at it.
• The manifest serve path and the mirror record a manifest when it is served. A pull by tag sets the tag time, a pull by digest does not. Referrers tags (sha256-<hex>, .sig, .att) do not count as tags.
• The retention sweep takes the N newest tagged manifests of a repository, follows index -> platform manifests -> config and layers, and keeps those blobs. It then prunes the records of images that are no longer among the newest (1 hour grace).
• Nothing is recorded unless keep_latest is set and a retention rule can evict oci blobs. With keep_latest back at 0 the next sweep clears the table.

Limits

• An image counts once its tag was pulled or mirrored with keep_latest set, and its blobs are known once its platform manifest was served too. A client that already has the image does not pull that manifest again, so those blobs expire by their rule as before.
• Images pulled only by digest are not counted.
• The count is per repository, not per tag. With several tags in use, N has to be at least that high.
• Helm charts over OCI and Homebrew bottles go through the same handler, so they count as images too.
• storage.max_size can still evict a kept blob, as in Add storage.retention.keep_latest to keep the newest versions #701.

Questions

• Is a table for this fine, or would you rather read the references from the cached manifests at sweep time? I went with the table because the manifest cache has its own expiry and the sweep would have to parse every cached manifest.
• Per repository or per tag? Per tag is closer to what a user expects with many tags, but needs the tag name stored as well.

Tests

End to end through a fake registry in internal/server/retention_keep_latest_oci_test.go (keep 0, 1 and 2, pruning, digest pulls, no oci rule), plus tests for the table and the serve path. go test ./... and golangci-lint run pass locally. I did not run the Postgres tests locally.

Summary by CodeRabbit

• New Features
  • OCI image storage retention now supports keep_latest, retaining blobs referenced by the newest tagged images in each repository. Shared blobs remain available while referenced by a retained image. Tag pulls, including HEAD requests, count toward retention; images pulled only by digest do not.
• Documentation
  • Clarified how OCI images are counted and retained, how manifest references are tracked, and that setting keep_latest to 0 keeps no images.

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No actionable comments were generated in the recent review.

Walkthrough

This change adds OCI image-manifest tracking and extends storage.retention.keep_latest to retain blobs referenced by the newest tagged images in each repository. Retention sweeps prune old manifest records and keep image blobs according to the configured count.

Changes: Keep Latest Retention

Layer / File(s)	Summary
Image-manifest storage and traversal internal/database/schema.go, internal/database/image_manifests.go, internal/database/image_manifests_test.go, internal/database/database_test.go, docs/architecture.md	Adds the image_manifests table and database operations to record manifest references, find digests reachable from the newest tagged images, list repositories, and prune older records.
Record manifests from OCI requests and mirrors internal/handler/container_image_refs.go, internal/handler/container_manifest.go, internal/handler/container_mirror.go, internal/handler/container.go, internal/handler/handler.go, internal/handler/profile.go, internal/handler/profile_test.go, internal/handler/container_image_refs_test.go, internal/server/server.go	Records OCI manifest references and tag times during manifest requests and mirror runs. Proxy configuration carries the image-retention count and enables tracking for OCI.
Apply OCI keep-latest retention internal/retention/retention.go, internal/retention/keep_latest_test.go, internal/server/retention.go, internal/server/retention_keep_latest_oci_test.go, internal/server/retention_keep_latest_test.go, config.example.yaml, docs/configuration.md	Extends keep-latest eligibility and retention sweeps to OCI images. Sweeps prune old manifest records and retain blobs referenced by the newest tagged images. Tests and documentation describe the OCI behavior and configuration.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant ContainerClient
  participant serveManifest
  participant writeManifest
  participant recordImageManifest
  participant DB
  ContainerClient->>serveManifest: requests a manifest by tag or digest
  serveManifest->>writeManifest: passes manifest and requested reference
  writeManifest->>recordImageManifest: records the manifest
  recordImageManifest->>DB: stores references and tag time

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Possibly related issues

• git-pkgs/proxy#410 — This change adds OCI tag-based retention for proxied and mirrored images; the issue also requests hosted OCI retention and push support, which this change does not cover.

Possibly related PRs

• git-pkgs/proxy#701 — Adds storage.retention.keep_latest for cached package versions, while this change extends the setting to OCI images.

Suggested labels: enhancement

Suggested reviewers: pinguinfuss, andrew

Merge Risk: Minimal · up to 05650

This change extends keep_latest retention to OCI images. Earlier review concerns have been addressed, and no concrete merge-blocking issue remains.

Security architecture risk: Low · up to 05650

The change remains scoped to image retention, with existing repository and denylist controls preserved. Concurrent cleanup can nevertheless discard recently refreshed protection, weakening cached-image availability during an upstream outage.

Retained concerns

• Medium · reliability · inferred: Pruning can erase a concurrently refreshed image's protection. It first captures reachable manifests, then separately deletes excluded rows using recorded_at. An existing row can become newly tagged after that capture yet remain eligible for deletion because the UPSERT advances tagged_at without refreshing recorded_at. Since pruning precedes blob protection selection, otherwise-expired blobs can lose their intended exemption. Future pulls may then require an unavailable upstream, weakening failure containment. The one-hour grace protects newly inserted rows, not these refreshes; recent blob access or mirroring still prevents immediate expiry.

Security review details

Security Blast Radius

• inferred — A caller already able to pull a tag can influence image ordering in that canonical repository, while an upstream publisher supplies manifest references. The traced retention queries remain repository-scoped and protect only already-cached artifacts in that repository; a supplied digest does not select another repository's records.

Trust Boundaries and Controls

• observed — The recording hook remains behind repository routing and tag/digest denylist checks. Repository identity comes from the resolved cache name, not manifest content. Recorded references accept supported digest syntax, discard duplicates and return no reference list above 4096 entries; database statements bind values as parameters.

Resilience and Maintainability Implications

• observed — Protection-query errors conservatively keep artifacts for that sweep, and artifact clearing transactionally rechecks expiry and queues deletion. Manifest recording is instead best-effort: read or write failures are logged without preventing the response, so a successful pull alone does not prove durable protection history exists.

Hardening Proposals

• proposed — Coordinate per-repository recording, graph selection and pruning through a refresh-aware transactional or epoch protocol. Validate the interleaving where an old excluded manifest becomes newly tagged during cleanup, including preservation of its recorded descendants.

Pre-merge checks: 4

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: retaining blobs for the newest container images through keep_latest.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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• config.example.yaml
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• internal/config/retention.go
• internal/config/retention_test.go
• internal/database/database_test.go
• internal/database/image_manifests.go
• internal/database/image_manifests_test.go
• internal/database/retention.go
• internal/database/retention_test.go
• internal/database/schema.go
• internal/handler/cargo.go
• internal/handler/container.go
• internal/handler/container_image_refs.go
• internal/handler/container_image_refs_test.go
• internal/handler/container_manifest.go
• internal/handler/container_mirror.go
• internal/handler/go.go
• internal/handler/go_test.go
• internal/handler/handler.go
• internal/handler/npm.go
• internal/handler/profile.go
• internal/handler/profile_test.go
• internal/handler/pypi.go
• internal/retention/keep_latest_test.go
• internal/retention/retention.go
• internal/server/retention.go
• internal/server/retention_keep_latest_oci_test.go
• internal/server/retention_keep_latest_test.go
• internal/server/retention_test.go
• internal/server/server.go

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Actionable comments posted: 2

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• Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix all issues

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Inline comments:
Review comments at @internal/server/retention.go:
- Line 277: Update the digest selection used by the retention flow around
NewestImageDigests so tag representations for the same image count as one kept
image, and retain every representation required by each kept image, including an
index and its platform manifests. Preserve the keep_latest limit over images
rather than individual digests.

Review comments at @internal/server/server.go:
- Line 311: Update NewMirrorProxy to initialize proxy.KeepLatestImages with the
existing keepLatestImages configuration helper, ensuring mirrored images honor
the keep_latest setting.

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[andrew]

The table is the right call, since the manifest cache expires on its own schedule and would lose the old images this is meant to protect. Per repository is right too: per tag would keep N images for every pinned version tag, which amounts to never evicting a version-tagged repository.

One thing needs fixing before this goes in. A Docker or containerd pull does not count the image until its tag is requested a second time. Those clients send HEAD /manifests/<tag> and then GET /manifests/<digest>. For a tag that is not cached, headManifest returns a manifest with no body and stores nothing, so recordImageManifest finds no record and no refs and returns without noting the tag. The GET by digest then records the manifest with tagged_at = 0. An image pulled once per tag, such as a pinned version on a deploy host, is never kept; only a later HEAD of the same tag marks it.

The mirror path and clients that GET the tag are fine, and those are the flows the tests cover: pullImage GETs the tag, and the HEAD case in TestContainerPullAgainMovesTagTimeForward runs after a GET has already recorded the manifest.

A tag sighting could insert a row with empty refs, with RecordImageManifest filling refs on conflict when the stored value is empty. Please add a test that pulls HEAD-tag then GET-digest through the handler and checks the blobs survive a sweep.

[simonchrz]

Thanks, you're right. Fixed in 056504d as you suggested: a tag seen through a HEAD is now recorded with empty refs, and RecordImageManifest fills in refs on conflict when the stored value is empty (the tag time still only moves forward). TestSweepRetentionKeepsBlobsOfImagesPulledByHead pulls HEAD-tag, then the index, the platform manifest and the blobs by digest through the handler, and checks that the newest image's blobs survive a sweep and the older one's don't. TestRecordImageManifestFillsInReferences covers the upsert on both databases.