Why Open Telemetry Java Agent Extension doesn't work

I’m trying to create an extension to the Otel Java Agent that will open a span for each method the flow goes through.

My Test Main:

package org.example;

import io.opentelemetry.api.GlobalOpenTelemetry;
import io.opentelemetry.api.trace.Span;
import io.opentelemetry.api.trace.Tracer;
import io.opentelemetry.context.Scope;
import io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporter;
import io.opentelemetry.sdk.OpenTelemetrySdk;
import io.opentelemetry.sdk.trace.SdkTracerProvider;
import io.opentelemetry.sdk.trace.export.BatchSpanProcessor;
import io.opentelemetry.sdk.trace.export.SpanExporter;

import java.time.Duration;

/**
 * @author David Dvash
 */

public class Main {

    public static void main(String[] args) throws InterruptedException {
        while (true) {
            System.out.println("Going to sleep");
            Thread.sleep(10000);
            printHello1("Hello");
        }
    }

    public static void printHello1(String name) {
        printHello2(name);
    }

    public static void printHello2(String name) {
        System.out.println("Hello, " + name);
    }

}

My extension classes:

package org.example;

import com.google.auto.service.AutoService;
import io.opentelemetry.javaagent.extension.instrumentation.InstrumentationModule;
import io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation;
import net.bytebuddy.matcher.ElementMatcher;
import net.bytebuddy.matcher.ElementMatchers;

import java.util.List;

import static java.util.Collections.singletonList;

/**
 * @author David Dvash
 */
@AutoService(InstrumentationModule.class)
public class AllMethodsInstrumentationModule extends InstrumentationModule {

    public AllMethodsInstrumentationModule() {
        super("otel-extension", "otelextension");
        System.out.println("In AllMethodsInstrumentationModule Constructor");
    }

    @Override
    public int order() {
        return 1;
    }

    @Override
    public List<String> getAdditionalHelperClassNames() {
        return List.of(AllMethodsInstrumentation.class.getName(),
                       "io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation",
                       MethodSpanAdvice.class.getName());
    }

    @Override
    public ElementMatcher.Junction<ClassLoader> classLoaderMatcher() {
        return ElementMatchers.any();
    }

    @Override
    public List<TypeInstrumentation> typeInstrumentations() {
        return singletonList(new AllMethodsInstrumentation());
    }
}

package org.example;

import com.google.auto.service.AutoService;
import io.opentelemetry.javaagent.extension.instrumentation.InstrumentationModule;
import io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation;
import io.opentelemetry.javaagent.extension.instrumentation.TypeTransformer;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.matcher.ElementMatcher;
import net.bytebuddy.matcher.ElementMatchers;


/**
 * @author David Dvash
 */
@AutoService(TypeInstrumentation.class)
public class AllMethodsInstrumentation implements TypeInstrumentation {

    @Override
    public ElementMatcher<ClassLoader> classLoaderOptimization() {
        System.out.println("in classLoaderOptimization");
            // Match all class loaders
            return ElementMatchers.any();
    }

    @Override
    public ElementMatcher<TypeDescription> typeMatcher() {
        System.out.println("in typeMatcher");
        // Match all classes
        return ElementMatchers.any();

    }

    @Override
    public void transform(TypeTransformer transformer) {
        System.out.println("in transform");
        transformer.applyAdviceToMethod(
            ElementMatchers.any(),
            MethodSpanAdvice.class.getName()
        );
    }
}

package org.example;

import io.opentelemetry.api.GlobalOpenTelemetry;
import io.opentelemetry.api.trace.Span;
import io.opentelemetry.api.trace.StatusCode;
import io.opentelemetry.api.trace.Tracer;
import io.opentelemetry.context.Scope;
import net.bytebuddy.asm.Advice;

/**
 * @author David Dvash
 */

public class MethodSpanAdvice {

    // This advice is added at the beginning of the instrumented method (OnMethodEnter).
    // It creates and starts a new span, and makes it active.
    @Advice.OnMethodEnter(suppress = Throwable.class)
    public static Scope onEnter(@Advice.Local("otelSpan") Span span) {
        // Get a Tracer instance from OpenTelemetry.
        Tracer tracer = GlobalOpenTelemetry.getTracer("instrumentation-library-name", "semver:1.0.0");
        System.out.print("Entering method");

        // Start a new span with the name "mySpan".
        span = tracer.spanBuilder("mySpan").startSpan();

        // Make this new span the current active span.
        Scope scope = span.makeCurrent();

        // Return the Scope instance. This will be used in the exit advice to end the span's scope.
        return scope;
    }

    // This advice is added at the end of the instrumented method (OnMethodExit).
    // It first closes the span's scope, then checks if any exception was thrown during the method's execution.
    // If an exception was thrown, it sets the span's status to ERROR and ends the span.
    // If no exception was thrown, it sets a custom attribute "wordCount" on the span, and ends the span.
    @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)
    public static void onExit(@Advice.Return(readOnly = false) int wordCount,
                              @Advice.Thrown Throwable throwable,
                              @Advice.Local("otelSpan") Span span,
                              @Advice.Enter Scope scope) {
        // Close the scope to end it.
        scope.close();

        // If an exception was thrown during the method's execution, set the span's status to ERROR.
        if (throwable != null) {
            span.setStatus(StatusCode.ERROR, "Exception thrown in method");
        } else {
            // If no exception was thrown, set a custom attribute "wordCount" on the span.
            span.setAttribute("wordCount", wordCount);
        }

        // End the span. This makes it ready to be exported to the configured exporter (e.g., Jaeger, Zipkin).
        span.end();
    }
}

The extension’s gradle.build:

plugins {
    id 'java'
}

group 'org.example'
version '1.0-SNAPSHOT'

repositories {
    mavenCentral()
}

dependencies {
    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.8.1'
    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.8.1'

    implementation group: 'net.bytebuddy', name: 'byte-buddy', version: '1.15.3'

    implementation group: 'io.opentelemetry', name: 'opentelemetry-api', version: '1.42.1'

    implementation 'io.opentelemetry.javaagent:opentelemetry-javaagent-extension-api:2.8.0-alpha'

    // https://mvnrepository.com/artifact/io.opentelemetry.javaagent/opentelemetry-javaagent-tooling
    implementation 'io.opentelemetry.javaagent:opentelemetry-javaagent-tooling:2.8.0-alpha'

    // https://mvnrepository.com/artifact/com.google.auto.service/auto-service
    implementation 'com.google.auto.service:auto-service:1.1.1
}

test {
    useJUnitPlatform()
}

The VM arguments I use in IntelliJ to run the agent and the extension: -javaagent:"F:\\views\\g\main_mono_new\\Qrelease\\3rd\\openTelemetry-javaAgent\\opentelemetry-javaagent.jar" -Dotel.javaagent.extensions="F:\\views\\OtelExtension\\build\\libs\\OtelExtension-1.0-SNAPSHOT.jar" -Dotel.service.name=test-service -Dotel.javaagent.debug=true

I know the agent works correctly because I added some manual traces and were able to see them In Grafana (using Tempo). However I don’t see any of the traces I expect to see from the extension. What is not correct with my extension?

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