## Context
The mailserver stack holds everything valuable and hard to recreate:
243M of maildirs, dovecot/rspamd state, and the DKIM private key that
signs outbound mail. Today the only defense is the LVM thin-pool
snapshots on the PVE host (7-day retention, storage-class scope only)
— there is no app-level backup. Infra/.claude/CLAUDE.md mandates that
every proxmox-lvm(-encrypted) app ship a NFS-backed backup CronJob,
and the mailserver stack was the only one still out of compliance.
Loss of mailserver-data-encrypted without backups = total loss of all
stored mail plus a DKIM key rotation (which requires a DNS update and
breaks signature verification on every message in transit for the TTL
window). Unacceptable for a service people actually use.
Trade-offs considered:
- mysqldump-style single-file dump vs rsync snapshot — maildirs are
millions of small files, not a DB export. rsync --link-dest gives
incremental weekly snapshots for ~10% of the cost of a full copy.
- RWO PVC read-only mount — the underlying PVC is ReadWriteOnce, so
the backup Job has to co-locate with the mailserver pod. vaultwarden
solves this with pod_affinity; mirrored here.
- Image choice — alpine + apk add rsync matches vaultwarden's pattern
and keeps the container image small.
## This change
Adds `kubernetes_cron_job_v1.mailserver-backup` + NFS PV/PVC to the
mailserver module. Runs daily at 03:00 (avoids the 00:30 mysql-backup
and 00:45 per-db windows, and the */20 email-roundtrip cadence). The
job rsyncs /var/mail, /var/mail-state, /var/log/mail into
/srv/nfs/mailserver-backup/<YYYY-WW>/ with --link-dest against the
previous week for space-efficient incrementals. 8-week retention.
Data layout (flowed through from the deployment's subPath mounts so
the rsync tree matches the mailserver's own on-disk layout):
PVC mailserver-data-encrypted (RWO, 2Gi)
├─ data/ (subPath) → pod's /var/mail → backup/<week>/data/
├─ state/ (subPath) → pod's /var/mail-state → backup/<week>/state/
└─ log/ (subPath) → pod's /var/log/mail → backup/<week>/log/
Safety:
- PVC mounted read-only (volume.persistent_volume_claim.read_only
AND all three volume_mounts set read_only=true) so a backup-script
bug cannot corrupt maildirs.
- pod_affinity on app=mailserver + topology_key=hostname forces the
Job pod onto the same node holding the RWO PVC attachment.
- set -euxo pipefail + per-directory existence guard so a missing
subPath short-circuits cleanly instead of silently no-op'ing.
Metrics pushed to Pushgateway match the mysql-backup/vaultwarden-backup
convention (job="mailserver-backup"):
backup_duration_seconds, backup_read_bytes, backup_written_bytes,
backup_output_bytes, backup_last_success_timestamp.
Alert rules added in monitoring stack, mirroring Mysql/Vaultwarden:
- MailserverBackupStale — 36h threshold, critical, 30m for:
- MailserverBackupNeverSucceeded — critical, 1h for:
## Reproduce locally
1. cd infra/stacks/mailserver && ../../scripts/tg plan
Expected: 3 to add (cronjob + NFS PV + PVC), unrelated drift on
deployment/service is pre-existing.
2. ../../scripts/tg apply --non-interactive \
-target=module.mailserver.module.nfs_mailserver_backup_host \
-target=module.mailserver.kubernetes_cron_job_v1.mailserver-backup
3. cd ../monitoring && ../../scripts/tg apply --non-interactive
4. kubectl create job --from=cronjob/mailserver-backup \
mailserver-backup-test -n mailserver
5. kubectl wait --for=condition=complete --timeout=300s \
job/mailserver-backup-test -n mailserver
6. Expected: test pod co-locates with mailserver on same node
(k8s-node2 today), rsync writes ~950M to
/srv/nfs/mailserver-backup/<YYYY-WW>/, Pushgateway exposes
backup_output_bytes{job="mailserver-backup"}.
## Test Plan
### Automated
$ kubectl get cronjob -n mailserver mailserver-backup
NAME SCHEDULE TIMEZONE SUSPEND ACTIVE LAST SCHEDULE AGE
mailserver-backup 0 3 * * * <none> False 0 <none> 3s
$ kubectl create job --from=cronjob/mailserver-backup \
mailserver-backup-test -n mailserver
job.batch/mailserver-backup-test created
$ kubectl wait --for=condition=complete --timeout=300s \
job/mailserver-backup-test -n mailserver
job.batch/mailserver-backup-test condition met
$ kubectl logs -n mailserver job/mailserver-backup-test | tail -5
=== Backup IO Stats ===
duration: 80s
read: 1120 MiB
written: 1186 MiB
output: 947.0M
$ kubectl run nfs-verify --rm --image=alpine --restart=Never \
--overrides='{...nfs mount /srv/nfs...}' \
-n mailserver --attach -- ls -la /nfs/mailserver-backup/
947.0M /nfs/mailserver-backup/2026-15
$ curl http://prometheus-prometheus-pushgateway.monitoring:9091/metrics \
| grep mailserver-backup
backup_duration_seconds{instance="",job="mailserver-backup"} 80
backup_last_success_timestamp{instance="",job="mailserver-backup"} 1.776554641e+09
backup_output_bytes{instance="",job="mailserver-backup"} 9.92315701e+08
backup_read_bytes{instance="",job="mailserver-backup"} 1.175027712e+09
backup_written_bytes{instance="",job="mailserver-backup"} 1.244254208e+09
$ curl -s http://prometheus-server/api/v1/rules \
| jq '.data.groups[].rules[] | select(.name | test("Mailserver"))'
MailserverBackupStale: (time() - kube_cronjob_status_last_successful_time{cronjob="mailserver-backup",namespace="mailserver"}) > 129600
MailserverBackupNeverSucceeded: kube_cronjob_status_last_successful_time{cronjob="mailserver-backup",namespace="mailserver"} == 0
### Manual Verification
1. Wait for the scheduled 03:00 run tonight; verify
`kubectl get job -n mailserver` shows a new completed job.
2. Check that `backup_last_success_timestamp` advances past today.
3. Confirm `MailserverBackupNeverSucceeded` did not fire.
4. Next week (week 16), confirm `--link-dest` builds hardlinks vs
2026-15 (size delta should drop from ~950M to ~the actual churn).
## Deviations from mysql-backup pattern
- Image: alpine + rsync (mirrors vaultwarden — mysql's `mysql:8.0`
base is not applicable for a filesystem rsync).
- pod_affinity: required for RWO PVC co-location (mysql uses its own
MySQL service for network access; mailserver must mount the PVC).
- Metric push via wget (mirrors vaultwarden; alpine has wget, not curl).
- Week-folder layout with --link-dest rotation: rsync pattern, closer
to the PVE daily-backup script than mysql's single-file gzip dumps.
[ci skip]
Closes: code-z26
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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