felhom.eu/documentation/architecture/05-hub-architecture.md

# Architecture Part 5 — The Hub

> Status: design draft (decision content). To be validated by Claude Code against the **actual
> felhom-hub source** (`felhom.eu` repo, `hub/`) + Parts 01–04, then placed at
> `docs/architecture/05-hub-architecture.md`.
>
> The hub is **not** greenfield — it's a mature service (felhom-hub v0.6.3, Go + SQLite on k3s,
> `hub.felhom.eu`). This doc is the **deltas** to evolve it for the Proxmox model, plus the new
> data model. Builds on Part 1 (trust/enrollment), Part 3 (the agent + reconcile), Part 4 (signing).

## 1. Source-of-truth model — two drivers, two directions

The single most important framing, and the one that governs everything below: the hub is **not** a
monolithic source of truth. State flows in two directions with opposite drivers.

- **Operator-driven *intent* — hub authors, agent reconciles (top-down).** Which guests should
  exist and their spec, storage *policy* (a target's role/class/backup schedule), controller +
  golden-image versions, identity, tunnel. The operator sets these in the hub; the agent converges
  toward them. Here the hub *is* the source of truth.
- **Box/customer-driven *reality* — box authors, pushes up, hub mirrors (bottom-up).** Which USB
  drive is *physically* attached (and its `durable_id`), what apps are deployed and where, the
  customer's controller configs/settings, host/guest health, latest PBS snapshot pointers. The
  customer or the physical world drives these; the box reports them; the hub stays an up-to-date
  **mirror** but is **never** the driver.

They meet at a **handshake**, not a tug-of-war. Storage is the clearest case: the customer plugs in
a drive → the agent *detects* it and reports `durable_id X attached` (reality) → the operator
assigns `role=bulk, class=slow, backup=weekly` (policy, intent) → the agent reconciles that policy
*onto the detected drive*. **Apps never enter the reconcile loop** — app deployment is the
controller's domain (customer- or operator-driven, inside the guest); the hub only mirrors the
resulting inventory. **Reconciliation applies to infrastructure; the app/customer layer is mirrored.**

## 2. Data model (Part 1 decision (b): customer-anchored)

A customer's deployment is one **Host** (its agent) plus one-or-more **Guests** (its controllers).
1 customer = 1 host + N guests; the shared-host multi-tenant case is deferred (not precluded — the
`hosts` table is the seam it would use).

- **`customer_configs`** (existing) — the Customer anchor: identity, domain, email,
  `retrieval_password`, status, config_json. Unchanged role.
- **`hosts`** (new) — `host_id PK, customer_id, api_key` (the agent's hub key), `agent_version`,
  desired-state intent (storage manifest + policies + golden-image version, as JSON), a per-host
  **`desired_generation`** counter, the slim DR record (§9), timestamps.
- **`guests`** (new) — `guest_id PK, customer_id, host_id, api_key` (the controller's hub key),
  `display_name, controller_version`, per-guest **`desired_spec_json`** (CPU/mem/disk, versions),
  timestamps.

**Per-reporter keys:** today's per-customer `customer_configs.api_key` becomes per-reporter —
`hosts.api_key` (agent) and `guests.api_key` (controller). The hub resolves a presented Bearer key →
host or guest → customer; `customer_configs.api_key` goes unused once auth resolves via the new keys.
**Clean cutover:** no dual-model support; the demo re-enrolls fresh into `host + guests`.

## 3. Report ingest — two domains

The single controller report splits. The de-privileged controller no longer sees host disks/storage/
backup, so its report **slims** (it loses System/Storage/Backup, keeps app-domain).

- **`POST /api/v1/host-report`** (new, agent) → **`host_reports`**: host CPU/RAM/disk, per-guest
  up/down + spec, storage-target status (attached drives + `durable_id` + reachability), last backup
  + restore-test per target, latest PBS snapshot pointers, `cloudflared` health, agent + controller
  versions. Denormalized columns for the dashboard; full `report_json`. Index `(host_id, received_at
  DESC)` + `(customer_id, received_at DESC)`.
- **`POST /api/v1/report`** (existing, slimmed controller) → the renamed **`guest_reports`**: it
  gains `guest_id` + `host_id`; its `cpu/memory` denorm now means *guest-level*; `backup_last_snapshot`
  goes quiet (backup status lives in `host_reports`). App telemetry / log issues stay.

These two streams are the bottom-up mirror of §1 — they keep the hub current without a separate push.

## 4. Liveness / dead-man's-switch

Evolves the existing staleness checker (60s **cadence**, 30m/1h **thresholds** — OK <30m, down at
2× = >1h; today: controller-report recency → `node_stale`/`down`/`recovered`):

- **Primary = host-report recency → `host_stale` / `host_down`.** The agent heartbeat is the box's
  liveness signal; a silent agent = the box is gone (the critical alert).
- **Guest up/down comes from the host report's per-guest status** — authoritative, every poll, faster
  than waiting for a guest report to go stale.
- **Guest-report recency = secondary** app-level signal.

**Backup-deadline checker:** today it is *event-based* — it scans for `backup_completed`/`backup_failed`
events since local midnight and alerts if none. Two changes: (1) **mechanism** — move it to a field
check on `host_reports`' last-backup-per-target (cleaner now that backup state arrives in the host
report); (2) **emitter** — the de-privileged controller no longer runs backups, so the **agent** is the
source of the last-backup status (Part 3 §8). Without re-homing the source, the deadline check would go
silent after the controller stops backing up.

## 5. Desired-state serving

The operator's **intent** (§1 top-down) lives as JSON on `hosts`/`guests` (storage manifest +
policies + golden version on the host; per-guest spec + versions on the guest) with a per-host
`desired_generation`. The agent pulls its host's desired state on poll (with the generation, so it
reconciles only on change and reports which generation it has converged to).

- **Benign convergence** (create a guest, attach storage per policy, bump a version, adjust a
  non-destructive policy) → the agent reconciles freely.
- **Destructive convergence** (guest removal = destroy, storage detach/wipe, data-losing resize) →
  the agent requires a **matching signed op** (§6) before executing that delta; absent/invalid → it
  refuses and reports `pending_signature`.

**Geo is *not* in the agent's desired state** — it's customer→hub→Cloudflare (§7); the agent never
touches WAF.

## 6. Authorization — signed-op queue + editing flow

Implements Part 4's gate on the hub side. The hub holds **no signing key**.

- **`signed_ops`** (new): `op_id, customer_id, host_id, target_guest, op_type, op_blob (canonical
  JSON), signature (armored SSHSIG), status (pending_signature → signed → delivered → executed /
  failed / expired / rejected), nonce, issued_at, expires_at, executed_at, result`.
- **Editing flow:** the operator edits a customer's desired state, reusing the existing config-form +
  diff UX. Note the **transport inverts**: today's "Push" is a hub→box *inbound* POST (forbidden by the
  box-initiated model); here "publish" means **write to desired state, delivered on the next agent/
  controller poll**. The form and diff carry over; the push transport does not. The hub diffs vs current
  and **classifies each delta** (B1 rule):
  - **benign** → published straight to desired state;
  - **destructive** → the hub generates the canonical op blob and routes it through signing.
- **Signing hand-off (Part 4 option (b)):** a local operator CLI (`felhom-sign --pending`) fetches
  the pending blob from the hub, signs it on the workstation with the dedicated key, and posts the
  signature back into `signed_ops`. The hub never sees the key.
- The agent polls `signed_ops` for its host alongside desired state, verifies (Part 4 pipeline),
  executes, and reports status → the hub logs to the existing **`events`** audit trail.
- **Classification lives in both places, with different jobs:** the hub classifies at *edit time*
  for UX (prompt to sign); the **agent's classification is the authoritative guard** (a compromised
  hub could skip the prompt, but the agent still enforces the signature).
- A **pending-ops view** per customer shows the lifecycle (awaiting signature → awaiting agent →
  executed).

## 7. Geo enforcement (Part-2 S4)

The hub already holds the CF API token and already has a remove-all path
(`internal/web/configs.go` `handleGeoDisable` → `cloudflare.RemoveGeoRules`). **But the token is
dual-purpose today** — DNS-01/ACME *and* WAF/geo — and `configgen.Generate` deep-merges it (via
`config_json`) into the generated `controller.yaml`, so it currently ships **down to the box**. Two
things follow:

- **ACME assumption (must be stated, not skipped):** in the Cloudflare-Tunnel-default model the edge
  terminates TLS, so the box needs no public certificate and the **DNS-01/ACME use of the token goes
  away**. Granting that, the token comes fully off the box and lives hub-only. (If any box still does
  DNS-01, the token cannot fully come off — so this assumption is load-bearing.)
- **`configgen` must stop emitting `cf_api_token`** into `controller.yaml` (drop it from the merge /
  relocate it to a hub-only field).

The delta: the **customer sets geo in the controller UI → the controller reports the geo desired-state
up → the hub reconciles it into the Cloudflare WAF** (rather than the box calling the CF API). The hub
keeps the remove-all override for self-lockout. The controller no longer calls the CF API.

## 8. Enrollment (evolution of the existing retrieval-password/config-gen flow)

Today: `GET /config/{id}` with an `X-Retrieval-Password` (Hungarian passphrase) returns a deep-merged
`controller.yaml`. New:

- Enrollment mints the **agent identity first** (the agent then provisions controllers), pins the
  **operator signing public keys** (Part 4 — operational + cold recovery) onto the agent, and the
  agent mints each controller's bootstrap (its hub guest key + local-API token).
- A **restore-mode** re-enrollment (§9) hands an existing identity to a fresh agent.

The existing `configgen` deep-merge + Hungarian-passphrase machinery is the base; it grows the
agent-first + key-pinning + restore-mode steps.

## 9. DR model

The headline: the **old heavy infra-backup push retires** — not because the hub authors everything
(§1 says it doesn't), but because (a) the box-driven mirror already arrives via the §3 report streams,
and (b) the actual app **data + configs live inside the PBS guest snapshot**. So a separate
config+secrets+restic-password infra-backup blob is redundant.

What remains:
- the **report streams** keep the hub's mirror current (storage layout + `durable_id`s, app inventory,
  snapshot pointers) — but this mirror is **convenience, not the DR source of record** (reports are
  pruned by age);
- the agent **escrows the recovery-code-wrapped PBS key** to the hub (the one artifact only the box
  can produce — zero-knowledge: the hub stores it, cannot open it);
- a **slim DR record** on the `hosts` row (PBS namespace + repo fingerprint + the wrapped escrow key).
  These last two are *box-reported* columns on an otherwise operator-intent row — labelled as such so
  the §1 two-driver split stays legible per column.

Both existing infra-backup tables retire — `infra_backup_versions` (the current/live one, all readers
hit it) **and** `infra_backups` (the deprecated legacy mirror). The slim DR record folds onto `hosts`
instead. The **controller's infra-backup push is removed** (it's de-privileged).

**Recovery (host loss):** the new agent re-enrolls in **restore mode**; the hub hands it the durable
record — and DR reads from the **durable sources, not the prunable report mirror**: operator intent
(desired-state on `hosts`/`guests` — identity, tunnel token, storage manifest), the slim DR record
(PBS namespace + repo fingerprint), the **wrapped escrow key**, and **PBS's own snapshot enumeration**
(the agent lists snapshots once it has the namespace + unwrapped key). Guest inventory + app data come
from **inside the PBS guest snapshots**, not from a retained `host_report`, so recovery doesn't degrade
when the last report has aged out. The **customer provides their recovery code at the agent**, which
unwraps the PBS key locally (never sent to the hub); the agent restores guests from PBS, resets
identity, reuses the tunnel. The customer recovery code is the irreducible residual (the premium
operator-managed custody tier avoids it, at the cost of the operator holding the key). The old
controller-targeted `GET /recovery/{id}` is replaced by this agent restore-mode flow.

## 10. What persists from today (unchanged or lightly adapted)

The Customer record (`customer_configs`); config generation/retrieval (`configgen`); the two-tier
notification system (operator English / customer Hungarian, Resend, cooldowns); `events` + audit;
`app_telemetry` / `app_log_issues`; customer lifecycle actions (block/unblock, trigger-update,
delete); the asset manager; and the dashboard — adapted to render the **host + guests** view per
customer instead of a single controller.

## 11. Schema deltas (grounded in store.go's idempotent style; clean cutover)

- **NEW:** `hosts`, `guests`, `host_reports`, `signed_ops`.
- **DROP `reports` + CREATE `guest_reports`** (under the clean cutover this is drop+create with no data
  migration, not an in-place rename); `guest_reports` adds `guest_id`, `host_id`; `cpu/memory` mean
  guest-level; `backup_last_snapshot` goes quiet.
- **ADD** desired-state JSON + `desired_generation` to `hosts`; `desired_spec_json` to `guests`; the
  slim DR record (PBS namespace + repo fingerprint + wrapped escrow key) onto `hosts`.
- **DROP both** `infra_backup_versions` (current/live) **and** `infra_backups` (legacy mirror) — the DR
  record replaces them on `hosts`.
- **KEEP** `customer_configs`, `events`, `customer_notifications`, `notification_log`,
  `app_telemetry`, `app_log_issues`.
- **Authz cleanup the cutover enables:** several endpoints today use global-or-any-customer-key auth
  rather than customer-scoped (the infra-backup GETs, `/notify`). Most retire with the infra-backup
  push; any that carry over should scope to the resolved host/guest → customer under §2.

## 12. Open items
- Operator signing-key operational mechanics (Part 4 §8) — the hub-side pending-op UI is here; the
  key custody/rotation tooling is Part 4's.
- Multi-tenant resource fairness (deferred shared-host case).
- Hub-side desired-state **editing UX** specifics (form/diff wiring) — to be grounded against
  `hub/internal/web/configs.go` at implementation.
- Golden-image refresh cadence / fleet versioning (carried from Part 3 §13).