Second identical registry incident on 2026-04-19 (first 2026-04-13): the
infra-ci:latest image index resolved to child manifests whose blobs had been
garbage-collected out from under the index. Pipelines P366→P376 all exited
126 "image can't be pulled". Hot fix (a05d63e / 6371e75 / c113be4) restored
green CI but left the underlying bug unaddressed.
Root cause: cleanup-tags.sh rmtrees tag dirs on the registry VM daily at
02:00, registry:2's GC (Sunday 03:25) walks OCI index children imperfectly
(distribution/distribution#3324 class). Nothing verified pushes end-to-end;
nothing probed the registry for fetchability; nothing caught orphan indexes.
Phase 1 — Detection:
- .woodpecker/build-ci-image.yml: after build-and-push, a verify-integrity
step walks the just-pushed manifest (index + children + config + every
layer blob) via HEAD and fails the pipeline on any non-200. Catches
broken pushes at the source.
- stacks/monitoring: new registry-integrity-probe CronJob (every 15m) and
three alerts — RegistryManifestIntegrityFailure,
RegistryIntegrityProbeStale, RegistryCatalogInaccessible — closing the
"registry serves 404 for a tag that exists" gap that masked the incident
for 2+ hours.
- docs/post-mortems/2026-04-19-registry-orphan-index.md: root cause,
timeline, monitoring gaps, permanent fix.
Phase 2 — Prevention:
- modules/docker-registry/docker-compose.yml: pin registry:2 → registry:2.8.3
across all six registry services. Removes the floating-tag footgun.
- modules/docker-registry/fix-broken-blobs.sh: new scan walks every
_manifests/revisions/sha256/<digest> that is an image index and logs a
loud WARNING when a referenced child blob is missing. Does NOT auto-
delete — deleting a published image is a conscious decision. Layer-link
scan preserved.
Phase 3 — Recovery:
- build-ci-image.yml: accept `manual` event so Woodpecker API/UI rebuilds
don't need a cosmetic Dockerfile edit (matches convention from
pve-nfs-exports-sync.yml).
- docs/runbooks/registry-rebuild-image.md: exact command sequence for
diagnosing + rebuilding after an orphan-index incident, plus a fallback
for building directly on the registry VM if Woodpecker itself is down.
- docs/runbooks/registry-vm.md + .claude/reference/service-catalog.md:
cross-references to the new runbook.
Out of scope (verified healthy or intentionally deferred):
- Pull-through DockerHub/GHCR mirrors (74.5% hit rate, no 404s).
- Registry HA/replication (single-VM SPOF is a known architectural
choice; Synology offsite covers RPO < 1 day).
- Diun exclude for registry:2 — not applicable; Diun only watches
k8s (DIUN_PROVIDERS_KUBERNETES=true), not the VM's docker-compose.
Verified locally:
- fix-broken-blobs.sh --dry-run on a synthetic registry directory correctly
flags both orphan layer links and orphan OCI-index children.
- terraform fmt + validate on stacks/monitoring: success (only unrelated
deprecation warnings).
- python3 yaml.safe_load on .woodpecker/build-ci-image.yml and
modules/docker-registry/docker-compose.yml: both parse clean.
Closes: code-4b8
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
7cb44d7264