[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. Retention applies when an OCI retention rule enables it.
• 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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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: OCI 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, internal/retention/retention.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/server/retention.go, internal/server/retention_keep_latest_oci_test.go, internal/server/retention_keep_latest_test.go, internal/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: 4 (Complex) | ~45 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 the manifest and requested reference
  writeManifest->>recordImageManifest: records the image manifest
  recordImageManifest->>DB: stores references and tag time

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Suggested reviewers: andrew

Merge Risk: Minimal · up to 7a867

This change extends keep_latest retention to OCI images by tracking manifest references and tag times. No unresolved issues were identified, and the earlier review findings have been addressed.

Security architecture risk: Low · up to 7a867

The design keeps existing access controls and repository isolation. One bounded concurrency flaw can erase newly refreshed image history during pruning, allowing images intended to remain available for recovery or rollback to expire.

Retained concerns

• Medium · reliability · inferred: Pruning can discard a concurrent tag refresh. After selecting its protected manifests, PruneImageManifests deletes other rows using their original recorded_at. If an older, excluded manifest is successfully tagged before that DELETE, RecordImageManifest advances tagged_at but leaves recorded_at unchanged, so the refreshed row still qualifies for deletion. The later keeper can then protect the previous image rather than the newly tagged one. When only the tag was requested and its blobs remain age-expired, those blobs can become uncached, undermining offline recovery or rollback. Newly inserted rows receive grace, but refreshed old rows do not; the deletion transaction rechecks artifact age, not image membership.

Security review details

Security Blast Radius

• inferred — A caller able to pull an allowed tag can influence retention ordering for that repository. The new reference traversal and pruning remain scoped by repository PURL; the inspected paths do not grant that caller cross-repository deletion or new upstream-selection authority.

Trust Boundaries and Controls

• observed — The existing GET path verifies manifest bodies against requested and advertised digests before caching. Mirror traversal invokes the same manifest routes, retaining their digest-denylist checks before recording; tag history is committed only after a successful mirror walk.

Resilience and Maintainability Implications

• inferred — The concurrency concern affects cache availability rather than granting content integrity or authorization privileges. Refetching can recover missing content while upstream remains available, but cannot substitute for retained images during an upstream outage.

Hardening Proposals

• proposed — Coordinate recording, reference filling and pruning through a shared repository-scoped concurrency protocol, or condition deletion on an unchanged row revision, so pruning cannot discard updates made after protected-set selection.

Pre-merge checks: 4

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title "Keep the blobs of the newest container images with keep_latest" matches the main change. The PR adds OCI image support for storage.retention.keep_latest, which retains blobs referenced by t…
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.

Full details: Title check

Explanation

The title "Keep the blobs of the newest container images with keep_latest" matches the main change. The PR adds OCI image support for storage.retention.keep_latest, which retains blobs referenced by the N most recently tagged images per repository. The changeset covers the image_manifests table, retention sweep logic, handler tracking, and config docs, all of which serve this goal. The title is specific and concise, and a teammate scanning history would understand the primary change.

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• config.example.yaml
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• 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
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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.