datadog opentelemetry example sampler for a Sinatra Ruby app

datadog_opentelemetry_example_sampler.rb

require 'opentelemetry/sdk'
require 'opentelemetry-instrumentation-sinatra'
require 'opentelemetry/exporter/otlp'

# Implements sampling based on a probability.
class DatadogTraceIdRatioBased < ::OpenTelemetry::SDK::Trace::Samplers::TraceIdRatioBased  
  def initialize(probability)
    @probability = probability
    super(probability)
  end
  # @api private
  #
  # See {Samplers}.
  def should_sample?(trace_id:, parent_context:, links:, name:, kind:, attributes:)
    tracestate = ::OpenTelemetry::Trace.current_span(parent_context).context.tracestate
    if sample?(trace_id)
      ::OpenTelemetry::SDK::Trace::Samplers::Result.new(decision: ::OpenTelemetry::SDK::Trace::Samplers::Decision::RECORD_AND_SAMPLE, attributes: {'_sample_rate' =>  @probability}, tracestate: tracestate)
    else
      ::OpenTelemetry::SDK::Trace::Samplers::Result.new(decision: ::OpenTelemetry::SDK::Trace::Samplers::Decision::RECORD_ONLY, attributes: {'_sample_rate' =>  @probability}, tracestate: tracestate)
    end
  end
end

OpenTelemetry::SDK.configure do |c|
  c.use 'OpenTelemetry::Instrumentation::Sinatra'

  c.add_span_processor(
    OpenTelemetry::SDK::Trace::Export::BatchSpanProcessor.new(
      OpenTelemetry::Exporter::OTLP::Exporter.new()
    )
  )
end

OpenTelemetry.tracer_provider.sampler = ::OpenTelemetry::SDK::Trace::Samplers.parent_based(root: DatadogTraceIdRatioBased.new(0.5))