# Felhom Controller Architecture — Part 1: Topology & Trust **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). --- ## 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 | 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 | — | --- ## 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**, **declarative app inventory**, 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. - **OPEN:** Cloudflare Tunnel placement — host vs guest (`cloudflared` on the Proxmox host routing to guest services, or inside the customer LXC). To resolve in a later part. --- ## 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). - **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. - **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) - Cloudflare Tunnel placement: host vs guest (§7). - **RTO/RPO targets** → drive the backup + offsite-replication schedule (§8). - Self-update flow (scenario 5) — not yet designed. - 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.