Monitoring Java Applications with Prometheus

Professional

You can instrument your Java application with the official Prometheus Java client library and let the Glouton agent scrape its /metrics endpoint.

Install the client library

Add the dependencies to your pom.xml (Maven):

<dependency>
  <groupId>io.prometheus</groupId>
  <artifactId>prometheus-metrics-core</artifactId>
  <version>1.3.6</version>
</dependency>
<dependency>
  <groupId>io.prometheus</groupId>
  <artifactId>prometheus-metrics-exporter-httpserver</artifactId>
  <version>1.3.6</version>
</dependency>

Minimal example

The snippet below defines a counter and exposes it on http://localhost:8080/metrics:

import io.prometheus.metrics.core.metrics.Counter;
import io.prometheus.metrics.exporter.httpserver.HTTPServer;

public class App {
    static final Counter requestsTotal = Counter.builder()
        .name("myapp_requests_total")
        .help("Total number of processed requests.")
        .register();

    public static void main(String[] args) throws Exception {
        HTTPServer server = HTTPServer.builder().port(8080).buildAndStart();
        requestsTotal.inc();
        Thread.currentThread().join();
    }
}

Scrape with Glouton

Configure Glouton to scrape your application by adding the following to /etc/glouton/conf.d/50-prometheus-metrics.conf:

metric:
  prometheus:
    targets:
      - url: "http://localhost:8080/metrics"
        name: "my_java_application"
        allow_metrics:
          - "myapp_requests_total"

Restart the agent to apply the configuration. See Prometheus Monitoring for the full list of options, including Docker label auto-discovery and Kubernetes annotations.