# Erlang/Elixir

Erlang and Elixir services send traces to Kopai through the OpenTelemetry SDK and OTLP exporter. The Kopai skills let your agent do the wiring.

Instrument your Erlang and Elixir applications to send traces, logs, and metrics to Kopai.

## Installation (Elixir)

Add to your `mix.exs`:

```elixir
defp deps do
  [
    {:opentelemetry_api, "~> 1.5"},
    {:opentelemetry, "~> 1.7"},
    {:opentelemetry_exporter, "~> 1.10"},
    {:opentelemetry_cowboy, "~> 1.0"}  # for auto HTTP instrumentation
  ]
end
```

## Installation (Erlang)

Add to your `rebar.config`:

```erlang
{deps, [
    {opentelemetry_api, "~> 1.5"},
    {opentelemetry, "~> 1.7"},
    {opentelemetry_exporter, "~> 1.10"}
]}.
```

## Configuration (Elixir)

```elixir
# config/runtime.exs
config :opentelemetry,
  span_processor: :batch,
  traces_exporter: :otlp

config :opentelemetry_exporter,
  otlp_protocol: :http_protobuf,
  otlp_endpoint: System.get_env("OTEL_EXPORTER_OTLP_ENDPOINT")
```

## Creating Spans

```elixir
# In your application module
defmodule MyApp.Application do
  use Application
  require OpenTelemetry.Tracer, as: Tracer

  def start(_type, _args) do
    # Initialize auto-instrumentation for Cowboy
    :opentelemetry_cowboy.setup()

    children = [
      # your supervision tree
    ]
    Supervisor.start_link(children, strategy: :one_for_one)
  end
end

# In your handler modules
defmodule MyApp.Handler do
  require OpenTelemetry.Tracer, as: Tracer

  def handle_request do
    Tracer.with_span "process_request" do
      Tracer.set_attributes([
        {"http.method", "GET"},
        {"custom.attribute", "value"}
      ])
      # ... your code
    end
  end
end
```

## Running Your Application

Set the required environment variables and run:

```bash
export OTEL_EXPORTER_OTLP_ENDPOINT="https://otlp-http.kopai.app"
export OTEL_SERVICE_NAME="my-service"
mix run --no-halt
```

| Variable | Description |
|----------|-------------|
| `OTEL_EXPORTER_OTLP_ENDPOINT` | Kopai OTLP endpoint |
| `OTEL_SERVICE_NAME` | Name shown in Kopai UI |

## Working Example

For a complete working example:

**[Erlang Example](https://github.com/kopai-app/kopai-integration-examples/tree/main/erlang)**