# ks4 backup strategy (2026-08)

Audience: anyone with root on ks4 who needs to know **what is protected,
where, by which tool, and how to check it**. Details live in the linked
docs; this page is the map.

## Two tools, no more

| tool | job | why this one |
|---|---|---|
| **`incus copy --refresh`** | replicate whole instances (ready-to-start copies) | ZFS-incremental, native to the platform, restores are `incus start` |
| **restic** | off-site backups to S3 (files, database dumps, instance trees) | dedup + encryption, local metadata cache → a night costs only the churn ([restic-backup.md](ks4/restic-backup.md)) |

plakar was evaluated first and replaced (its nightly cost scaled with
tree size — [PlakarKorp/plakar#2338](https://github.com/PlakarKorp/plakar/issues/2338));
the old backup server **ks2 is being retired** (decommission by
Sep 30, 2026 — [ks2/plan.md](ks2/plan.md)): it still holds an ageing
copy of the instances until the nuc leg below takes over.

**Status 2026-08-28**: the local replica leg and the S3 data leg are
live. The **nuc pull leg is waiting for FTTH** (expected before end of
September); until it lands, the ks2 push is re-enabled as an interim
off-site copy of the instances. Backing up instance *images* to S3 was
designed and shelved — S3 holds the data, the databases and the incus
configuration, which is what a rebuild needs.

## The map

```
 ks4 (OVH)                                           off-site
 ┌────────────────────────────────────────────┐
 │  live instances       pool `data` (sda)    │
 │  nextcloud, seafile, mail, git, ...        │
 │        │                                   │
 │        │ 01:00  incus copy --refresh       │     nuc (home LAN, via WireGuard)
 │        ▼                                   │     ┌───────────────────────────┐
 │  replicas (stopped)   pool `backup` (sdb)  │────▶│ 05:00 incus copy (pull)   │
 │  project `backup`     ready to start       │     │ pool `ks4backup` (USB)    │
 │                                            │     └───────────────────────────┘
 │  ────────────────────────────────────────  │
 │                                            │     OVH Object Storage (S3, sbg)
 │  05:00 restic-backup.sh                    │     ┌───────────────────────────┐
 │    • DB dumps (MariaDB/PostgreSQL, auto)   │────▶│ bucket restic-data        │
 │    • incus config + global DB dump         │     │  everything needed to     │
 │    • data trees (restic-paths)             │     │  rebuild: dumps + data    │
 │                                            │     └───────────────────────────┘
 │  Sun 14:00 restic-maintenance.sh           │
 │    • prune + check (rotating full verify)  │
 └────────────────────────────────────────────┘
```

Two different kinds of protection, on purpose:

- **instances** (the running systems) are protected by *replication* —
  a ready-to-start copy on ks4's second disk and, after FTTH, on nuc.
  Restoring one is `incus copy` + `incus start`.
- **the data inside them** (files, databases, incus configuration) is
  protected by *backup* — encrypted, deduplicated, versioned on S3,
  independent of ks4 and of the disks. Restoring means recreating the
  container (its config is in the S3 dumps, its install steps are in
  this repo) and pouring the data back.

Backing up whole instance images to S3 as well was designed
([ks4/restic-backup.md](ks4/restic-backup.md) §6) and shelved: it
duplicates data already covered, and the replication legs already give
instances two homes.

## Schedule (root crontab on ks4)

| when | what | log |
|---|---|---|
| 01:00 daily | `incus-copy.sh -p backup -s backup` — refresh all replicas onto sdb | `/var/log/incus-copy.log` |
| 02:00 daily | `incus-copy.sh -d ks2 -m push` — interim off-site replicas, until the nuc leg replaces it | `/var/log/incus-copy.log` |
| 03:00 daily | instance snapshots (incus profile, 7-day expiry) — what keeps the refreshes incremental | `incus info <inst>` |
| 05:00 daily | `restic-backup.sh` — dumps + data trees → S3 | `/var/log/restic-backup.log` |
| 05:00 daily (nuc) | nuc pulls all replicas over WireGuard | nuc: `/var/log/incus-copy-ks4.log` |
| Sun 14:00 | `restic-maintenance.sh` — prune (capped), structure check, 1/52 data verification | `/var/log/restic-maintenance.log` |
| 1st of month 06:00 / quarterly 15th | seafile GC dry-run report / real GC ([ks4/seafile-gc.md](ks4/seafile-gc.md)) | `/var/log/seafile-gc.log` |

Retention on S3: 14 daily, 8 weekly, 6 monthly snapshots.

## "Did last night work?" — the 30-second check

```sh
grep -aE "done \(rc=|FAILED" /var/log/incus-copy.log | tail -2
grep -aE "snapshot .* saved|done \(rc=|failed" /var/log/restic-backup.log | tail -3
```

`rc=0` everywhere = fine. Any `failed`/`FAILED` line names the culprit
(instance, database or path). All scripts exit non-zero on any error,
never silently.

## Restoring

- **A whole instance, fast (same box)**: `incus copy backup:<inst>`
  style — copy the replica from project `backup` back into `default`
  ([ks4/incus-copy.md](ks4/incus-copy.md)); from nuc the same via the
  remote.
- **A file or directory** (any date within retention):
  `restic -r s3:s3.sbg.io.cloud.ovh.net/restic-data restore <snapshot> --target /backup/restore-x --include <path>`
  (never restore into `/tmp` — it is RAM). Env: `. /root/.restic-env`.
- **A database**: restore the `.sql` dump from `restic-data`
  (`/backup/dumps/mariadb/<inst>/<db>.sql`, `grants.sql` for users), load
  it with `incus exec <inst> -- mariadb < dump.sql`.
- **An instance when no replica survives** (worst case: ks4 and the
  replica sites are gone): recreate the container from its page in
  [ks4/](ks4/) (the doc *is* the install script), restore its data
  trees and database dumps from `restic-data`, and use the incus
  configuration captured nightly in the dump tree
  (`/backup/dumps/incus/incus-global-db.sql`) to check devices,
  profiles and addresses.

Secrets you need for any of this: `/root/.restic-passphrase` and the S3
keys in `/root/.restic-env` — **both are in the password manager**;
without the passphrase the S3 buckets are unreadable.

## Adding something to the backups

New instances are picked up automatically by the replica and
instance legs (all instances, opt-out only). Databases are
auto-discovered. Only **data trees** need one line in
[`restic-paths`](https://git.lutran.fr/julien/scripts/src/branch/main/restic-paths) — see [new-container.md](new-container.md).