---
name: fleet-host-process-service-wiring
description: "Add a host-process (non-quadlet) systemd USER service/exporter to serverAppConfigs — every file that must change together, with the signal-relay precedent and the Prometheus gateway/LAN reach rules."
---

A host-process service (runs `python3`/a binary on the host, NOT a container) is the right shape when the thing must read host-only state (DRM/cgroup sysfs, `shells to nvidia-smi`, signal-cli) that a container cannot reach without passthrough. Precedent to mirror: `scripts/signal-relay.{py,service}` + `install_signal_relay` in `deploy-remote.sh`. A new one landed 2026-10-20: `scripts/gpu-exporter.{py,service}` + `deploy_gpu_exporter`.

## The unit is a USER unit, not a quadlet
- Hand-written `scripts/<svc>.service`: `[Service]` `ExecStart=/usr/bin/python3 /home/dank/serverAppConfigs/scripts/<svc>.py` (runs straight from the git checkout — a pull updates it, no copy step), `Restart=always`, `[Install] WantedBy=default.target`.
- It CAN be `systemctl --user enable`-ed (generated quadlet units cannot on this host's podman generator). With `Linger=yes` for `dank`, `[Install]`+`enable` is the whole boot story.

## Every file that MUST change together (a lone change on one side fails silently)
1. `scripts/<svc>.service` — the unit. Base binds **loopback only**; the LAN address is added by a deploy **drop-in**, so the checked-in unit is never a wildcard.
2. `scripts/deploy-remote.sh`:
   - a `deploy_<svc>()` function: `cp` the unit to `~/.config/systemd/user/`, write a `<svc>.service.d/bind.conf` drop-in with the per-host `Environment=..._BINDS=127.0.0.1,<lan>` (map LAN from `$TARGET`: dankclaw=192.168.0.143, dankserver=192.168.0.235 — do NOT hardcode one host if it runs on both), `daemon-reload`, `systemctl --user enable`+`restart`, then a **loop health gate** (`for i in $(seq 1 15); curl -fsS -m5 http://127.0.0.1:<port>/metrics && return; sleep 1`) — a one-shot curl races the bind and once failed a healthy deploy.
   - a dispatcher branch `<svc>) deploy_<svc> ;;` in the central `case "$service"` (near the observability branch).
   - an **allowlist entry on EVERY target** it runs on: `dankclaw:<svc>` and/or `dankserver:<svc>` (the allowlist `case` around the top of the file).
3. `scripts/deploy-plan.py`: add `"<svc>"` to `SERVICE_ORDER`, to `DANKCLAW_SERVICES`/`DANKSERVER_SERVICES` (whichever it runs on), and a `scripts/<svc>.*` path-map in the `parts[0] == "scripts"` block: `if name in {"<svc>.py","<svc>.service"}: _add(services, "<svc>")`. `target_services` then filters per target.
4. `scripts/test-changed.sh`: a `case` routing `scripts/<svc>.py|scripts/<svc>.service` → its seam + `deployment_scoping.bats` (place before the generic fallbacks). `tests/run.sh` runs all `*.bats` regardless, so the mandatory gate is covered even if this route is missing — but add it for focused runs.
5. `shared/prometheus/prometheus.yml`: one scrape job per host, using the **reach rules** (below).
6. Dashboard JSON + the owning page under `serverAppConfigs-docs/Infrastructure/Observability.md` (one owner per fact).

## Prometheus reach rules (the whole cross-file contract)
Prometheus is a **bridge container**. On this netavark host a bridge container CANNOT dial the host's own LAN IP at a host-bind (only at a *published* port). Therefore:
- **Same host (Dankclaw):** scrape `host.containers.internal:<port>` (netavark delivers it to the host LAN bind). Scraping `192.168.0.143:<port>` reads DOWN forever even though the endpoint is healthy.
- **Different host (Dankserver):** plain LAN `192.168.0.235:<port>` reaches it.
- Never target a `*.franksdank.cloud` vhost — Prometheus cannot solve an Anubis challenge; it is red by construction.
- The exporter must bind BOTH loopback and the host LAN (like `node-exporter`/`cadvisor`), so `host.containers.internal` and the LAN both land.

## Firewall
Leave it LAN-open like node-exporter/cadvisor (unauthenticated metrics on the LAN is the repo's exporter posture). Only signal-relay gets an iptables allowlist (loopback+host+`10.89.0.0/16`+DROP) because it is an unauthenticated message-SENDING webhook — do not copy that lock onto a read-only exporter.

## Seam test (tests/<svc>.bats) pattern
- Black-box the binary with injectable inputs (fixture dirs / stub commands), assert only consumer-visible output; assert **absent means absent** (anchor guards to a sample line `^metric{`, not the always-emitted `# TYPE` header — grepping the bare family name matches the header and false-fails).
- Cross-file contracts (grep the other files): the unit's `ExecStart`/bind posture, the deploy function + allowlist + dispatch + health gate, the planner selection (run `deploy-plan.py --target T --paths scripts/<svc>.py`, assert output == `<svc>` per target), the prometheus targets, the dashboard `json.load` + that its `targets[].expr` reference the emitted families.

## Gotchas hit while building gpu-exporter
- Values are float-normalised (`397.40`→`397.4`); a test pinning the literal fails — assert the normalised value. Derive expected byte counts from real units (MiB×1048576, sysfs µW/1e6, temp1_input/1000), don't guess the multiply.
- `xdg-open <PR-URL>` after opening the PR (repo law) — don't make Frank hunt in Gitea.