# Alerting

Alert rules evaluate every metric that flows through `record_metric()`. There is no separate polling process — evaluation is inline with every metric write.

---

## How It Works

When any monitor or plugin calls `record_metric()`:

1. The metric value is written to the `plugin_metrics` table
2. All enabled `AlertRule` rows matching `(source_module, resource_name, metric_name)` are loaded
3. Each matching rule is evaluated against the new value
4. If a state transition occurs, an `AlertEvent` row is written
5. Notification I/O is deferred outside the transaction via `asyncio.create_task()`

**Key function:** `steward/core/alerts.py` → `record_metric(session, source_module, resource_name, metric_name, value)`

`record_metric()` must always be called inside an active transaction:

```python
async with session.begin():
    await record_metric(session, "ping", "my-server", "response_time_ms", 42.3)
```

Notifications are sent via `asyncio.create_task()` after the function returns, so no network I/O blocks the DB transaction.

---

## Alert State Machine

Each `AlertRule` has one associated `AlertState` row. The state transitions are:

```
inactive ──(breached)──► pending ──(consecutive count met)──► FIRING
                │                                               │
                └──(recovered)──► inactive (no notification)   │
                                                               │
                                          FIRING ──(recovered)──► RESOLVED ──► inactive
                                          FIRING ──(acknowledged)──► ACKNOWLEDGED
                                          ACKNOWLEDGED ──(recovered)──► RESOLVED ──► inactive
                                          ACKNOWLEDGED ──(re-breached)──► FIRING
```

`RESOLVED` is transient — the evaluator writes the event and immediately sets state back to `inactive` within the same transaction. `RESOLVED` never persists as a final state in the DB.

### State Definitions

| State | Meaning |
|---|---|
| `inactive` | Threshold not breached |
| `pending` | Threshold breached but consecutive count not yet met; no notification sent |
| `firing` | Consecutive count met; FIRING notification sent |
| `acknowledged` | Operator acknowledged; suppresses repeat notifications; auto-clears on recovery |
| `resolved` | Transient — notification sent, immediately transitions to `inactive` |

---

## Creating Alert Rules

Alert rules are created in the UI at `/alerts/`. Each rule requires:

- **Name** — human-readable label
- **Source module** — `ping`, `dns`, `traefik`, or any plugin name
- **Resource name** — host name, router name, etc. (must match exactly what the monitor writes)
- **Metric name** — the metric key (e.g. `response_time_ms`, `up`, `error_rate_5xx_pct`)
- **Operator** — `>`, `<`, `>=`, `<=`, `==`, `!=`
- **Threshold** — numeric value
- **Consecutive failures required** — how many consecutive breaches before FIRING (default 1)

### Available Metrics by Module

| `source_module` | `metric_name` | Description |
|---|---|---|
| `ping` | `response_time_ms` | Probe latency (0.0 if down) |
| `ping` | `up` | 1.0 = up, 0.0 = down |
| `dns` | `resolved` | 1.0 = resolved, 0.0 = failed |
| `dns` | `ip_changed` | 1.0 = IP changed from previous result |
| `traefik` | `request_rate` | Requests per second |
| `traefik` | `error_rate_4xx_pct` | 4xx errors as % of requests |
| `traefik` | `error_rate_5xx_pct` | 5xx errors as % of requests |
| `traefik` | `latency_p50_ms` | Approximate p50 latency (ms) |
| `traefik` | `latency_p95_ms` | Approximate p95 latency (ms) |
| `traefik` | `latency_p99_ms` | Approximate p99 latency (ms) |

---

## Notifications

Notifications fire on `FIRING` and `RESOLVED` transitions. All configured channels receive every notification; there is no per-rule channel routing.

### Email

Configured at `/settings/` under SMTP. Settings:

| Setting key | Description |
|---|---|
| `smtp.host` | SMTP server |
| `smtp.port` | Port (default 587) |
| `smtp.tls` | STARTTLS (default true) |
| `smtp.username` | Login |
| `smtp.password` | Password |
| `smtp.recipients` | List of email addresses |

Email is skipped if `smtp.host` is empty.

### Webhook

Configured at `/settings/` under Webhook. The body is a Jinja2 template rendered to JSON. Content-Type is always `application/json`. If the rendered template is not valid JSON, the delivery is logged as failed and no request is sent.

| Template variable | Type | Description |
|---|---|---|
| `alert.rule_name` | str | Alert rule name |
| `alert.state` | str | `FIRING` or `RESOLVED` |
| `alert.metric` | str | Metric name |
| `alert.value` | float | Current value |
| `alert.threshold` | float | Configured threshold |
| `alert.resource` | str | Resource name |
| `alert.source_module` | str | `ping`, `dns`, `traefik`, etc. |
| `alert.timestamp` | str | ISO 8601 UTC |

Default template (Discord-compatible):
```json
{"content": "**{{ alert.state }}** — {{ alert.resource }} — {{ alert.rule_name }} ({{ alert.metric }} = {{ alert.value }})"}
```

Webhook is skipped if `webhook.url` is empty.

---

## Data Models

Defined in `steward/models/alerts.py`:

- **`alert_rules`** — one row per configured rule
- **`alert_states`** — one row per rule, tracks current state and consecutive failure count
- **`alert_events`** — append-only log of all state transitions and notification outcomes
- **`plugin_metrics`** — all metric values written by any monitor or plugin