felhom.eu/documentation/architecture/01-topology-and-trust.md

# Felhom Controller Architecture — Part 1: Topology & Trust

> **How to read this document.** Two kinds of statement appear, and where this document marks them it
> marks them like this — the same wording as `07-backup-architecture.md:11-17`, carried here on
> 2026-08-22 (R-376) so a reader meets one convention and not eight:
>
> - **[DESIGN]** — a decision taken. Not derived from code; the code may not implement it yet.
> - **[FACT]** — an observed property, carrying a `file:line`, a live command output or a citation.
>
> **Statements in this document are NOT yet all marked.** Marking them wholesale is a large judgement
> exercise and a wrong mark is worse than none, so only what a session touches is marked (R-376).
> **An unmarked statement therefore means "not yet classified", never "observed".** That ambiguity is
> exactly what cost this project three sessions in August 2026: the hot/bulk placement decision sat
> unmarked beside a marked `[FACT]`, and was read as an observation and reported as a defect.



**Status:** draft (decisions from the topology/trust design sessions).
**Platform facts** referenced here live in `docs/proxmox-platform.md`; this document
records *Felhom's decisions*, not Proxmox behaviour.

---

## 1. Model at a glance

Three components. **Control is always box-initiated** — the hub never connects *into* a
customer box.

```
        operator side                     customer box (per Proxmox host)
   ┌───────────────────┐         ┌───────────────────────────────────────────┐
   │       HUB         │         │  Proxmox host                              │
   │ (dooplex.hu, k3s) │         │   ┌──────────────┐                         │
   │  - report sink    │◀──poll──┤   │  HOST AGENT  │  operator-tier          │
   │  - signed jobs    │  signed │   │  (Proxmox    │  • all Proxmox ops      │
   │  - dashboard      │  jobs   │   │   token)     │  • provision / restore  │
   │  - customer record│         │   └──────┬───────┘  • storage mgmt         │
   │  - PBS namespace  │         │          │ local constrained API           │
   └─────────▲─────────┘         │   ┌──────▼───────────────────────────────┐ │
             │                   │   │  customer LXC (one per customer)      │ │
             │  direct, app-     │   │   ┌──────────────┐   Docker:          │ │
             └───────────────────┼───┤   │ IN-GUEST     │   [app] [app] ...  │ │
                domain reports   │   │   │ CONTROLLER   │   (Docker containers)│
                                 │   │   │ (Docker-only)│                    │ │
                                 │   │   └──────────────┘                    │ │
                                 │   └───────────────────────────────────────┘ │
                                 └───────────────────────────────────────────┘
   PBS (offsite) ◀── outbound, client-side-encrypted backups ── customer box
   end-users / customer ◀── Cloudflare Tunnel ── apps + controller UI
```

---

## 2. The customer node

- One **Proxmox host** per box (PVE 9.2, Debian 13, LVM-thin).
- **Default workload topology:** one **customer LXC**, Docker inside it, each app a Docker
  container/stack. Apps are isolated at the Docker layer (separate containers, networks,
  volumes, cgroup limits); they share one LXC/kernel/Docker daemon.
- **Escape hatch:** promote an individual app to its own guest (LXC or VM) only for a
  specific reason — a non-Linux/Windows app, a genuinely untrusted or exposed app needing
  hard isolation, or a resource hog needing guarantees.
- **Multi-tenant:** one customer per host is the home default; multiple customer LXCs on
  one host (a company environment) is **not precluded** — the agent manages a *set* of
  guests. The only multi-tenant-specific work deferred to "if it becomes real" is resource
  fairness (per-guest disk/RAM/CPU quotas).
- **A scratch guest is a second guest of the SAME customer, unenrolled** (operator ruling
  2026-09-13, R-481; built as LXC 9202 on demo-hp, persists). The hub ties one host to one
  customer, so a second enrolled customer on a box is not a thing the product does. The scratch
  guest runs with the hub, the tunnel, the agent link, off-site and self-update all off, and its
  controller image is set by hand — the one place that is allowed. Two of its properties were
  *decided by CC unattended — operator may reverse*: **it never binds the customer's real data
  drive** (a throwaway must not be able to reach real data) and **it never starts cloudflared**
  (a second connector would serve the public domain from a scratch box).

---

## 3. Components & responsibilities

| | **Hub** | **Host agent** | **In-guest controller** |
|---|---|---|---|
| Runs on | dooplex.hu (k3s) | the Proxmox host | the customer LXC |
| Tier | operator backend | operator (high-privilege) | customer-facing (app) |
| Holds | customer records, signed-job source, PBS namespaces, escrowed keys | the **only** Proxmox API token; per-host operator identity | **no Proxmox creds**; its own hub API key + a local-API token to the agent |
| Does | reporting sink, dashboard, job queue, source of durable truth | all Proxmox ops (provision, restore, snapshot, backup, storage mgmt, LXC lifecycle); polls hub for signed jobs; exposes a constrained local API to the controller; **per-guest authorization gate** | Docker/app lifecycle, catalog deploy, customer UI, app-level (data-layer) backup; reports app-domain to the hub directly |
| Never does | initiate a connection *into* a box | — | touch the Proxmox API directly |

**Key separation:** the controller manages Docker; the agent manages Proxmox. The controller's
only path to guest-level operations (snapshot-before-deploy, "grow my RAM") is a constrained
**local API call to the agent**, which the agent authorizes (scoped to that controller's own
guest) and executes with its operator-tier token. This consolidates all Proxmox access and
all per-guest authorization in one auditable place and leaves the guest with zero Proxmox
credentials.

---

## 4. Control plane — box-initiated

- CGNAT does **not** force this: the Cloudflare Tunnel already makes a box reachable through
  Cloudflare's edge. We *choose* box-initiated control for the smallest attack surface — the
  box exposes no control endpoint at all.
- The agent and the controller **poll** the hub; the hub never initiates inbound.
- Operator actions are delivered as **signed jobs**: the agent verifies an operator signature
  before executing, so a compromised hub database alone cannot forge commands.
- All operator-initiated actions are recorded in a **customer-visible audit log**.

---

## 5. Trust boundaries

| Boundary | What crosses | Mechanism | Blast radius if breached |
|---|---|---|---|
| end-user ↔ apps | app traffic | Cloudflare Tunnel → Traefik (Host routing) | that app |
| customer ↔ controller UI | management UI | Cloudflare Tunnel; UI auth (bcrypt) | the customer's own box |
| controller ↔ agent | snapshot/resize/backup requests | local constrained RPC; agent authorizes per-guest | the controller's own guest only |
| agent ↔ hub | reports + signed jobs | outbound poll; signed jobs | one box; signed jobs limit forgery |
| controller ↔ hub | app-domain reports/jobs (incl. geo desired-state) | outbound, own API key | app-domain of one customer |
| box ↔ PBS | encrypted backups | outbound; per-customer namespace; client-side encryption | ciphertext only (operator can't read) |
| guest ↔ Proxmox host | **(none direct)** | the guest holds no Proxmox creds; all via the agent | — |
| hub ↔ Cloudflare API | geo-restriction WAF (enforcement) | the **hub** holds the CF API token; reconciles geo desired-state → WAF | the customer's zone/WAF |

---

## 6. Enrollment & identity

- **Physical presence at provisioning** (on-site install, or pre-imaged-and-delivered).
  This removes any zero-touch remote-enrollment problem.
- A **one-time retrieval code** mints durable identity. Single-use (burned on the successful
  config fetch) plus a short *pre-use* TTL; one-click regenerate for the only real failure
  case (fetch fails before anything is persisted). After the fetch, the code is irrelevant —
  everything downstream runs on durable credentials, so retries don't need it.
- **Order:** the agent enrolls first (and, running as root at setup, mints its own scoped
  operator-tier Proxmox token), then provisions the customer LXC from the golden template and
  deploys the controller into it — injecting the controller's hub API key and its local-API
  token. The controller is the agent's product, never the other way around.
- The **hub customer record is the durable source of truth**, and it survives box loss:
  identity, domain, **Cloudflare tunnel token**, **PBS namespace**, **storage manifest**, a
  **mirrored app inventory** (bottom-up reality, not operator-declared intent — apps themselves
  restore from the PBS guest snapshot, never re-deployed from this record; see `05` §1/§9), and the
  **escrowed (zero-knowledge) backup key**. This is what makes hardware replacement possible.

---

## 7. Networking

- **Cloudflare Tunnel** provides inbound access to apps and the controller UI (the CGNAT
  solution). Tunnel token lives in the hub record → **reused on new hardware during DR**, so
  DNS/routing stay intact through an outage.
- **Outbound only** for control/report/backup (poll to hub, push to PBS). No inbound control
  endpoint exists in the chosen model.
- **Every customer has their OWN domain — never a name under `felhom.eu`** (operator ruling
  2026-09-14). The free Cloudflare tier's certificate covers one level below a zone, so nested names
  such as `felhom.<customer>.felhom.eu` are not covered; the customer's own domain is a few thousand
  forints a year and is **included in the customer's price**. The dashboard is `felhom.<customer
  domain>`, each app `<sub>.<customer domain>`. **The tunnel is created by the operator** per
  `runbooks/day0-install.md` A.1 today; the hub creating it at customer creation (for a domain already
  on Cloudflare) is register row R-494, P3, not blocking. Measured reason this was ruled now: the
  2026-09-14 first-hour drill used a `*.felhom.eu` customer domain with no tunnel, and the dashboard link
  in the setup-code mail did not resolve.
- **Tunnel placement: host** (resolved, Part 3 §3/§5). `cloudflared` runs on the Proxmox host
  as its own **agent-managed systemd service** — not inside the guest — so the data path
  survives control-plane death by construction. Geo-restriction WAF is **hub-enforced** (the
  hub holds the CF API token; the controller only reports geo desired-state).

---

## 8. Storage & backup

**Tiers** (escalating failure scope):

| Layer | Mechanism | Survives | Note |
|---|---|---|---|
| Snapshot | LVM-thin snapshot (transient) | *logical* loss only | whole-LXC rollback; **not a backup** |
| Local — second storage | vzdump to `dir`/`nfs`/`cifs` | primary-disk failure (USB) / box death (NAS) | first *real* backup tier |
| Offsite — PBS | dedup'd, incremental, encrypted | site loss | the DR substrate; paid tier |

- **Storage manifest** (hub-held, agent-reconciled): per target → type, durable identity
  (UUID / `server:/export` / repo+fingerprint), **class** (fast/slow + rough IOPS, set once
  at attach), role, encrypted credentials, schedule/retention. The agent creates the Proxmox
  storages, continuously checks presence/reachability, and reports per-target status (a
  disconnected target → actionable notification).
- **[DESIGN] App data placement is per-volume, not per-app:** `.felhom.yml` classifies each volume
  **hot** (DB/config/cache → fast storage, enforced) vs **bulk** (media/files → may be slow).
  A photo app's DB stays on SSD while its blobs go to the USB.

  > **Marked [DESIGN] on 2026-08-22 (R-376), and the pointer is honest about what it can point at.**
  > **This decision was never recorded as a decision anywhere** — it was established by reading, not
  > by citation: it exists as this bullet and nowhere else, with no dated entry in the decision log
  > and no `R-` row. A log entry was written on 2026-08-22 (`CONTEXT.md`, "App data placement is a
  > DECISION") **to give it a home, not to claim it was decided then**; the choice is older than the
  > entry and its original date is not on record.
  >
  > **What being unmarked cost.** The consequence of this bullet — that 40 of 53 catalogue templates
  > declare no configurable path because they are all-hot — is stated as **[FACT]** at
  > `07-backup-architecture.md:296-299`. A reader met a marked observation beside an unmarked choice
  > and reasonably asked whether it *should* be so. **Between 19 and 22 August that reader called this
  > decision a defect in four places** (R-370), and one session's work went into correcting the record
  > rather than into the product.
- **Backup scoping:** hot data (LXC rootfs) rides the guest `vzdump` → tiers + PBS. Bulk data
  on external mount points is **excluded** from the guest vzdump (per-mount `backup` flag) and
  gets its own per-volume policy (file-level to a tier, slower cadence — or explicitly *not*
  backed up for re-downloadable content, with the customer informed).
- **Tiers double as the DR restore-source priority:** restore from the fastest *surviving*
  source (local if still attachable, PBS on true site loss).
- **Key custody (zero-knowledge default):** three tiers the customer chooses —
  *customer-only* / *zero-knowledge escrow (default)* / *operator-managed*. Default escrows
  the **PBS passphrase-protected keyfile** in the hub, wrapped under a **customer recovery
  code** the operator can't open; DR needs the customer's code. Access-notification is an
  audit signal, never the primary guard. (Don't build bespoke crypto — use PBS's native
  keyfile passphrase.)

---

## 9. Disaster recovery

- **Guest-loss (host + agent alive):** the agent restores the guest from the fastest
  surviving tier, **resets identity** (MAC/hostname — see `proxmox-platform.md`), boots it,
  controller returns. Validated mechanics: Phase 2.
- **Host / hardware-loss (agent gone):** re-provision (§6) in **restore mode** — the hub,
  knowing the customer has PBS backups, hands the freshly-enrolled agent the existing identity
  + PBS namespace + a restore directive instead of a clean-provision directive. The agent
  restores from PBS; the controller returns on the same domain (tunnel reused from the hub
  record). DR = provisioning + a restore mode, not a separate mechanism.
- **Snapshot-before-deploy:** controller asks the agent to snapshot, deploys, runs its
  post-deploy health check, asks the agent to roll back on failure. (Transient snapshot, §8.)

---

## 10. How this embodies the product values

- **Zero-knowledge offsite** — the operator holds the offsite backup but cannot read it.
- **Box-initiated control + signed jobs** — no standing operator backdoor; a hub compromise
  alone can't forge commands.
- **Customer-visible audit log** — every operator action is visible to the customer.
- **Never hold data hostage** — subscriptions cover ongoing labour (monitoring, offsite,
  support, new deployments); the customer's data and deployed apps remain recoverable by the
  customer (recovery code), with nothing locked behind the operator.

---

## 11. Open sub-decisions (carried into later parts)

- **RTO/RPO targets** → drive the backup + offsite-replication schedule (§8).
- Offboarding / decommission (scenario 6) — not yet designed; must honour "never hold data
  hostage" in credential revocation + data hand-off.
- Multi-tenant resource fairness — deferred until multi-tenant is real (§2).

---

## Appendix — relationship to the spike

- **Phase 0** → §2: LXC-default for the workload; overhead numbers.
- **Phase 1** → §3/§5: validated the privilege boundary (create/allocate is operator-tier).
  The guest-side scoped-backup-token it proved possible is **not** used — we chose the
  agent-mediated path — but it confirmed restore = operator-tier, which shapes the agent.
- **Phase 2** → §8/§9: backup→restore round-trip; identity reset on restore.

---

## Changelog — design-review + Phase-3 fold-in (2026-06-08)

- §5 trust boundaries: **added `hub ↔ Cloudflare API`** row (hub holds the CF token, enforces
  geo→WAF); controller↔hub row notes it carries geo desired-state (S4).
- §7 networking: **tunnel placement resolved → host** (agent-managed systemd service); geo is
  hub-enforced (S4/S5).
- §11 open items: removed the now-resolved **tunnel placement** and **self-update flow** entries
  (S5; self-update designed in 03 §11).
- §6 durable record: **"declarative app inventory" → "mirrored app inventory"** — aligns the wording
  with the locked two-driver model (`05` §1: apps are bottom-up mirror, never operator-declared;
  `05` §9: apps restore from the PBS guest snapshot, not re-deployed from this record).