220 lines
13 KiB
Markdown
220 lines
13 KiB
Markdown
# Felhom Controller Architecture — Part 1: Topology & Trust
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**Status:** draft (decisions from the topology/trust design sessions).
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**Platform facts** referenced here live in `docs/proxmox-platform.md`; this document
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records *Felhom's decisions*, not Proxmox behaviour.
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---
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## 1. Model at a glance
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Three components. **Control is always box-initiated** — the hub never connects *into* a
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customer box.
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```
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operator side customer box (per Proxmox host)
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┌───────────────────┐ ┌───────────────────────────────────────────┐
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│ HUB │ │ Proxmox host │
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│ (dooplex.hu, k3s) │ │ ┌──────────────┐ │
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│ - report sink │◀──poll──┤ │ HOST AGENT │ operator-tier │
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│ - signed jobs │ signed │ │ (Proxmox │ • all Proxmox ops │
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│ - dashboard │ jobs │ │ token) │ • provision / restore │
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│ - customer record│ │ └──────┬───────┘ • storage mgmt │
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│ - PBS namespace │ │ │ local constrained API │
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└─────────▲─────────┘ │ ┌──────▼───────────────────────────────┐ │
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│ │ │ customer LXC (one per customer) │ │
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│ direct, app- │ │ ┌──────────────┐ Docker: │ │
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└───────────────────┼───┤ │ IN-GUEST │ [app] [app] ... │ │
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domain reports │ │ │ CONTROLLER │ (Docker containers)│
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│ │ │ (Docker-only)│ │ │
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│ │ └──────────────┘ │ │
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│ └───────────────────────────────────────┘ │
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└───────────────────────────────────────────┘
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PBS (offsite) ◀── outbound, client-side-encrypted backups ── customer box
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end-users / customer ◀── Cloudflare Tunnel ── apps + controller UI
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```
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---
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## 2. The customer node
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- One **Proxmox host** per box (PVE 9.2, Debian 13, LVM-thin).
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- **Default workload topology:** one **customer LXC**, Docker inside it, each app a Docker
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container/stack. Apps are isolated at the Docker layer (separate containers, networks,
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volumes, cgroup limits); they share one LXC/kernel/Docker daemon.
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- **Escape hatch:** promote an individual app to its own guest (LXC or VM) only for a
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specific reason — a non-Linux/Windows app, a genuinely untrusted or exposed app needing
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hard isolation, or a resource hog needing guarantees.
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- **Multi-tenant:** one customer per host is the home default; multiple customer LXCs on
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one host (a company environment) is **not precluded** — the agent manages a *set* of
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guests. The only multi-tenant-specific work deferred to "if it becomes real" is resource
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fairness (per-guest disk/RAM/CPU quotas).
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---
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## 3. Components & responsibilities
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| | **Hub** | **Host agent** | **In-guest controller** |
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|---|---|---|---|
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| Runs on | dooplex.hu (k3s) | the Proxmox host | the customer LXC |
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| Tier | operator backend | operator (high-privilege) | customer-facing (app) |
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| 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 |
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| 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 |
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| Never does | initiate a connection *into* a box | — | touch the Proxmox API directly |
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**Key separation:** the controller manages Docker; the agent manages Proxmox. The controller's
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only path to guest-level operations (snapshot-before-deploy, "grow my RAM") is a constrained
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**local API call to the agent**, which the agent authorizes (scoped to that controller's own
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guest) and executes with its operator-tier token. This consolidates all Proxmox access and
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all per-guest authorization in one auditable place and leaves the guest with zero Proxmox
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credentials.
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---
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## 4. Control plane — box-initiated
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- CGNAT does **not** force this: the Cloudflare Tunnel already makes a box reachable through
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Cloudflare's edge. We *choose* box-initiated control for the smallest attack surface — the
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box exposes no control endpoint at all.
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- The agent and the controller **poll** the hub; the hub never initiates inbound.
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- Operator actions are delivered as **signed jobs**: the agent verifies an operator signature
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before executing, so a compromised hub database alone cannot forge commands.
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- All operator-initiated actions are recorded in a **customer-visible audit log**.
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---
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## 5. Trust boundaries
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| Boundary | What crosses | Mechanism | Blast radius if breached |
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|---|---|---|---|
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| end-user ↔ apps | app traffic | Cloudflare Tunnel → Traefik (Host routing) | that app |
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| customer ↔ controller UI | management UI | Cloudflare Tunnel; UI auth (bcrypt) | the customer's own box |
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| controller ↔ agent | snapshot/resize/backup requests | local constrained RPC; agent authorizes per-guest | the controller's own guest only |
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| agent ↔ hub | reports + signed jobs | outbound poll; signed jobs | one box; signed jobs limit forgery |
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| controller ↔ hub | app-domain reports/jobs (incl. geo desired-state) | outbound, own API key | app-domain of one customer |
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| box ↔ PBS | encrypted backups | outbound; per-customer namespace; client-side encryption | ciphertext only (operator can't read) |
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| guest ↔ Proxmox host | **(none direct)** | the guest holds no Proxmox creds; all via the agent | — |
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| hub ↔ Cloudflare API | geo-restriction WAF (enforcement) | the **hub** holds the CF API token; reconciles geo desired-state → WAF | the customer's zone/WAF |
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---
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## 6. Enrollment & identity
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- **Physical presence at provisioning** (on-site install, or pre-imaged-and-delivered).
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This removes any zero-touch remote-enrollment problem.
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- A **one-time retrieval code** mints durable identity. Single-use (burned on the successful
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config fetch) plus a short *pre-use* TTL; one-click regenerate for the only real failure
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case (fetch fails before anything is persisted). After the fetch, the code is irrelevant —
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everything downstream runs on durable credentials, so retries don't need it.
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- **Order:** the agent enrolls first (and, running as root at setup, mints its own scoped
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operator-tier Proxmox token), then provisions the customer LXC from the golden template and
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deploys the controller into it — injecting the controller's hub API key and its local-API
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token. The controller is the agent's product, never the other way around.
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- The **hub customer record is the durable source of truth**, and it survives box loss:
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identity, domain, **Cloudflare tunnel token**, **PBS namespace**, **storage manifest**,
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**declarative app inventory**, and the **escrowed (zero-knowledge) backup key**. This is
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what makes hardware replacement possible.
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---
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## 7. Networking
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- **Cloudflare Tunnel** provides inbound access to apps and the controller UI (the CGNAT
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solution). Tunnel token lives in the hub record → **reused on new hardware during DR**, so
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DNS/routing stay intact through an outage.
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- **Outbound only** for control/report/backup (poll to hub, push to PBS). No inbound control
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endpoint exists in the chosen model.
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- **Tunnel placement: host** (resolved, Part 3 §3/§5). `cloudflared` runs on the Proxmox host
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as its own **agent-managed systemd service** — not inside the guest — so the data path
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survives control-plane death by construction. Geo-restriction WAF is **hub-enforced** (the
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hub holds the CF API token; the controller only reports geo desired-state).
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---
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## 8. Storage & backup
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**Tiers** (escalating failure scope):
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| Layer | Mechanism | Survives | Note |
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| Snapshot | LVM-thin snapshot (transient) | *logical* loss only | whole-LXC rollback; **not a backup** |
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| Local — second storage | vzdump to `dir`/`nfs`/`cifs` | primary-disk failure (USB) / box death (NAS) | first *real* backup tier |
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| Offsite — PBS | dedup'd, incremental, encrypted | site loss | the DR substrate; paid tier |
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- **Storage manifest** (hub-held, agent-reconciled): per target → type, durable identity
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(UUID / `server:/export` / repo+fingerprint), **class** (fast/slow + rough IOPS, set once
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at attach), role, encrypted credentials, schedule/retention. The agent creates the Proxmox
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storages, continuously checks presence/reachability, and reports per-target status (a
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disconnected target → actionable notification).
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- **App data placement is per-volume, not per-app:** `.felhom.yml` classifies each volume
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**hot** (DB/config/cache → fast storage, enforced) vs **bulk** (media/files → may be slow).
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A photo app's DB stays on SSD while its blobs go to the USB.
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- **Backup scoping:** hot data (LXC rootfs) rides the guest `vzdump` → tiers + PBS. Bulk data
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on external mount points is **excluded** from the guest vzdump (per-mount `backup` flag) and
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gets its own per-volume policy (file-level to a tier, slower cadence — or explicitly *not*
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backed up for re-downloadable content, with the customer informed).
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- **Tiers double as the DR restore-source priority:** restore from the fastest *surviving*
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source (local if still attachable, PBS on true site loss).
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- **Key custody (zero-knowledge default):** three tiers the customer chooses —
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*customer-only* / *zero-knowledge escrow (default)* / *operator-managed*. Default escrows
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the **PBS passphrase-protected keyfile** in the hub, wrapped under a **customer recovery
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code** the operator can't open; DR needs the customer's code. Access-notification is an
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audit signal, never the primary guard. (Don't build bespoke crypto — use PBS's native
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keyfile passphrase.)
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---
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## 9. Disaster recovery
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- **Guest-loss (host + agent alive):** the agent restores the guest from the fastest
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surviving tier, **resets identity** (MAC/hostname — see `proxmox-platform.md`), boots it,
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controller returns. Validated mechanics: Phase 2.
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- **Host / hardware-loss (agent gone):** re-provision (§6) in **restore mode** — the hub,
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knowing the customer has PBS backups, hands the freshly-enrolled agent the existing identity
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+ PBS namespace + a restore directive instead of a clean-provision directive. The agent
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restores from PBS; the controller returns on the same domain (tunnel reused from the hub
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record). DR = provisioning + a restore mode, not a separate mechanism.
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- **Snapshot-before-deploy:** controller asks the agent to snapshot, deploys, runs its
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post-deploy health check, asks the agent to roll back on failure. (Transient snapshot, §8.)
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---
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## 10. How this embodies the product values
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- **Zero-knowledge offsite** — the operator holds the offsite backup but cannot read it.
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- **Box-initiated control + signed jobs** — no standing operator backdoor; a hub compromise
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alone can't forge commands.
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- **Customer-visible audit log** — every operator action is visible to the customer.
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- **Never hold data hostage** — subscriptions cover ongoing labour (monitoring, offsite,
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support, new deployments); the customer's data and deployed apps remain recoverable by the
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customer (recovery code), with nothing locked behind the operator.
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---
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## 11. Open sub-decisions (carried into later parts)
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- **RTO/RPO targets** → drive the backup + offsite-replication schedule (§8).
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- Offboarding / decommission (scenario 6) — not yet designed; must honour "never hold data
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hostage" in credential revocation + data hand-off.
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- Multi-tenant resource fairness — deferred until multi-tenant is real (§2).
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---
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## Appendix — relationship to the spike
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- **Phase 0** → §2: LXC-default for the workload; overhead numbers.
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- **Phase 1** → §3/§5: validated the privilege boundary (create/allocate is operator-tier).
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The guest-side scoped-backup-token it proved possible is **not** used — we chose the
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agent-mediated path — but it confirmed restore = operator-tier, which shapes the agent.
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- **Phase 2** → §8/§9: backup→restore round-trip; identity reset on restore.
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---
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## Changelog — design-review + Phase-3 fold-in (2026-06-08)
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- §5 trust boundaries: **added `hub ↔ Cloudflare API`** row (hub holds the CF token, enforces
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geo→WAF); controller↔hub row notes it carries geo desired-state (S4).
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- §7 networking: **tunnel placement resolved → host** (agent-managed systemd service); geo is
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hub-enforced (S4/S5).
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- §11 open items: removed the now-resolved **tunnel placement** and **self-update flow** entries
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(S5; self-update designed in 03 §11). |