Log

Two paths into OpenTelemetry Logs:

• Elixir's :logger bridge (most common) — every Logger.info/2 call becomes an OTel LogRecord.
• SDK API — emit a LogRecord directly. For library authors and instrumentation that wants full control over the record.

Quick start

# config/config.exs — attach the handler at boot
config :kernel,
  logger: [
    {:handler, :otel, Otel.LoggerHandler, %{
      config: %{scope_name: "my_app"}
    }}
  ]

require Logger
Logger.info("checkout completed", user_id: 42)

The SDK ships logs to http://localhost:4318/v1/logs by default. See Configuration to change endpoint, processor, or limits.

:logger bridge

The handler converts every :logger call into a LogRecord and forwards to the SDK. See Logger Handler for the full attribute mapping.

Plain message

require Logger

Logger.info("checkout completed")

Structured (recommended)

Pass metadata as keyword pairs; the bridge maps each non-reserved key to a LogRecord attribute.

Logger.info("checkout completed", user_id: 42, total: 99.95)

Map / report form is preserved as a structured body:

Logger.info(%{event: "upload", size: 1024})

Severity

:logger levels map to OTel SeverityNumber:

Logger.warning("retry exhausted", attempt: 5)
Logger.error("payment provider timeout")

Exceptions

Set crash_reason to attach the exception struct + a formatted stacktrace attribute to the LogRecord.

try do
  process_payment()
rescue
  e ->
    Logger.error("payment failed", crash_reason: {e, __STACKTRACE__})
    reraise e, __STACKTRACE__
end

Trace context auto-propagation

When Logger fires inside a with_span/4 block, the LogRecord automatically carries the active span's trace_id / span_id — no extra wiring needed.

SDK API

scope = %Otel.API.InstrumentationScope{name: "my_app", version: "1.0.0"}
logger = Otel.API.Logs.LoggerProvider.get_logger(scope)

String body

Otel.API.Logs.Logger.emit(logger, %Otel.API.Logs.LogRecord{
  body: "checkout completed",
  severity_number: 9,
  severity_text: "info",
  attributes: %{"user.id" => 42}
})

Structured (map) body

Otel.API.Logs.Logger.emit(logger, %Otel.API.Logs.LogRecord{
  body: %{"event" => "upload", "size" => 1024},
  severity_number: 9
})

Raw bytes body

Wrap binary in a {:bytes, _} tag so the OTLP encoder serializes it as bytes_value instead of trying UTF-8.

Otel.API.Logs.Logger.emit(logger, %Otel.API.Logs.LogRecord{
  body: {:bytes, <<0xCA, 0xFE, 0xBA, 0xBE>>},
  severity_number: 9
})

With trace context

The current span's IDs flow through automatically when the call site is inside a with_span/4 block — same rule as the :logger bridge.

Limits

Defaults: 128 attributes per LogRecord, no string-length truncation.

config :otel,
  logs: [
    log_record_limits: %{
      attribute_count_limit: 256,
      attribute_value_length_limit: 1024
    }
  ]

See Configuration §"Logs pillar" for processor, batch, and environment-variable knobs.