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Learningpaths: Exposing Prometheus Metrics from Java

The Micrometer library is a popular way to expose
application metrics to a service like Prometheus.

Adding Dependencies

To add the Micrometer dependency for Prometheus with Maven:

<dependencies>
    <dependency>
        <groupId>io.micrometer</groupId>
        <artifactId>micrometer-registry-prometheus</artifactId>
        <version>${micrometer.version}</version>
    </dependency>
</dependencies>

If you’re using Gradle instead:

dependencies {
    implementation 'io.micrometer:micrometer-registry-prometheus:latest.release'
}

Dependencies

See the
releases page for
the latest version.

With the correct dependencies in place, you’re ready to expose metrics.

Exposing Metrics

For exposing application metrics, you have two options:

  • if you’re writing a Java application without using a framework, you must
    expose the endpoint yourself
  • if you’re using Spring Boot, you can ad the
    Spring Boot Actuator
    dependency to your application

Using Vanilla Java

The following example uses the JDK’s com.sun.net.httpserver.HttpServer to
expose a /prometheus endpoint. The PrometheusMeterRegistry contains a
scrape() function, which can supply the metric data to Prometheus. All you
need to do is wire the function to an endpoint.

PrometheusMeterRegistry prometheusRegistry =
    new PrometheusMeterRegistry(PrometheusConfig.DEFAULT);

try {
    HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
    server.createContext("/prometheus", httpExchange -> {
        String response = prometheusRegistry.scrape(); (1)
        httpExchange.sendResponseHeaders(200, response.getBytes().length);
        try (OutputStream os = httpExchange.getResponseBody()) {
            os.write(response.getBytes());
        }
    });

    new Thread(server::start).start();
} catch (IOException e) {
    throw new RuntimeException(e);
}

Using Spring Boot

First, update the scope and remove the version of the
micrometer-registry-prometheus dependency. Then add the
spring-boot-starter-actuator dependency to your project.

Maven:

<dependencies>
    <dependency>
        <groupId>io.micrometer</groupId>
        <artifactId>micrometer-registry-prometheus</artifactId>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-actuator</artifactId>
    </dependency>
</dependencies>

Gradle:

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    runtimeOnly 'io.micrometer:micrometer-registry-prometheus'
}

Next, enable the Prometheus actuator endpoint. At the time of writing, you must
add prometheus to the list of exposed Spring Boot Actuator endpoints. Your
endpoint configuration might look like the following:

management.endpoints.web.exposure.include: info, health, prometheus

This exposes metrics at the /actuator/prometheus endpoint.

References

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