# Erlang/Elixir

Instrument Erlang and Elixir applications with OpenTelemetry

# Integration

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:

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