# `Rexsilient.Notifier.TelemetryNotifier`
[🔗](https://github.com/fabiobarkoski/rexsilient/blob/v1.0.0/lib/rexsilient/notifier/telemetry.ex#L1)

The default notifier: emits every notification as a `:telemetry` event.

The event name is `[:rexsilient, kind, moment]`, following the
`:telemetry.span/3` conventions: `:before` is emitted as `:start` and
`:after` as `:stop`. The retry `:stop` moment is emitted as `:give_up`, so
it does not clash with the `:stop` event of each attempt.

The numeric keys of the notification's state, `:monotonic_time`,
`:system_time`, `:duration`, `:delay` and `:timeout`, are the measurements;
every other key is metadata. A `:timeout` of `:infinity` stays in the
metadata. See `Rexsilient.Notifier` for what each moment means.

## Events

`[:rexsilient, :circuit_breaker, event]`:

| Event | Measurements | Metadata |
|:------|:-------------|:---------|
| `:start` | `monotonic_time`, `system_time` | `name` |
| `:stop` | `monotonic_time`, `duration` | `name`, `result`, `outcome` |
| `:rejected` | `system_time` | `name` |
| `:open` | `system_time`, `timeout` | `name`, `from`, `outcome`, `forced`¹ |
| `:half_open` | `system_time` | `name`, `from` |
| `:probing` | `system_time`, `timeout` | `name`, `from`, `outcome` |
| `:closed` | `system_time` | `name`, `from`, `forced`¹, `restart`¹ |

¹ Only present when the change was forced with
`Rexsilient.CircuitBreaker.force_open/1` or
`Rexsilient.CircuitBreaker.force_close/1`, or caused by a manager restart.
A forced `:open` has `timeout: :infinity`, in the metadata.

`[:rexsilient, :retry, event]`:

| Event | Measurements | Metadata |
|:------|:-------------|:---------|
| `:start` | `monotonic_time`, `system_time` | `name`, `attempt` |
| `:stop` | `monotonic_time`, `duration` | `name`, `attempt`, `result`, `outcome` |
| `:delay` | `delay` | `name`, `attempt`, `outcome` |
| `:give_up` | `duration` | `name`, `attempt`, `outcome`, `reason` |

`[:rexsilient, :fallback, event]`:

| Event | Measurements | Metadata |
|:------|:-------------|:---------|
| `:start` | `monotonic_time`, `system_time` | `name`, `outcome` (the one replaced) |
| `:stop` | `monotonic_time`, `duration` | `name`, `outcome` |

Times and `duration` are in native time units, `delay` and `timeout` in
milliseconds. `result` is `:success` or `:failure`, and `outcome` is a
`t:Rexsilient.Classify.outcome/0`.

## Example

    :telemetry.attach(
      "log-open-breakers",
      [:rexsilient, :circuit_breaker, :open],
      fn _event, _measurements, %{name: name, from: from}, _config ->
        Logger.warning("breaker #{inspect(name)} opened from #{from}")
      end,
      nil
    )

> #### Handlers run in the calling process {: .info}
>
> Unlike other notifiers, it runs in the calling process, so handlers must be
> fast; see [Process](`m:Rexsilient.Notifier#module-process`).

---

*Consult [api-reference.md](api-reference.md) for complete listing*