home-network-k3s-impl/runbooks/cnpg-archiving.md

cnpg-archiving — WAL archiving is stuck, or a Postgres cluster has no recoverability point

Alerts: CNPGWALArchiveBacklog (warning, 1h) and CNPGNoRecoverabilityPoint (warning, 6h) File: platform/cnpg/alerts.yaml, group platform-health.cnpg Expressions:

max by (namespace, pod) (cnpg_collector_pg_wal_archive_status{value="ready"}) > 0
max by (namespace, job)  (cnpg_collector_first_recoverability_point) == 0

What this means here — and why it is an AVAILABILITY incident, not just a backup one

pg_wal/archive_status holds one marker per WAL segment: .ready = written but not yet archived, .done = archived and safe to recycle. A healthy archiver drains .ready within seconds, so a persistently non-zero ready count means barman-cloud-wal-archive is failing.

Two consequences, and the second one is the emergency:

1. There is no continuous archive, so PITR is broken (R-IDP-05 / R-STATE-03).
2. archive_mode=on means Postgres will NOT recycle an unarchived WAL segment. pg_wal grows without bound until the data PVC fills and the postmaster PANICs. pg_wal shares the data PVC on every Cluster here — no walStorage: is configured on any of them — so there is no separate volume to absorb it.

This is measured, not theoretical. Prod ran from bootstrap to 2026-09-07 with endpointURL: TBD-PROD-S3-BACKUP-ENDPOINT: all three Clusters at ContinuousArchiving=False with barman-cloud-wal-archive: exit status 4 and firstRecoverabilityPoint: null, for 38+ hours, with no alert of any kind — found by hand. On keycloak-db that was 17 unarchived segments / ~268 MiB on a 5 GiB PVC, growing ~6.8 MiB/h ≈ 29 days to disk-full (about 579 MiB already burned by 2026-09-07). The rule recorded verbatim: "Never leave a placeholder here, and treat ContinuousArchiving=False on this Cluster as an availability incident, not a backup one."

CNPGWALArchiveBacklog is "the one that would have caught the 2026-09-06 incident within the hour instead of 38 hours later." > 0 with for: 1h — not a count threshold — because for requires the condition at every evaluation for the full hour, so a write burst resets the timer while a genuinely stuck archiver never returns to zero. A > 5 threshold would have delayed semaphore-db indefinitely: its backlog sits at 3 because it writes almost nothing.

The two alerts are NOT the same statement

CNPGWALArchiveBacklog is about the mechanism and is per-pod (each instance has its own pg_wal on its own PVC; a > 0 shape is safe per-pod, and pod names the instance to go look at).

CNPGNoRecoverabilityPoint is about DR coverage and is per-CLUSTER, grouped by (namespace, job). That grouping is a fix, dated 2026-09-12: only the primary reads the backup catalogue, so a replica reports a hard 0 forever. Grouped by pod, this == 0 fired permanently on all six replicas while all three Clusters were healthy. Verified live: old max by (namespace, pod) (...) == 0 → 6 series (keycloak-db-1/-3, nextcloud-db-1/-3, semaphore-db-1/-3); new max by (namespace, job) (...) == 0 → empty — and not vacuously so: forcing the metric to 0 for one primary yields exactly one series. job is the grouping label because the metric carries no cnpg.io/cluster label; the operator creates one PodMonitor per Cluster, so prometheus-operator derives job="<namespace>/<cluster>": keycloak/keycloak-db, nextcloud-db/nextcloud-db, semaphore-db/semaphore-db. namespace alone happens to work today but would let two Clusters in one namespace mask each other.

Practical note: if you see this alert firing on pods rather than per cluster, the per-cluster aggregation is not deployed on this cluster yet — check the deployed PrometheusRule before treating it as a real loss of DR.

Severity is warning on purpose. A database heading for disk-full deserves weeks of lead time, and this repo has been burned by a permanently-firing critical (the VPNTunnelDown post-mortem). The critical tier for this failure mode is PersistentVolumeAlmostFull, which fires only when the outage is genuinely imminent.

Running the commands in this runbook

kubectl does not work on the operator workstation. The toolchain lives only in the pinned dev container, and the host's k3s-oidc context hangs on a browser prompt once its token expires — that hang is not the cluster being down. Every command below runs as:

infra/devcontainer/dev.sh run bash -c 'kubectl --context k3s-prod get nodes'

Always pass --context k3s-prod explicitly. dev.sh merges both clusters into one kubeconfig and defaults its current-context to k3s-dev, so a command without --context silently answers about the wrong cluster. (CLUSTER=prod infra/devcontainer/dev.sh run kubectl ... is equivalent.) Do not run two dev.sh invocations at once — they share one container and interfere.

USE FULLY-QUALIFIED RESOURCE NAMES, ALWAYS. Three CRDs on this cluster register the kind Backup: longhorn.io/v1beta2, postgresql.cnpg.io/v1 and velero.io/v1. The bare short name resolves to Longhorn's, which holds zero objects — so kubectl get backup -A prints "No resources found" on a cluster holding 6 Velero backups and 27 CNPG backups. Verified on prod 2026-09-13. Reading that as "the backups are gone" and acting on it turns a false negative into real data loss. Write backups.velero.io, backups.postgresql.cnpg.io, clusters.postgresql.cnpg.io, settings.longhorn.io, volumes.longhorn.io, nodes.longhorn.io.

Mutating kubectl (apply, patch, annotate, rollout) and flux reconcile are blocked for agents here: every durable change goes through git (git push origin main is the deploy). Where this runbook gives a mutating command it is for an operator, and it says so.

First commands

The three Clusters' archiving and recoverability status — the single most informative command:

infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod get clusters.postgresql.cnpg.io -A \
     -o custom-columns=NS:.metadata.namespace,NAME:.metadata.name,READY:.status.readyInstances,PRIMARY:.status.currentPrimary,ARCHIVING:.status.conditions[?\(@.type==\"ContinuousArchiving\"\)].status,LASTBACKUP:.status.conditions[?\(@.type==\"LastBackupSucceeded\"\)].status,FIRSTPITR:.status.firstRecoverabilityPoint'

The archiver's actual error text — exit status 4 and its cause live here:

infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod -n keycloak logs keycloak-db-2 -c postgres --tail=200 2>&1 | grep -i archive | tail -30'

The backlog on disk, per instance:

infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod -n keycloak exec keycloak-db-2 -c postgres -- bash -c \
     "ls /var/lib/postgresql/data/pgdata/pg_wal/archive_status | grep -c ready; du -sh /var/lib/postgresql/data/pgdata/pg_wal; df -h /var/lib/postgresql/data"'

The backups that exist — fully-qualified, or you will be told there are none:

infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod get backups.postgresql.cnpg.io -A; echo; \
   kubectl --context k3s-prod get scheduledbackups.postgresql.cnpg.io -A'

kubectl get backup -A prints "No resources found" on this cluster even with 27 CNPG backups present: three CRDs register the kind Backup (longhorn.io, postgresql.cnpg.io, velero.io) and the short name resolves to Longhorn's, which holds zero. Verified on prod 2026-09-13. Never decide a recovery action from the short name.

The object-store configuration, which is where the fault usually is:

infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod get clusters.postgresql.cnpg.io -n keycloak keycloak-db -o yaml | sed -n "/backup:/,/^  [a-z]/p"'

grep -nE "CNPG_BACKUP_PATH|S3_BACKUP_ENDPOINT|S3_BACKUP_REGION|BACKUP_CREDENTIALS_SUFFIX" clusters/base/cluster-vars.yaml clusters/prod/kustomization.yaml

Likely causes, most likely first

1. A wrong or placeholder object-store endpoint / path / credential

The recorded cause of the 38-hour incident: prod ran with endpointURL: TBD-PROD-S3-BACKUP-ENDPOINT. The placeholder was deliberately loud because "base defaults are the DEV values, so an OMITTED op means prod silently inherits a dev address — far worse than a failed apply". Live prod values to expect: CNPG_BACKUP_PATH = s3://k3s-prod-backup/barman, S3_BACKUP_ENDPOINT = https://7ce452a1b3d6c86daf2c020edcb82d37.r2.cloudflarestorage.com, S3_BACKUP_REGION = auto, BACKUP_CREDENTIALS_SUFFIX = -prod, retention 30d, WAL compression gzip, maxParallel: 2. Remediation: fix it in git and push; Flux applies and the archiver drains on its own.

2. R2-specific S3 incompatibilities

Cloudflare R2 rejects things MinIO tolerates. The two that are mandatory elsewhere in this platform and worth checking here: region must be exactly auto, and AWS-SDK checksum headers are rejected with HTTP 400 InvalidArgument. See /runbooks/backup-failure for the full R2 story, including the Velero plugin's x-amz-tagging NotImplemented failure.

3. Credentials expired or mis-scoped

A SOPS-encrypted Secret selected by BACKUP_CREDENTIALS_SUFFIX. Standing rule from the OIDC incident: non-secret, environment-specific values must NOT live inside an encrypted Secret — ${BASE_DOMAIN} substitution can never reach inside one. Keep endpoints and paths in cluster-vars, tokens in the Secret.

4. Egress is blocked

Default-deny is the baseline. The database namespaces need outbound HTTPS to R2. Cross-read /runbooks/denied-flows.

5. A fresh Cluster that has not made its first base backup

firstRecoverabilityPoint reads null until the first base backup lands; the for: 6h exists exactly to keep a legitimate cold start quiet. Base backups are staggered: keycloak 01:00, nextcloud 02:00, semaphore 04:00 (Velero at 03:00). If a Cluster is hours old, wait.

6. Scaling out made it worse

Noted honestly: scaling a Cluster while archive_mode=on with a failing archive_command multiplies the disk-full clock. Do not add instances as a remedy here.

When to escalate or stop

• Treat ContinuousArchiving=False as an availability incident with a countdown. Compute the runway: free bytes on the data PVC ÷ WAL growth rate. At ~6.8 MiB/h on a 5 GiB PVC that is weeks; on a busier database it is days.
• NEVER delete WAL segments by hand. It destroys the database. This is the one irreversible mistake available in this runbook.
• Do not delete the .ready marker files. Same outcome.
• Do not expand the PVC and stop there. It buys time and hides the fault.
• Do not scale the Cluster while archiving is failing.
• Verify before any restore that firstRecoverabilityPoint is non-null and backups.postgresql.cnpg.io shows completed backups. Prod's healthy state on 2026-09-13 was: all three Clusters ContinuousArchiving=True, LastBackupSucceeded=True, firstRecoverabilityPoint 2026-09-07, 27 backups (9 per cluster) completing daily, with one historical failure (semaphore-db-daily-20260905130918). That is what "good" looks like.
• Escalate to the operator for credential or endpoint changes, and for any restore.

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Source of truth: runbooks/cnpg-archiving.md. Index: /runbooks/ Records: platform/cnpg/alerts.yaml header (the 2026-09-06 incident, the measured fill rate, and the 2026-09-12 aggregation-scope fix with its live promtool proof); platform/keycloak/postgres-cluster.yaml; commit 32d6766 (the R2 decision).