Elastic APM Java agent - Custom metrics in plugins

ExampleMetricsInstrumentation.java

package co.elastic.apm.example.webserver.plugin;

import co.elastic.apm.agent.sdk.ElasticApmInstrumentation;
import io.micrometer.core.instrument.Metrics;
import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
import net.bytebuddy.asm.Advice;
import net.bytebuddy.description.method.MethodDescription;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.matcher.ElementMatcher;

import java.util.Collection;
import java.util.Collections;

import static net.bytebuddy.matcher.ElementMatchers.named;
import static net.bytebuddy.matcher.ElementMatchers.takesArgument;
import static net.bytebuddy.matcher.ElementMatchers.takesArguments;

public class ExampleMetricsInstrumentation extends ElasticApmInstrumentation {
    //For detailed documentation of these 3 methods, see the
    // package adjacent ExampleHttpServerInstrumentation class
    @Override
    public ElementMatcher<? super TypeDescription> getTypeMatcher() {
        return named("org.test.MyClass");
    }

    @Override
    public ElementMatcher<? super MethodDescription> getMethodMatcher() {
        return named("myMethod");
    }

    @Override
    public Collection<String> getInstrumentationGroupNames() {
        return Collections.singletonList("elastic-plugin-example");
    }

    public static class AdviceClass {
        private static volatile boolean metricWasAdded = false;
        @Advice.OnMethodEnter(suppress = Throwable.class, inline = false)
        public static void onEnterHandle() {
            if (!metricWasAdded) {
                Metrics.addRegistry(new SimpleMeterRegistry(new SimpleConfig() {

                    @Override
                    public CountingMode mode() {
                        // to report the delta since the last report
                        // this makes building dashboards a bit easier
                        return CountingMode.STEP;
                    }

                    @Override
                    public Duration step() {
                        // the duration should match metrics_interval, which defaults to 30s
                        return Duration.ofSeconds(30);
                    }

                    @Override
                    public String get(String key) {
                        return null;
                    }
                }, Clock.SYSTEM));
                metricWasAdded = true;
            }
            Metrics.counter("page_counter").increment();
        }
    }
}

pom.xml

...
    <dependencies>
        ...
        <dependency>
            <groupId>io.micrometer</groupId>
            <artifactId>micrometer-core</artifactId>
            <version>1.9.0</version>
            <exclusions>
                <exclusion>
                    <groupId>org.hdrhistogram</groupId>
                    <artifactId>HdrHistogram</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        ...
    </dependencies>
...