tenant-engine/workplans/TEN-WP-0009-postgres-production-store.md

---
id: TEN-WP-0009
type: workplan
title: "PostgreSQL as the production store, SQLite for dev and test"
domain: infotech
repo: tenant-engine
status: ready
owner: claude
topic_slug: tenant-lifecycle
created: "2026-08-16"
updated: "2026-08-16"
depends_on:
  - TEN-WP-0007
unblocks:
  - TEN-WP-0008
---

# TEN-WP-0009 - PostgreSQL production store

Move the production store from SQLite-on-a-PVC to the fleet's CloudNativePG
infrastructure. SQLite stays, deliberately, as the dev and test backend.

## Why this reverses an earlier decision

TEN-WP-0005-T02 chose SQLite over PostgreSQL on purpose, and the reasoning was
sound at the time: TEN-WP-0004 had shipped SQLite on a PVC, so *"adding an
unused Postgres path would have been dead code"*. The `TenantStore` Protocol
was kept precisely as the seam for this change.

Three things have changed since:

1. **The PVC is now blocking work.** The volume is `ReadWriteOnce`, which forces
   `strategy: Recreate` and makes a side-by-side canary impossible — the
   constraint TEN-WP-0008-T02 ran into when onboarding to staged promotion. The
   store choice is no longer invisible to anything outside this repo.
2. **The infrastructure is already there and already proven.** The
   CloudNativePG operator runs on railiance01 with seven clusters, and
   `user-engine` — our sibling service, sharing the `tenant_id` key — has run
   its own `user-engine-pg` for 19 days.
3. **A Postgres path is no longer unused.** It becomes the production path, so
   the dead-code objection no longer applies.

SQLite is *not* being removed. It stays as the dev and test backend, where a
zero-setup file-backed store is genuinely the right tool, and it keeps the
conformance suite honest by forcing the Protocol to stay a real seam rather
than a formality wrapped around one implementation.

## Credential handling

CloudNativePG mints the connection secret itself: a cluster named `X` produces
secret `X-app` with key `uri`. The Deployment references it via
`secretKeyRef`, exactly as `user-engine` does with
`USER_ENGINE_DATABASE_URL` ← `user-engine-pg-app/uri`.

So **no secret enters this repo, this workplan, or any evidence dump**, and no
`warden route` lookup is needed — this is not a credential we fetch, custody,
or rotate. Runtime secret custody remains OpenBao's per `SCOPE.md`; an
operator-minted in-cluster secret is outside that lane.

## T01 - Decide the topology and write the cluster manifest

```task
id: TEN-WP-0009-T01
status: todo
priority: high
```

Decide between a dedicated `tenant-engine-pg` cluster in our namespace and
sharing an existing one (`net-kingdom-pg` or `apps-pg` in `databases`).

Argue it rather than defaulting. Points to weigh: `user-engine` chose dedicated
and is the closest precedent; a dedicated cluster keeps blast radius and backup
policy per-service; a shared cluster is cheaper on a single node and
`net-kingdom-pg` already exists for this product family. Note that
`tenant-engine` is consulted by `flex-auth` on the authorization path, so its
availability envelope is not purely its own.

Write the CNPG `Cluster` manifest into `deploy/`, matching the fleet's existing
image and storage conventions rather than inventing new ones.

Also decide **backups**. The `scheduledbackups.postgresql.cnpg.io` CRD is
available; SQLite-on-a-PVC had no backup story at all, so this is a gain to
claim explicitly rather than inherit by accident.

Done when the topology decision is recorded with its reasoning and the manifest
is committed.

## T02 - Implement `PostgresTenantStore`

```task
id: TEN-WP-0009-T02
status: todo
priority: high
```

Implement the full `TenantStore` Protocol — including
`guardrail_overrides` / `guardrail_changes` / `set_guardrail_override` from
TEN-WP-0006 — and add PostgreSQL to the conformance suites, which are already
parametrised over in-memory and SQLite. A third backend should be a fixture
parameter, not a new test file.

Invariants that must hold identically, not approximately:

- `mutate_tenant()` commits idempotency replay, version CAS, mutation, and
  audit event **in one transaction**;
- `set_guardrail_override()` does the same for the override, its audit record,
  and its receipt;
- a replayed `Idempotency-Key` short-circuits *before* the version check;
- reads and writes never observe a row mid-transaction.

That last one is where PostgreSQL should simplify rather than complicate:
SQLite needed an explicit `RLock` around reads because one connection is shared
across request threads, and the concurrent-writer test caught a real defect
there. Postgres gives proper per-connection transaction isolation, so the lock
should disappear rather than be ported. **Do not transliterate the SQLite
implementation** — port the semantics and let the backend do what it is good
at. Use a connection pool and appropriate isolation, and prove the guarantees
with the same concurrent-writer test that caught the SQLite bug.

Adds a runtime dependency (`psycopg`); keep it out of the base install path if
SQLite-only dev is meant to stay dependency-light.

Done when all three backends pass the same conformance suites unchanged.

## T03 - Backend selection that fails closed

```task
id: TEN-WP-0009-T03
status: todo
priority: high
```

`Settings` currently carries only `database_path`. Add a database URL and make
selection explicit:

- URL set → PostgreSQL;
- path set → SQLite;
- **both set → refuse to start.** Do not silently prefer one. An ambiguous
  store configuration in production is exactly the class of silent
  misconfiguration this repo fails closed on everywhere else, and picking a
  winner would let a stale `TENANT_ENGINE_DATABASE_PATH` quietly shadow the
  real database;
- neither set → in-memory, as today, which is correct for tests and wrong for
  production.

Consider surfacing the active backend on `/health`. The last two production
incidents were invisible because the service looked fine from outside; "which
store am I actually using" is cheap to answer and expensive to guess.

Done when misconfiguration is a startup failure with a clear message, covered
by tests.

## T04 - Migrate production data

```task
id: TEN-WP-0009-T04
status: todo
priority: high
```

Move the live SQLite database to PostgreSQL. Currently small — two tenants
(`tenant:trial:portalcheck` active v1, `tenant:trial:ten-wp-0005-t05` retired
v5) plus the T04 disposables from TEN-WP-0007 — but small is not the same as
trivial.

Everything must move, not just the tenants:

- `tenants` with versions and lifecycle timestamps **preserved exactly** — a
  reset version silently breaks every consumer holding an ETag;
- `grants` including revoked ones, because the trail is append-only and its
  history is the audit record;
- `plans`;
- `events` — the audit correlation contract;
- `idempotency_receipts` — dropping these lets an in-flight retry double-apply
  a mutation that already happened;
- `guardrail_overrides` and `guardrail_changes`.

SQLite is single-writer and the app writes to it, so the cutover must stop
writes rather than race them: scale to zero, export, import, verify, then start
against PostgreSQL. Verify by comparing row counts *and* spot-checking the two
known tenants' versions and lifecycle state, not by trusting the exporter.

Keep the SQLite file and its PVC until T05's soak passes. It is the rollback.

Done when a verified copy is live in PostgreSQL and the comparison evidence is
recorded here.

## T05 - Cut over the deployment

```task
id: TEN-WP-0009-T05
status: todo
priority: high
```

Update `deploy/tenant-engine.yaml`:

- drop the PVC and its volume mount;
- add `TENANT_ENGINE_DATABASE_URL` from the CNPG-minted `secretKeyRef`;
- switch `strategy: Recreate` → `RollingUpdate`, now that no `ReadWriteOnce`
  volume forces serialization — **this is what unblocks TEN-WP-0008-T02's
  canary**;
- extend the `NetworkPolicy` egress to the Postgres service, and no wider.
  Ingress stays restricted to `user-engine`.

Then decide, deliberately, whether to raise `replicas` above 1. It becomes
possible here for the first time; possible is not the same as warranted, and a
second replica changes failure modes for a service on the authorization path.

Update `make verify-pin` if the expected shape changes, and re-run it.

Rollback: re-pin the previous digest and re-attach the PVC. State plainly that
this becomes lossy once writes have landed in PostgreSQL — after that point the
rollback is "restore from Postgres", not "swap back to the file".

Done when production runs on PostgreSQL, `make verify-pin` passes, and the
TEN-WP-0007 T04 verification list still passes end to end against the live
service.

## T06 - Tell the fleet, and close the loop on TEN-WP-0008

```task
id: TEN-WP-0009-T06
status: todo
priority: medium
```

- `flex-auth`: availability characteristics of their data source changed. No
  contract or action change.
- `user-engine`: no contract change either, but they run the same CNPG pattern
  and may have operational lessons worth having before we repeat their mistakes.
- **TEN-WP-0008-T02**: record that the `ReadWriteOnce` canary constraint is
  gone, so staged-promotion onboarding no longer has to describe a canary that
  cannot run.

Done when the notes are sent and TEN-WP-0008-T02 is updated.

## Out of scope

- **Removing SQLite.** It stays as the dev and test backend, and as the thing
  that keeps `TenantStore` an honest seam.
- **Schema redesign.** Port the existing schema; a store migration and a model
  change at the same time makes any regression ambiguous.
- **Sharing a database with `user-engine`.** `tenant_id` is the only key the
  two services share, and it stays that way — separate stores are the boundary,
  not an implementation detail.