Metrics

When running applications in production we need to send monitoring information to some services like Prometheus.

Quarkus provides JVM and other statistics out-of-box with the Metrics extension, but it’s very valuable for our application to produce its own metrics. Let’s see how we can achieve it in this chapter.

Add the Metrics extension

Just open a new terminal window, and make sure you’re at the root of your tutorial-app project, then run:

Maven
Quarkus CLI

mvn quarkus:add-extension -Dextensions=quarkus-micrometer

quarkus extension add quarkus-micrometer

You should also add the quarkus-micrometer-registry-prometheus extension :

Maven
Quarkus CLI

mvn quarkus:add-extension -Dextensions=quarkus-micrometer-registry-prometheus

quarkus extension add quarkus-micrometer-registry-prometheus

Create TimeResource

Create a new TimeResource Java class in src/main/java in the com.redhat.developers package with the following contents:

package com.redhat.developers;
import java.time.Instant;
import java.util.Calendar;
import java.util.TimeZone;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

import io.micrometer.core.annotation.Counted;
import io.micrometer.core.instrument.MeterRegistry;

@Path("/time")
public class TimeResource {

    private final MeterRegistry registry; (1)

    TimeResource(MeterRegistry registry) {
        this.registry = registry;
        registry.gauge("offsetFromUTC", this,
        TimeResource::offsetFromUTC);(2)
    }

    @Counted(value = "time.now") (3)
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public Instant now() {
        return Instant.now();
    }

    int offsetFromUTC() {
        return TimeZone.getDefault().getOffset(Calendar.ZONE_OFFSET)/(3600*1000);
    }
}

1	Meters in Micrometer are created from and contained in a MeterRegistry.
2	Add a gauge that returns a value computed by our application.
3	The `@Counted` annotation allows the Metrics extension to count the number of invocations to this method.

Invoke the endpoint multiple times

We need to send some requests to our endpoint to increment our @Counted metrics, so use the following command:

for i in {1..5}; do curl -w '\n' localhost:8080/time; done

2020-05-12T22:38:10.546500Z
2020-05-12T22:38:10.869378Z
2020-05-12T22:38:11.188782Z
2020-05-12T22:38:11.510367Z
2020-05-12T22:38:11.832583Z

Check the metrics

By default the metrics are exposed in Prometheus format. You can check the output by pointing your browser to http://localhost:8080/q/metrics