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# Otel

Pure Elixir, [OpenTelemetry](https://opentelemetry.io/)-compatible

## Features

- **Signals**
  - Traces
  - Metrics
  - Logs
- **Propagators**
  - W3C TraceContext
  - W3C Baggage
- **Exporters**
  - OTLP/HTTP (Protobuf)
- **Integrations**
  - `:logger` bridge
  - `:telemetry` bridge

## Requirements

- Elixir `~> 1.18`
- Erlang/OTP `~> 26.2`

## Compatibility

| Component | Version |
|---|---|
| OpenTelemetry Specification | `v1.55.0` (Stable signals only) |
| OpenTelemetry Protocol (OTLP) | `v1.10.0` |
| W3C Trace Context | Level 2 (REC) |
| W3C Baggage | OTel Stable Baggage Propagator wire format |

## Installation

Add `:otel` to `deps` in `mix.exs`:

```elixir
def deps do
  [
    {:otel, "~> 0.4.0"}
  ]
end
```

## Configuration

### SDK

```elixir
# config/config.exs
config :otel, otp_app: :my_app, req_options: []
```

`:req_options` is forwarded to `Req.new/1` — see [`:req`](https://hexdocs.pm/req) for the full option list.

### Logs

```elixir
# config/config.exs
config :kernel,
  logger: [
    {:handler, :otel, Otel.LoggerHandler, %{}}
  ]
```

`Otel.LoggerHandler` bridges `Logger` — see [`:logger`](https://www.erlang.org/doc/apps/kernel/logger.html) for log levels and metadata.

### Metrics

```elixir
# lib/my_app/application.ex
children = [
  {Otel.TelemetryReporter, metrics: []}
]
```

`Otel.TelemetryReporter` bridges `Telemetry.Metrics` — see [`:telemetry_metrics`](https://hexdocs.pm/telemetry_metrics) for metric definitions.

### Trace

```elixir
# lib/my_app/application.ex
children = [
  {Otel.TelemetryTracer, events: []}
]
```

`Otel.TelemetryTracer` bridges `:telemetry.span/3` — see [`:telemetry`](https://hexdocs.pm/telemetry) for instrumentation.

#### Optional: `Otel.TelemetrySpanDecorator`

```elixir
# lib/my_app/calculator.ex
defmodule MyApp.Calculator do
  use Otel.TelemetrySpanDecorator

  @span [:my_app, :calculator, :add]
  def add(a, b), do: a + b

  @span event: [:my_app, :calculator, :sub], capture_io: true
  def sub(a, b), do: a - b
end
```

`@span` auto-wraps the function body in `:telemetry.span/3` and injects `code.function.name` / `code.file.path` / `code.line.number`; pass `capture_io: true` to also record arguments and the return value.

## License

Released under the [MIT License](LICENSE).