# fleet-prometheus

Prometheus instance that is the **source of truth for fleet liveness**. Runs on
the **VPS** (ingress / control-plane host) and is reachable only over Tailscale.

This is a **clean scaffold**: right now it scrapes only itself and the VPS-local
`node_exporter`. The fleet targets, liveness rules, and alerting integration are
deliberately separate, later steps (see *Next steps* below).

## Why separate from the home `prom`

The home `prom` on **PIHA** is LAN-only and monitors the home network. This
instance is intentionally a **distinct** Prometheus dedicated to the distributed
fleet — hence the `fleet-` naming. The split is made explicit in every series:

- `external_labels: { fleet: "homelab-codex" }`
- job names prefixed/scoped for the fleet (`prometheus`, `fleet-node`)

It also avoids two anti-patterns the home `prom` has:

- **No `:latest`** — the image is pinned to `prom/prometheus:v3.5.0` (LTS).
- **No inline secrets** — `prometheus.yml` is secret-free by contract (the home
  prom embeds a plaintext HAOS token; we do not).

## Stack

| Container          | Image                   | Purpose                        |
|--------------------|-------------------------|--------------------------------|
| `fleet-prometheus` | `prom/prometheus:v3.5.0`| Fleet liveness Prometheus (9090) |

## Placement & exposure

- **Node:** VPS (`ubuntu-4gb-hel1-1`, Tailscale `100.95.58.48`).
- **Exposure:** `tailscale-internal` — exposed exactly like `control-plane`: a
  plain published `9090:9090` port with **no** public npm reverse-proxy entry.
  Reachability is constrained to the Tailscale mesh at the VPS firewall layer.
  Do **not** add this to npm or public DNS.
- **Memory:** `mem_limit: 512m`. `oom_score_adj: 200` (positive) — fleet
  monitoring is less critical than the control-plane (`-900`), so it is a
  sacrificial OOM victim *before* the control-plane, never after.
- **Retention:** `15d` / `2GB` (whichever hits first) — tight on purpose.

## Data

TSDB lives in the named volume `fleet-prometheus_tsdb` → `/prometheus`.

## Configuration

- `prometheus.yml` — committed, **secret-free**. Global config + two scrape jobs.
- `env.example` → copy to `.env` (gitignored). Holds `TAILSCALE_BIND_IP`, the
  VPS Tailscale interface IP the listen socket is bound to.

### Deploy — `.env` is mandatory

The port is published as `${TAILSCALE_BIND_IP}:9090:9090` so the socket is bound
**only** to the Tailscale interface, never `0.0.0.0`. Compose auto-loads a
co-located `services/fleet-prometheus/.env`, but if that file is **missing** the
variable resolves to a blank string and Compose **silently binds to 0.0.0.0**
(publicly reachable on the Hetzner IP) — it only warns, it does not fail.

Therefore, before `up -d`:

1. Create `services/fleet-prometheus/.env` from `env.example` with the real
   `TAILSCALE_BIND_IP` (verify with `tailscale ip -4` on the VPS).
2. Deploy with the env file explicit, to be safe:

   ```bash
   docker compose -f services/fleet-prometheus/docker-compose.yml \
     --env-file services/fleet-prometheus/.env up -d
   ```

3. Confirm the bind is Tailscale-only (must NOT show `0.0.0.0`):

   ```bash
   docker compose -f services/fleet-prometheus/docker-compose.yml \
     --env-file services/fleet-prometheus/.env config | grep host_ip
   ```

### Scrape targets (scaffold)

| Job          | Target                      | Notes                                   |
|--------------|-----------------------------|-----------------------------------------|
| `prometheus` | `localhost:9090`            | self                                    |
| `fleet-node` | `host.docker.internal:9100` | VPS `node_exporter` (runs `network_mode: host`, listens on host `:9100`); reached via `host-gateway` |

## Verify

```bash
# Config is syntactically valid (uses promtool inside the image):
docker run --rm -v "$PWD/services/fleet-prometheus/prometheus.yml":/etc/prometheus/prometheus.yml:ro \
  prom/prometheus:v3.5.0 promtool check config /etc/prometheus/prometheus.yml

# Compose renders:
docker compose -f services/fleet-prometheus/docker-compose.yml config

# After `up -d`:
curl -sf http://localhost:9090/-/healthy
curl -s http://localhost:9090/api/v1/targets | jq '.data.activeTargets[].health'
./services/fleet-prometheus/healthcheck.sh
```

## Next steps (NOT done in this scaffold)

- **Fleet targets:** add the `100.x` Tailscale `node_exporter`s for SATURN,
  SOLARIA, PIHA, CHELSTY to the `fleet-node` job.
- **Liveness rules:** `rule_files` with `up == 0 for: 5m` (placeholder is
  commented in `prometheus.yml`).
- **Alerting:** Alertmanager wiring, and/or `brain-watchdog` querying the
  firing alerts API → Telegram (placeholder commented in `prometheus.yml`).
