# Which box do I break? — target selection by blast radius

> Read before picking a machine for a drill, a destructive test, or a throwaway VM. It answers one
> question: *what is safe to lose.* Reachability is in `CLAUDE.md`; hardware in `operations/nodes.md`.
> Added 2026-07-30.

## The rule

> **Start at Tier 0 and work down only if Tier 0 genuinely cannot host the work.**
> **A Tier 2 machine is used only when a task says so explicitly** — never by inference from what was
> not forbidden. An absent fence is not permission. If no tier fits, **stop and ask.**

Fences name **acts**, not machines. "Do not re-target demo-hp's backup target" and "do not use demo-hp
to host a throwaway VM" are unrelated; only the first has ever been meant. Read a per-machine
prohibition as covering the act it names and nothing more.

| Tier | Meaning | Machines |
|---|---|---|
| **0 — disposable. Reach here first.** | Exists to be broken; reinstalling is a routine afternoon, not an incident. **A drill that needs a victim uses one of these.** | `demo-hp` (t740), `demo-felhom` (N100) |
| **1 — create and destroy freely** | Throwaway VMs, guests, scratch customers — **hosted on a Tier 0 machine** | drill VMs, scratch guests |
| **2 — precious. Never a drill target.** | Losing it costs the recovery chain or a real relationship | **DooPlex**, **Peti's cluster**, **ep0** + the Hetzner Storage Boxes |

**DooPlex is Tier 2 because it *is* the recovery chain** — hub, Gitea, registry, PBS, k3s + Longhorn.
Everything else rebuilds from it; it rebuilds from nothing. A bad moment in a DR drill there costs the
thing under test, the source of truth for it, and the backups, at once.

**Standing ruling, 2026-07-25 (`operations/nodes.md`):** drill and build VMs live on the **t740** — not
felhom-pve, and **moved off DooPlex**. This page exists because that ruling sat where no session reads.

## Per machine — permitted / needs care / forbidden

### `demo-hp` — HP t740 · **Tier 0 · the designated drill + build VM host**

- **Freely:** host nested drill VMs; create/destroy guests and scratch customers; reinstall the box.
  **This is the default answer to "where do I run this".**
- **Care:** `local-lvm` is a **thin pool, over-subscribed** (~144 GiB allocated over ~54 GiB) backing
  live guest 9201 — filling it corrupts every guest. Put VM disks on a dir storage at
  **`/mnt/nvme-1tb`, at its root** (a subdirectory fails the agent's `exactMount` check → storage reads
  `disconnected` forever). **That warning is about one storage, not the box.** `/mnt/nvme-1tb` is also
  the `felhom-backup` target and the enrolled user-data drive, so remove scratch storages when done.
- **Forbidden:** do not re-target its backup configuration (below). Do not destroy or unblock
  **`drill-r50` (VM 300)** — the only drift fixture (R-93). No baked SSH key; access is the hub-vaulted
  G1 break-glass password (R-61).

### `demo-felhom` — N100 · **Tier 0**

- **Freely:** create/destroy guests and scratch customers; reinstall the box.
- **Care:** it carries the **PBS-DR / offsite tier** (demo-hp has none), so it is the Tier 0 box whose
  backup chain a test can actually disturb. Prefer demo-hp, per the 2026-07-25 ruling.
- **Forbidden:** do not re-target its backup configuration.

**Both Tier 0 boxes, one shared prohibition and its reason:** do not re-point either backup target.
They are the only two **correctly configured** boxes, so they are the regression path new installer
logic is measured against — losing that reference costs more than the box does.

### `DooPlex` — 192.168.0.180 · **Tier 2**

- **Freely:** build, push images, `sudo kubectl`, read anything. Work inside `/mnt/5_hdd/felhom.eu/`.
- **Care:** the golden-bake nested VM `drill/drill.qcow2` lives here and is an accepted exception **for
  bakes** (last used 0.185.1, 2026-07-29). Using it as a *drill victim* is not covered by that exception
  and contradicts the 2026-07-25 ruling. If touched, restore `qemu-img snapshot -a virgin`.
- **Forbidden:** no global Docker cleanup; do not touch k3s data dirs, Longhorn mounts, PBS datastores
  or Gitea storage; no destructive disk/guest ops; never run CC here with prompts disabled; abort large
  builds if `df -h /mnt/5_hdd /` shows either over 90 %. **Because it is the recovery chain and a live
  k3s node.**

### `Peti's cluster` (`peti-felhom`) — **Tier 2**

**Do not touch, at all.** A real external pilot with a real person behind it; its whole-guest backup
still shares a device with its guest, so a drive failure is **offsite-only recovery**. Deliberately not
migrated, parked until the tester reinstalls (`PETI` in `backlog/OPEN-ITEMS.md`). Currently DOWN, no
enrolled host. No access route from DooPlex, and nothing here needs one.

### `ep0` (`felhom-hetzner`, `ep0.felhom.eu`) + the Hetzner Storage Boxes — **Tier 2**

Reads are fine. It is the **offsite of last resort** (PBS-DR datastore, WireGuard hub, operator OOB
path) and RAM-constrained (3.8 GB, R-90) so a large restore can OOM it. Do not delete datastores, prune
jobs, tunnel config or nftables rules; never a drill target. The Storage Boxes hold the restic copy —
customer documents and photos, on a credential that can still delete (R-95).
**Access: `ssh root@167.233.158.164` from DooPlex** — *not* `felhom-pve → 10.77.0.1`, the route that
produced a false "unreachable" verdict (standing rule 2).

### Tier 1 — drill VMs, scratch guests, scratch customers

Create and destroy freely **on a Tier 0 host**. Two exceptions: **`drill-r50`** is a fixture, not
scratch; and scratch **customers** outlive their VMs in the hub — delete those too, or they accumulate
(`sess-c` and `sess-d` were both left behind before anyone noticed).

#### A fixture may prove a mechanism. Only a fresh box may prove a path.

Rebuilding from scratch every time is waste; reusing a box is legitimate — but not for every claim.

- **Reusable fixture** — a snapshot-reset VM on a Tier 0 host. Use it for **mechanism** work: payload
  capture, fix cycles, anything whose claim is about *code behaviour*. Reset to `virgin` between runs.
  Fast, repeatable, and the right default for iteration.
- **Fresh day-0 from the ISO** — required for any claim about the **install path, the golden image,
  agent publish/vouch, or first-boot state**. Slow, and the only thing that catches the drift family:
  **R-111** (the golden's agent 17 releases behind), **R-115** (an agent built and deployed but never
  published), **R-120** (the golden a controller release behind).

**A fixture must record its provenance** — which golden, agent and controller it was built from, and
when — alongside the VM. A fixture whose versions drift silently is R-120's mechanism turned into a
permanent installation, and it is *worse* than no fixture, because it produces confident wrong results
quickly.

**Worked example.** R-116's closing run deliberately did a real day-0 from the v1.25.0 ISO on demo-hp
instead of reusing the standing fixture. **That is how R-120 surfaced** — the fresh box installed the
golden's controller, which is a release behind, and showed the customer the wrong absent-target message.
The fixture would have shown a controller nobody installs.

## Not established — unknown, not guessed

- **Hetzner Storage Boxes** (`storage-box-pool-1`, `PBS-storage-1` / u629193 / box 611421) — state taken
  from `backlog/OPEN-ITEMS.md`; **no direct access attempted or confirmed.** Tier 2 by what they hold.
- **`felhotest`** (legacy, `ssh -p 33022 kisfenyo@router.abonet.hu`) — **`Connection refused`**
  2026-07-30; that was the only route tried. Untiered; assume nothing.
- **Peti's cluster** hardware/storage layout — unverified. Tier 2 rests on the relationship, which
  needs no verification.

## The gap this page closes

During the R-116 diagnosis session (2026-07-30) a nested-Proxmox drill ran **on DooPlex**, a Tier 2
machine. Not a newly provisioned VM — the standing golden-bake fixture, booted from `virgin` and
restored to it, so nothing was lost. But it was chosen because DooPlex was the only machine no spec had
fenced, while the ruling naming the t740 sat in `operations/nodes.md` with nothing pointing at it.
**The designation existed and was unreachable** — the same class as an absent signal read as a positive
one.