Custom-Sampler isn’t being applied

[bala-mane]

**I'm currently in the process of setting up the Otel SDK for our Ruby application. As part of this instrumentation, I've decided to use a custom sampler called TraceIdRatioBasedSampler. However, I'm encountering an issue where it appears that the sampler isn’t being applied correctly.

Has anyone else faced a similar issue or can suggest potential reasons why it's not working as expected? Any help or insights would be greatly appreciated!**

Below is the sample code.

require 'opentelemetry/sdk'
require 'opentelemetry/exporter/otlp'
require 'opentelemetry/instrumentation/all'

class TraceIdRatioBasedSampler
  def initialize(trace_id_ratio)
    @trace_id_ratio = trace_id_ratio
  end

  def should_sample?(trace_id:, parent_context:, links:, name:, kind:, attributes:)
    tracestate = OpenTelemetry::Trace.current_span(parent_context).context.tracestate
    decision = rand <= @trace_id_ratio ? OpenTelemetry::SDK::Trace::Samplers::Decision::RECORD_AND_SAMPLE : 
                                             OpenTelemetry::SDK::Trace::Samplers::Decision::DROP
    OpenTelemetry::SDK::Trace::Samplers::Result.new(decision: decision, attributes: {}, tracestate: tracestate)
  end

  def description
    'TraceIdRatioBasedSampler'
  end
end

trace_id_ratio = 0.5

sampler = TraceIdRatioBasedSampler.new(trace_id_ratio)
tracer_provider = OpenTelemetry::SDK::Trace::TracerProvider.new(sampler: sampler)
OpenTelemetry.tracer_provider = tracer_provider


OpenTelemetry::SDK.configure do |c|
   c.use 'OpenTelemetry::Instrumentation::Rails'
   c.resource = OpenTelemetry::SDK::Resources::Resource.create(
   'service.name' => 'RUBY-OTEL-SERVICE',
   'service.version' => '1.1'
   )

  c.add_span_processor(
    OpenTelemetry::SDK::Trace::Export::SimpleSpanProcessor.new(
      OpenTelemetry::SDK::Trace::Export::ConsoleSpanExporter.new
    )
  )

end

Tracer = OpenTelemetry.tracer_provider.tracer('run-app', '0.1.0')
span = Tracer.start_span('health-check-span')
begin
  span.set_attribute('health', 'Good')
ensure
  span.finish
end

[tnolet]

I'm seeing the same problem. I'm unable to use a custom sampler. This is the code used. It aims to do the same as the Node.js snippet I pasted below it.

# config/initializers/instrumentation.rb

require 'opentelemetry/sdk'
require 'opentelemetry/instrumentation/all'

class ChecklySampler
    def initialize
        puts("initializing ChecklySampler")
    end
    def should_sample?(trace_id:, parent_context:, links:, name:, kind:, attributes:)
      puts("using ChecklySampler")
      tracestate = OpenTelemetry::Trace.current_span(parent_context).context.tracestate
      decision = tracestate.get('checkly') ? OpenTelemetry::SDK::Trace::Samplers::Decision::RECORD_AND_SAMPLE : 
        OpenTelemetry::SDK::Trace::Samplers::Decision::DROP
      OpenTelemetry::SDK::Trace::Samplers::Result.new(decision: decision, attributes: {}, tracestate: tracestate)
    end
  
    def description
      'ChecklySampler'
    end
  end
  
checkly_sampler = ChecklySampler.new
tracer_provider = OpenTelemetry::SDK::Trace::TracerProvider.new(sampler: checkly_sampler)
OpenTelemetry.tracer_provider = tracer_provider


OpenTelemetry::SDK.configure do |c|
  c.service_name = 'dice'
  c.use_all()
end

Similar sampler but in Node.js that works fine.

const { NodeSDK } = require('@opentelemetry/sdk-node')
const { OTLPTraceExporter } = require('@opentelemetry/exporter-trace-otlp-proto')
const { getNodeAutoInstrumentations } = require('@opentelemetry/auto-instrumentations-node')
const { BatchSpanProcessor, SamplingDecision } = require('@opentelemetry/sdk-trace-base')
const { trace } = require('@opentelemetry/api')

const exporter = new OTLPTraceExporter({
  timeoutMillis: 2000,
})

const sdk = new NodeSDK({
  instrumentations: [getNodeAutoInstrumentations()],
  spanProcessors: new BatchSpanProcessor(exporter),
  sampler: {
    shouldSample: (context, traceId, spanName, spanKind, attributes, links) => {
      const isChecklySpan = trace.getSpan(context)?.spanContext()?.traceState?.get('checkly')
      if (isChecklySpan) {
        return { decision: SamplingDecision.RECORD_AND_SAMPLED }
      } else {
        return { decision: SamplingDecision.NOT_RECORD }
      }
    },
  },
})

[robertlaurin]

Instead of this

checkly_sampler = ChecklySampler.new
tracer_provider = OpenTelemetry::SDK::Trace::TracerProvider.new(sampler: checkly_sampler)
OpenTelemetry.tracer_provider = tracer_provider


OpenTelemetry::SDK.configure do |c|
  c.service_name = 'dice'
  c.use_all()
end

Try this

OpenTelemetry::SDK.configure do |c|
  c.service_name = 'dice'
  c.use_all()
end

OpenTelemetry.tracer_provider.sampler = ChecklySampler.new

[tnolet]

This works, thanks @robertlaurin . You can mark this as answered.

[dmathieu]

This seems like a bug? Shouldn't the sampler be settable when initializing a tracer provider?

[arielvalentin]

If you set it before initializing the SDK then The sampler is being assigned to the proxy tracer provider not the initialized SDK provider.

I'd argue this is something that should be a feature and the configurator should have the same/similar functionality provided but the OTel configuration file but in ruby dsl form.

I other words, we should initialize custom samplers and inject them into the configurator and have it inject it into the tracer provider as part of configure.

[tnolet]

I was indeed looking for a method in the configurator to configure the Sampler. From a user perspective that made the most sense to me.