How to use extensions in OpenTelemetry java for auto-instrumentation

Question

I have created a my custom extension with below custom spanProcessor with customizerProvider. I am providing my custom span processor in my tracerProvider.

I am running my extensions and java-agent with below cmd:

java -javaagent:C:/Users/abc/Desktop/auto-instrumentation/src/opentelemetry-javaagent.jar \
-Dotel.javaagent.extensions=C:/Users/abc/Desktop/auto-instrumentation/src/extension_example-1.0-SNAPSHOT.jar \
-Dotel.exporter.jaeger.endpoint=http://localhost:4317 \
-Dotel.traces.exporter=otlp \
-Dotel.metrics.exporter=none \
-Dotel.resource.attributes="service.name=MyApp" \
-jar MyApp-0.0.1-SNAPSHOT.jar \

my jaeger backend is not showing my spanProcessor attribute. It is only showing default span attributes. I even don't see any indication that my extension is loaded. can any body help me?

SpanProcessor class:

package org.example.javaagent;

import io.opentelemetry.context.Context;
import io.opentelemetry.sdk.common.CompletableResultCode;
import io.opentelemetry.sdk.trace.ReadWriteSpan;
import io.opentelemetry.sdk.trace.ReadableSpan;
import io.opentelemetry.sdk.trace.SpanProcessor;

public class ExampleSpanProcessor implements SpanProcessor {
    
    @Override
        public void onStart(Context parentContext, ReadWriteSpan span) {
            span.setAttribute("customAttribute", "customValue");
        }

        @Override
        public boolean isStartRequired() {
            return true;
        }

        @Override
        public void onEnd(ReadableSpan span) {}

        @Override
        public boolean isEndRequired() {
            return false;
        }

        @Override
        public CompletableResultCode shutdown() {
            return CompletableResultCode.ofSuccess();
        }

        @Override
        public CompletableResultCode forceFlush() {
            return CompletableResultCode.ofSuccess();
        }
}

CustomizerProvider class:

package org.example.javaagent;

import com.google.auto.service.AutoService;
import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizer;
import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizerProvider;
import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
import io.opentelemetry.sdk.trace.SdkTracerProviderBuilder;
import io.opentelemetry.sdk.trace.SpanLimits;

import java.util.HashMap;
import java.util.Map;

@AutoService(AutoConfigurationCustomizerProvider.class)
public class ExampleAutoConfigurationCustomizerProvider implements AutoConfigurationCustomizerProvider {

    @Override
    public void customize(AutoConfigurationCustomizer autoConfiguration) {
        System.out.printf("Called customize extension method");

        autoConfiguration
                .addTracerProviderCustomizer(this::configureSdkTracerProvider)
                .addPropertiesSupplier(this::getDefaultProperties);
    }

    private SdkTracerProviderBuilder configureSdkTracerProvider(
            SdkTracerProviderBuilder tracerProvider, ConfigProperties config) {

        return tracerProvider
                .setSpanLimits(SpanLimits.builder().setMaxNumberOfAttributes(1024).build())
                .addSpanProcessor(new ExampleSpanProcessor());
    }

    private Map<String, String> getDefaultProperties() {
        Map<String, String> properties = new HashMap<>();
        properties.put("otel.exporter.otlp.endpoint", "http://backend:8080");
        properties.put("otel.exporter.otlp.insecure", "true");
        properties.put("otel.config.max.attrs", "16");
        return properties;
    }
}

I hit the http://localhost:8080/myapp, but it is showing span which was collectedby javaagent and not my custome span which is customeAttribute: customeValue. It is not showing my print statement in console that my extension is called. So How do I get to know whether my extension is executed or not

Answer 1

As already said in the comment, https://github.com/open-telemetry/opentelemetry-java-instrumentation/tree/main/examples/extension is the right starting point to create an extension.

• it doesn't matter if you use gradle or maven
• @AutoService takes case of creating the lookup file using an annotation processor - maybe this was missing - but it's totally fine to just create the lookup file manually