Using the Java Client Library for Prometheus

1. Log in to the Prometheus server.

2. Change the directory to the root directory for the Java project:

cd /home/cloud_user/content-prometheusdd-limedrop-svc

3. Run the project to verify that it is able to compile and run before making any changes:

./gradlew clean bootRun

4. Once you see the text Started App in X seconds, the application is running. Use control + c to stop it.

5. Edit build.gradle:

vi build.gradle

6. Locate the dependencies block and add the Prometheus client library dependencies:

dependencies {
  implementation 'io.prometheus:simpleclient:0.8.1'
  implementation 'io.prometheus:simpleclient_httpserver:0.8.1'

  ...

}

7. If you want, you can run the project again to automatically download the dependencies and make sure it still works:

./gradlew clean bootRun

1. Edit the controller class:

vi src/main/java/com/limedrop/svc/LimeDropController.java

2. Add the requested counter and gauge metrics:

package com.limedrop.svc;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import io.prometheus.client.Counter;
import io.prometheus.client.Gauge;

@RestController
public class LimeDropController {

    static final Counter totalRequests = Counter.build()
      .name("total_requests").help("Total requests.").register();
    static final Gauge inprogressRequests = Gauge.build()
      .name("inprogress_requests").help("Inprogress requests.").register();

    @GetMapping(path="/limesAvailable", produces = "application/json")
    public String checkAvailability() {
        inprogressRequests.inc();
        totalRequests.inc();

        String response = "{\"warehouse_1\": \"58534\", \"warehouse_2\": \"72399\"}";

        inprogressRequests.dec();
        return response;
    }

}

3. Run the application again to make sure it compiles:

./gradlew clean bootRun

1. Edit the main application class:

vi src/main/java/com/limedrop/svc/App.java

2. Use the Prometheus HTTPServer to set up a scrape endpoint on port 8081:

package com.limedrop.svc;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import io.prometheus.client.exporter.HTTPServer;
import java.io.IOException;

@SpringBootApplication
public class App {

	public static void main(String[] args) {
		SpringApplication.run(App.class, args);

                try {
                    HTTPServer server = new HTTPServer(8081);
                } catch (IOException e) {
                    e.printStackTrace();
                }
	}

}

3. Rerun the application to make sure it compiles:

./gradlew clean bootRun

While the application is still running, you should be able to access the /limesAvailable endpoint at http://<Prometheus Server Public IP>:8080. You can view the metrics at http://<Prometheus Server Public IP>:8081/metrics.

You should be able to access the /limesAvailable endpoint and see the total_requests counter increase each time you access the endpoint.

1. Edit the Prometheus config:

sudo vi /etc/prometheus/prometheus.yml

2. Add a scrape config to scrape metrics for your app:

scrape_configs:

  ...

  - job_name: 'LimeDrop Java Svc'
    static_configs:
    - targets: ['localhost:8081']

3. Restart Prometheus to reload the config:

sudo systemctl restart prometheus

4. Run your Java app and leave it running to allow Prometheus to collect metrics:

./gradlew clean bootRun

5. Access Prometheus in a browser at http://<Prometheus Server Public IP>:9090. Run queries to see the metrics you are collecting for your Java app:

total_requests

inprogress_requests