How to redirect Prometheus Metrics to the default spring boot server - spring-boot

Question

I am trying to expose a custom Gauge metric from my Spring Boot Application. I am using Micrometer with the Prometheus registry to do so. I have set up the PrometheusRegistry and configs as per - Micrometer Samples - Github but it creates one more HTTP server for exposing the Prometheus metrics. I need to redirect or expose all the metrics to the Spring boot's default context path - /actuator/prometheus instead of a new context path on a new port. I have implemented the following code so far -
PrometheusRegistry.java -
package com.xyz.abc.prometheus;
import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.time.Duration;
import com.sun.net.httpserver.HttpServer;
import io.micrometer.core.lang.Nullable;
import io.micrometer.prometheus.PrometheusConfig;
import io.micrometer.prometheus.PrometheusMeterRegistry;
public class PrometheusRegistry {
public static PrometheusMeterRegistry prometheus() {
PrometheusMeterRegistry prometheusRegistry = new PrometheusMeterRegistry(new PrometheusConfig() {
#Override
public Duration step() {
return Duration.ofSeconds(10);
}
#Override
#Nullable
public String get(String k) {
return null;
}
});
try {
HttpServer server = HttpServer.create(new InetSocketAddress(8081), 0);
server.createContext("/sample-data/prometheus", httpExchange -> {
String response = prometheusRegistry.scrape();
httpExchange.sendResponseHeaders(200, response.length());
OutputStream os = httpExchange.getResponseBody();
os.write(response.getBytes());
os.close();
});
new Thread(server::start).run();
} catch (IOException e) {
throw new RuntimeException(e);
}
return prometheusRegistry;
}
}
MicrometerConfig.java -
package com.xyz.abc.prometheus;
import io.micrometer.core.instrument.MeterRegistry;
public class MicrometerConfig {
public static MeterRegistry carMonitoringSystem() {
// Pick a monitoring system here to use in your samples.
return PrometheusRegistry.prometheus();
}
}
Code snippet where I am creating a custom Gauge metric. As of now, it's a simple REST API to test - (Please read the comments in between)
#SuppressWarnings({ "unchecked", "rawtypes" })
#RequestMapping(value = "/sampleApi", method= RequestMethod.GET)
#ResponseBody
//This Timed annotation is working fine and this metrics comes in /actuator/prometheus by default
#Timed(value = "car.healthcheck", description = "Time taken to return healthcheck")
public ResponseEntity healthCheck(){
MeterRegistry registry = MicrometerConfig.carMonitoringSystem();
AtomicLong n = new AtomicLong();
//Starting from here none of the Gauge metrics shows up in /actuator/prometheus path instead it goes to /sample-data/prometheus on port 8081 as configured.
registry.gauge("car.gauge.one", Tags.of("k", "v"), n);
registry.gauge("car.gauge.two", Tags.of("k", "v1"), n, n2 -> n2.get() - 1);
registry.gauge("car.help.gauge", 89);
//This thing never works! This gauge metrics never shows up in any URI configured
Gauge.builder("car.gauge.test", cpu)
.description("car.device.cpu")
.tags("customer", "demo")
.register(registry);
return new ResponseEntity("Car is working fine.", HttpStatus.OK);
}
I need all the metrics to show up inside - /actuator/prometheus instead of a new HTTP Server getting created. I know that I am explicitly creating a new HTTP Server so metrics are popping up there. Please let me know how to avoid creating a new HTTP Server and redirect all the prometheus metrics to the default path - /actuator/prometheus. Also if I use Gauge.builder to define a custom gauge metrics, it never works. Please explain how I can make that work also. Let me know where I am doing wrong.
Thank you.

Answer 1

Every time you call MicrometerConfig.carMonitoringSystem(); it is creating a new prometheus registry (and trying to start a new server)
You need to inject the MeterRegistry in your class that is creating the gauge and use the injected MeterRegistry that way.