# Off-host backup & restore

HealthLog ships with an optional daily off-host backup that ships every
user's JSON dump, encrypted with AES-256-GCM under a SEPARATE key
(`BACKUP_ENCRYPTION_KEY`), to any S3-compatible bucket — Cloudflare R2,
AWS S3, Backblaze B2, MinIO, etc.

These per-account copies roll one account back on the same server. To
rebuild a server, use the nightly database dump, which the same job
configuration also uploads (`database/healthlog-<time>-daily.dump.enc`, in the
envelope below): [`disaster-recovery.md`](disaster-recovery.md).

The backup runs at **02:30 Europe/Berlin** every day from the worker
container (queue `data-backup-offhost`). Object key layout:

```
<bucket>/YYYY-MM-DD/user-<userId>.json.enc
```

## Wire format (binary)

```
magic   = "HLBK"           (4 bytes, ASCII)
version = 0x04             (1 byte)
keyIdLen, keyId            (1 byte + 12 ASCII hex: the first 12 hex digits of SHA-256(key))
iv      = 12 random bytes  (AES-GCM nonce)
ciphertext = N bytes       (AES-256-GCM over gzip(JSON dump), key = BACKUP_ENCRYPTION_KEY,
                            associated data = "healthlog/offhost-backup/v4|<object key>")
authTag = 16 bytes         (AES-GCM tag, trailing)
```

Version `0x04` (from v1.39.3) adds two things. The key id says which off-host
key an object needs, so a reader holding a retired key as well finds the right
one. The associated data is the object's own key in the bucket,
`YYYY-MM-DD/user-<id>.json.enc`: an object copied to another account's name or
another date does not decrypt, where before it opened as if it belonged there.
The restore script passes the key it downloaded, so nothing changes for an
operator.

Four versions exist in the wild and all four restore. `0x01` encrypted the
JSON directly and `0x02` gzipped it first; both carry the tag in FRONT of the
ciphertext, which is what made them impossible to write a piece at a time —
GCM only produces the tag once the last block is in, so a leading tag means the
whole object has to exist before its first byte can be sent. `0x03` moves the tag to the end and changes nothing else: it still
covers every ciphertext byte, and the reader still verifies it before returning
a single byte of plaintext. Objects already in your bucket stay readable, and
the restore script needs no flag to tell them apart.

## Required env vars

| Var                               | Required | Notes                                                                               |
| --------------------------------- | -------- | ----------------------------------------------------------------------------------- |
| `BACKUP_ENCRYPTION_KEY`           | yes      | 64 hex chars or 32-byte base64. **Different from `ENCRYPTION_KEY`.**                |
| `BACKUP_S3_ENDPOINT`              | yes      | e.g. `https://<account>.r2.cloudflarestorage.com`                                   |
| `BACKUP_S3_BUCKET`                | yes      |                                                                                     |
| `BACKUP_S3_ACCESS_KEY`            | yes      |                                                                                     |
| `BACKUP_S3_SECRET_KEY`            | yes      |                                                                                     |
| `BACKUP_S3_REGION`                | no       | defaults to `auto` (Cloudflare R2)                                                  |
| `BACKUP_RETENTION_DAYS`           | no       | not read by the app; the number for your bucket's lifecycle rule                    |
| `BACKUP_ENCRYPTION_PREVIOUS_KEYS` | no       | retired off-host keys, comma-separated, read only (see "Rotating the off-host key") |

## Bucket permissions

The worker needs `PutObject`, `GetObject`, `ListBucket`, `DeleteObject` and
`AbortMultipartUpload`. On Cloudflare R2 the **Object Read & Write** token
covers all of them.

`DeleteObject` is needed because the app deletes objects in two cases, and
only those:

- **An account is deleted, or its data is wiped.** Deleting an account,
  deleting a managed profile and "Delete all data" each write a deletion
  request in the same transaction as the deletion. The `offhost-backup-purge` job lists the bucket, deletes every
  `YYYY-MM-DD/user-<id>.json.enc` of that account and removes the request once
  nothing of the account is left. It runs right after the deletion and again
  every night at 03:40. A copy the nightly upload was writing while the account
  was deleted is removed by the upload itself.
- **The connection test** deletes its own `_healthcheck/<ts>.bin`.

The database dumps are not purged per account. A dump is the whole database
at one moment, so an account deleted since stays in the dumps taken before
its deletion until they age out: after `DB_BACKUP_KEEP` nights on the server,
and in the bucket after the lifecycle rule for `database/`. That is backup
retention, and the period to state to the people using your instance; the
backups page shows both numbers and warns when no rule covers `database/`
([`disaster-recovery.md`](disaster-recovery.md)).

The admin wipe of every account deletes nothing in the bucket. It is you
clearing your own host, the bucket is yours, and its copies are the way back
from a wipe pressed by mistake. If you are handing the host on, empty the
bucket yourself.

Earlier versions of this page said the worker never deletes an object. That
was the design until v1.39.3, and it meant a deleted account's copies stayed
in the bucket for as long as the lifecycle rule kept them, or forever without
one. If the bucket refuses the delete (a credential without `DeleteObject`),
the request stays, the job retries it every night, and **Admin → Backups →
Off-host** shows how many deletions are outstanding and the bucket's answer.

`AbortMultipartUpload` only reaches an upload the same worker started and is
what clears the parts of a run that failed halfway. Without it, a failed
upload leaves parts that are billed and do not show in a bucket listing.

## Bucket lifecycle (required for retention)

The app does not expire objects by age, and nothing in the app reads
`BACKUP_RETENTION_DAYS`. Expiry is the storage provider's lifecycle rule, set
to match the number you wrote there. Without one, every nightly copy of every
account is kept forever. **Admin → Backups → Off-host** reads the bucket's
lifecycle configuration and says so when there is none, or when the credential
may not read it (grant `GetLifecycleConfiguration` to let it check):

```
Filter: "" (all objects)
Action: Expire after 30 days
```

For Cloudflare R2 add this from the bucket's **Settings → Lifecycle**.

## Smoke test

After deploying, hit `POST /api/admin/backup/test` (admin-only). It
performs a 1-byte PUT + GET round-trip and returns:

```json
{
  "data": {
    "endpoint": "https://...r2.cloudflarestorage.com",
    "bucket": "healthlog-backups",
    "region": "auto",
    "putLatencyMs": 142,
    "getLatencyMs": 38,
    "ok": true
  },
  "error": null
}
```

The credentials are never returned.

## Restore

Pick a key (e.g. `2026-05-08/user-clx123.json.enc`) from the bucket
and run the restore script with the same backup credentials and
encryption key the backup was written under — a freshly generated
`BACKUP_ENCRYPTION_KEY` cannot decrypt any existing object:

```bash
BACKUP_S3_ENDPOINT=https://...r2.cloudflarestorage.com       \
BACKUP_S3_BUCKET=healthlog-backups                           \
BACKUP_S3_ACCESS_KEY=...                                     \
BACKUP_S3_SECRET_KEY=...                                     \
BACKUP_S3_REGION=auto                                        \
BACKUP_ENCRYPTION_KEY=<the key the backup was written under> \
pnpm dlx tsx scripts/restore-backup.ts \
  2026-05-08/user-clx123.json.enc \
  /tmp/restored.json
```

Run this command from a source checkout with the production backup variables
exported. The script imports the full application dependency graph, which the
minimal production image does not expose as an operator scripting environment.

The script downloads the object, decrypts it, and writes the JSON dump
to disk. Importing the JSON back into a HealthLog instance is left to
the operator (use `prisma db seed` or a custom script).

Restoring is not streamed and does not need to be. It holds the whole document,
because the next thing anyone does with a backup is parse it as one JSON
object, and handing back plaintext the auth tag has not yet covered would trade
the authentication for memory. It runs on your machine rather than in the
container, so give it room: a record of several hundred thousand measurements
decompresses to a few hundred megabytes, and
`NODE_OPTIONS=--max-old-space-size=2048` in front of the command is enough for
a 445 000-measurement account.

### Restoring from the backups console

An admin can restore a stored snapshot from the browser instead of the shell.
`/admin/backups` lists one row per account and per backup type: **Backup now**
enqueues the `data-backup` pass for every account on the instance, **Download**
decrypts one snapshot and hands back the JSON, and **Restore** opens a dialog
that first shows what the file carries and then requires the word `RESTORE` to
be typed before it will run. The restore targets the account the snapshot was
taken for, never the admin running it, and it refuses a file whose declared
owner does not match the stored row. Instance-wide settings ride along only
when you tick _Also restore instance settings_ in the dialog; leave it clear to
restore the account alone.

A stored copy this instance can no longer open — the key that wrote it dropped
from `ENCRYPTION_KEYS` one rotation too early, or bytes that are not the ones
written — is refused by all three buttons with `422` and
`meta.errorCode = backup.payload.undecryptable`, before anything is read back.

### What a backup deliberately does not carry

Every credential-shaped row is left out, and this is not an oversight to fix:
API tokens, trusted devices, step-up elevations, known devices, clinician share
links, and the account grants behind shared record access. Restoring data is
rolling a record back to a known state. Restoring an authorization is different
in kind, because a grant the owner revoked on Tuesday would come back alive out
of Monday's file with nobody deciding it and neither person told.

What this means in practice depends on where you restore to.

**Onto the same instance.** Nothing changes. The restore replaces the account's
data tables and does not touch grants, tokens or devices, so shared access
carries on exactly as it was. Somebody who had read access before the restore
still has it afterwards, now looking at the restored data.

**Onto a fresh instance.** None of it comes with the file. Nobody has access to
anybody's record, every API token has to be reissued, every device re-trusted,
and both people have to invite and accept again before sharing works. That is
the fail-safe direction — access lost, never access resumed — and re-consenting
is the right amount of ceremony for handing someone your health record a second
time. Plan for it rather than discovering it.

The full per-model reasoning lives in `src/lib/export/backup-plan.ts`, where
every excluded model carries a written verdict and a structural test refuses to
let a new model land without one.

## Container memory (the nightly off-host job)

This is the part that bites, and it bit the nightly job a release after it bit
the weekly one. The job runs inside the app process, so V8's heap limit is the
app's heap limit. Node sizes it from the container's memory cap: 1 GB gives a
524 MB old-space limit, the compose default of 1536m (since 1.40.1) gives 792 MB. A long-lived Next.js server is already holding a large share
of that before the job starts.

The uploader used to build the whole backup JSON as one string, gzipped
that whole string, ran a whole-buffer cipher pass over the result and handed
the finished buffer to a single `PutObject` — four full copies of the record
alive at once. On an account of 445 000 measurements the JSON alone is 242 MB,
and the first configured run took the container down seventeen seconds in with
`FATAL ERROR: Reached heap limit`. Because the job shares the app process, one
account's size restarted the instance for everybody on it.

It streams now. The JSON is produced a page at a time, gzip and the cipher
consume it as it arrives, and the object goes up as a multipart upload that
holds two 8 MB parts. What the process holds is fixed by that pipeline's shape
rather than by the size of the record going through it: measured on the same
445 000-measurement account under `--max-old-space-size=450`, the old path
died and the new one finished holding tens of megabytes, writing a 9.1 MB
object that restores to the identical record.

Up to 1.43.4 that held for the tables that are long in rows, not for the
ones that are heavy in bytes. The stored documents and the ECG traces were
still read whole, and a vault of 190 MB cost about five times that in heap:
the bytes, their base64, the section's JSON and the preview's copies of each
row. A single account with that many documents took a 524 MB process down on
every weekly run, while 1.25 million measurements beside them fitted easily.
Both writers now read the traces a page at a time and the documents one at a
time, each document's bytes in slices of 1.5 MB. Measured on that account
under `--max-old-space-size=524`, the peak went from 930 MB (a crash) to
209 MB. The restore had the same problem in the other direction: it kept
every document of the file in memory and peaked at 1.25 GB on the same copy.
It now leaves the stored bytes out of its first read and writes the
documents one at a time from a second one, and the copy restores every
document byte for byte inside the 524 MB heap.

One ceiling remains, and it is structural rather than a memory bound: a
multipart upload carries 10 000 parts, so 80 GB is the largest object one
account can produce. Past it the account's backup fails with a clear refusal,
is counted in the run's `offhost_backup_oversized` meta, and the pass carries
on with everybody else.

### Reading a failed run

A nightly run that could not upload for **anybody** now fails the pg-boss job
instead of reporting success. This is the case wrong credentials, a missing
bucket and an unreachable endpoint all land in, and the target's own sentence
rides out as the failure cause — `The request signature we calculated does not
match the signature you provided`, `The specified bucket does not exist`,
`connect ECONNREFUSED`. Check `offhost_backup_uploaded` against
`offhost_backup_total_users`: before this change a run where every single
upload failed still read `ok: true`, so a bucket could stay empty while the
jobs page looked healthy.

A run where SOME account got a copy still succeeds, with the rest counted in
`offhost_backup_failed`. Failing the whole queue over one account's object
would re-upload everybody's on every retry.

### A run the process died under

Both backup jobs carry a pg-boss heartbeat of five minutes. While a run is
alive the worker refreshes it; a run whose process died (a restart, or a
container killed for memory) stops refreshing, and pg-boss fails the job with
`job heartbeat timeout` within minutes instead of leaving it `active` until its
two- or four-hour expiry. The retries the queue already allows then pick it up.

Each pass also notes when it started and when it got past every account
(`backup_pass_attempts`). An account whose last attempt started and never
finished is the one the process died under, and the next run takes it last, so
one record too large for the container cannot keep every account after it from
a copy. **Admin console → Backups** shows when the run in progress started and
names such an account under both the weekly and the off-host card. Seeing the
same account there twice means it needs more memory than the container has.

### Which account has no copy

The counts above say how many accounts were uploaded, never which. An account
whose object has failed every night for a month reads as `99 uploaded, 1
failed` each time, which looks like weather.

**Admin console → Backups → Off-host copies** answers it per account: when this
host last put that account's encrypted copy in the bucket, how big it was, and
how that compares with the nightly schedule. **Fresh** is inside one run,
**due** means one run produced nothing for that account, **stale** means two
did not, **never** means a run walked the account and no object has ever
landed for it, and **no record yet** means no run has recorded the account at
all. On a host without `BACKUP_S3_*` the card says off-host backup is not
configured and stops there.

The ledger starts empty on the release that adds it, so on a host that has
been uploading nightly for months every account reads **no record yet** until
the first run after the upgrade. That is the ledger having no history, not the
bucket being empty — which is why it is a separate word from **never**, and
why the row says so rather than claiming nothing has ever reached the bucket.

Each verdict carries six hours of slack on top of the schedule's own 24, and
that slack is load-bearing on two nights. The cron runs at 02:30 Europe/Berlin,
so on the DST fall-back Sunday two consecutive runs are 25 hours apart; and the
timestamp is when _that account's_ object landed, so on a cohort walked one
account at a time an account reached later tonight than last night drifts by
hours. Without the slack a healthy host would paint its whole cohort **due**
once a year.

The verdicts come from a ledger the worker writes when the object lands
(`offhost_backup_state`), not from a listing of the bucket. Keep the worker's
grant as documented — PutObject, GetObject, AbortMultipartUpload — and the card
still tells the truth. A row that goes stale while the run reports success is
that account's object being refused, and the reason is in the run's
`offhost_backup_failures` meta.

## The weekly in-database backup (`data-backup`)

Separate from the off-host job above, and easy to confuse with it. A second
pg-boss job writes one `WEEKLY_AUTO` copy per user into the database, the same
JSON document, gzipped and then encrypted under `ENCRYPTION_KEY` /
`ENCRYPTION_KEYS`, staying inside the instance. It is what
`/api/admin/backups/<id>/restore` reads, and an uploaded backup file is stored
the same way.

### How a copy is stored

From v1.39.2 a copy is kept as ordered pieces of about a megabyte in
`data_backup_chunks`, with the list of pieces on its `data_backups` row. The
writer produces the JSON a page at a time, gzips it as it goes and seals each
megabyte of gzip output on its own with AES-256-GCM. Reading it back (restore,
preview, download) takes the pieces one at a time. Nothing on either path holds
the whole copy, so the size of a copy has nothing to do with the app's memory.
Measured on an account of 2.6 million readings in a 1 GB container,
with the web server and the worker in one process: the backup took 87 seconds
and stored 97 MB in 96 pieces, the preview 20 seconds, the download of the
1.4 GB file 25 seconds, and the restore 264 seconds, which gave back every
reading exactly. The container peaked at 567 MB and did not restart. What the
backup, preview and download hold on top of the running app stays at a few tens
of megabytes and does not grow with the account. A 512 MB container is too
small for the app itself: its heap limit is 259 MB and a backup of any account,
even one with 130 000 readings, runs it out of heap.

Each piece carries, inside its encryption, which copy it belongs to, its
position, and whether it is the last. Before a restore deletes anything, every
piece is checked: a piece that is missing, moved, altered, taken from another
copy, or a copy that stops short of its last piece is refused with
`backup.payload.undecryptable`, and the account is left as it was.

The write is one transaction. Until the new copy is complete the previous one
stays in place and readable; a run that fails halfway leaves it untouched. A
second backup of the same account started while one is running (a manual run
during the weekly one, say) waits for the first to finish and then replaces
its copy; neither leaves a partial copy behind.

While a restore of an account's copy is queued or running, the weekly and
manual backup leave that account's copy alone and back up everyone else. The
run's `users_skipped_restoring` meta counts such accounts; the next run
replaces the copy as usual. If a copy is replaced anyway while it is being
read (a download or preview in progress when the weekly run finishes), the
reader answers `409` with `backup_changed` and "The backup was replaced by a
newer one while it was being read", not the undecryptable error, and a restore
rolls back with nothing changed. Start it again to use the new copy. A
download already sending when this happens stops partway; download again.

Copies written before v1.39.2 are a single value in `data_backups.data` and
still restore, preview and download as they did. The next weekly run replaces
the weekly copy in the new form, and a key rotation (below) converts every
remaining one, including uploaded copies. Until then those older copies are
read as one value, as before, which needs the memory they needed when they were
written.

Migration 0352 cannot be undone by going back to v1.39.1. That release reads
only the single value, so it finds a copy in pieces empty, and if it writes a
weekly copy into a row that has pieces, the row holds both forms. v1.39.2 then
refuses to read that row, because nothing says which of the two is current
("This backup holds both a single stored value and pieces ..."); the next
weekly backup replaces it. If you must go back, restore the database backup
you took before upgrading.

### The size limit

The one limit left is on storage: a copy of one account may take at most
`BACKUP_MAX_STORED_MB` megabytes (default 2048). It exists so a runaway copy
fails with a message instead of filling the database volume, which holds the
old and the new copy side by side while a backup runs. An account past it fails
for that account alone, is counted in the run's `users_failed` and
`records_oversized` meta, and keeps its previous copy; the pass carries on with
everybody else. The message names the setting. Raise it in `.env`, recreate the
app container, and make sure the database volume has room for two copies of
that size.

Before v1.39.2 the limit was a fifth of the app's heap, 105 MB in a 1 GB
container, because the copy had to pass through the app as one value. An
account with 1.75 million readings was past it, and the only way round was more
memory. That is no longer the case: `records_oversized` means the storage limit,
never memory.

The writer deliberately reads no heap gauge. A version that did shipped in
v1.38.6 and compared the whole process's live usage, garbage included, against
80 % of the limit. A Next.js server that has been up for a week sits at 400 MB
of largely collectable heap, so the weekly pass aborted every account on the
first chunk, including one whose whole stored copy is 1.2 MB, and reported
success while doing it. If you are on v1.38.6, a `data-backup` run that finishes
in seconds having backed up nothing is that defect and not your record.

### Key rotation

Rotation reaches a stored backup's envelope and nothing inside it. The
content of a disaster-recovery backup is the database's ciphertext, carried
as it is stored, and a restore writes it back verbatim: a note, a document or
a coach message inside a copy taken before a rotation still needs the key the
rotation retired. The same holds for every copy in the off-host bucket and for
every file an operator has downloaded. So the rule is: **keep a retired
`ENCRYPTION_KEYS` entry until no backup you may still restore needs it.**
**Admin → Encryption → Keys the backups still need** lists, per key id, the
stored copies that need it with the oldest date, and when the last off-host
copy needing it expires under the bucket's lifecycle rule. Copies written
before v1.39.3 did not record their keys and are listed as such.

Every restore, the restore preview, the admin upload and the monthly drill
check this before anything is changed: a file whose content needs a key this
server does not have (or an id whose key material differs) is refused with the
key id named, and the account is left as it was.

Re-encrypting the content of stored backups during rotation was considered and
not done: it would mean decrypting, parsing, re-encrypting and re-writing every
copy in full, and it still could not reach the off-host copies or downloaded
files, so the rule above would be needed regardless.

`scripts/rotate-encryption-key.ts` and the rotation in the admin console
re-seal every piece under the active key, in small batches, without reading
the backup inside. The link between a piece, its copy and its position is
inside the encryption, so it comes through rotation unchanged.

A copy still in the older single-value form (any of them, including the
`~hlgcm1.` form v1.38.6 to v1.39.1 wrote) is not re-sealed in place, which would need the
whole copy in memory several times over. Rotation converts it into pieces
under the active key instead, one copy at a time, reading the stored value a
few megabytes at a time; the copy keeps its date. The conversion of a copy is
one transaction, so a copy that fails its check is left exactly as it was and
counted as an error. Rotation up to v1.39.1 counted every `~hlgcm1.` copy
as an error; run it again after updating before retiring the old key.

### What a restore replaces

A restore replaces the account's data tables; it does not merge into them.
Every row the file carries is written back under its original id, and every row
the account gained after the snapshot was taken — readings, doses, mood
entries, documents — is deleted with the rest of the class before the file is
read back. Restoring Monday's copy on Wednesday therefore costs the account
everything it recorded on Tuesday. If the current state is worth keeping, take
a fresh snapshot from the backups console before restoring the old one.

## Rotating the off-host key

`BACKUP_ENCRYPTION_KEY` is the key new objects are written under. To rotate
it, set the new key there and move the old one into
`BACKUP_ENCRYPTION_PREVIOUS_KEYS` (comma-separated if there are several), then
restart. New objects are written under the new key; older objects stay
readable because every version-4 object names its key and older objects are
tried against each key in turn. Remove the old key once the lifecycle rule has
retired every object written under it, that is `BACKUP_RETENTION_DAYS` after
the restart.

## Monthly restore drill (automatic)

Since v1.16.4 a pg-boss job (`data-restore-drill`, cron `11 4 1 * *` —
04:11 on the 1st of each month) exercises the read path end-to-end:
fetch every backup object of the most recent date from the bucket (one per
account), decrypt each under the current `BACKUP_ENCRYPTION_KEY`, JSON-parse
it, and sanity-check the payload shape. It performs **no database restore** —
it validates the artefacts, not the import path. Each account is checked and
reported on its own: one object that fails is named, and the others are still
read.

Outcomes:

- **Success** — record counts, object age, and sizes land in the
  wide-event meta (`job.restore_drill`).
- **Stale chain** — the newest object is older than 3 days: the nightly
  uploader has stalled (or the lifecycle rule is too aggressive). The
  drill pages via the worker error reporter (stderr + GlitchTip).
- **Failure** — empty bucket, fetch error, decryption failure (wrong or
  rotated key), malformed JSON: pages the same way, once per failing object,
  with the object key and how many accounts were checked. A decryption
  failure right after a `BACKUP_ENCRYPTION_KEY` change means the new
  key cannot read the existing objects: put the old key into
  `BACKUP_ENCRYPTION_PREVIOUS_KEYS` (see "Rotating the off-host key").
- **Content under a missing application key** — the object opens, but its
  content was written under an `ENCRYPTION_KEYS` entry this server no longer
  has, or under an id whose key material changed. The drill decrypts the
  shortest value of each section under every key id it finds, and pages naming
  the key when none of them opens. A restore of that object
  would write back rows nobody can open; put the key back before restoring.
- **Not configured** — deployments without the `BACKUP_S3_*` vars skip
  silently (wide-event warning only).

The drill lists the bucket to find the newest object, so it needs
`ListBucket` on top of the uploader's `PutObject`, `GetObject` and
`AbortMultipartUpload`. Cloudflare R2's **Object Read & Write** token covers
all four.