README.adoc

Minimal example on how to setup Spring Boot with Prometheus

What to expect

Run a Spring Boot application an read metrics from JVM and annotated application methods using a Prometheus endpoint.

Motivation

This is a working example for a minimal Spring-Boot 2.0.x app using Micrometer.io.

How to Run

To run with maven

mvn compile spring-boot:run

Open http://localhost:8080 to issue calls to be counted and to access the metrics.

Key bits and pieces

1. Add Micrometer to the projects. Add Actuator starter to let the autoconfiguration create a Prometheus metrics endpoint.

   pom.xml

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

2. Configure some specifics

   MetricsApplicationConfig.java

   @Configuration
   public class MetricsApplicationConfig {
   
       // as of now, this aspect needs to be created manually, see
       // https://github.com/micrometer-metrics/micrometer/issues/361
       @Bean
       public TimedAspect timedAspect(MeterRegistry registry) {
           return new TimedAspect(registry);
       }
   
       public MetricsApplicationConfig(PrometheusMeterRegistry prometheusMeterRegistry) {
           // add existing Prometheus modules as needed
           new MemoryPoolsExports().register(prometheusMeterRegistry.getPrometheusRegistry());
           new GarbageCollectorExports().register(prometheusMeterRegistry.getPrometheusRegistry());
           new VersionInfoExports().register(prometheusMeterRegistry.getPrometheusRegistry());
       }
   
   }

3. Collect application metrics at specific methods

   RestEndpoint.java

   @GetMapping("/countedCall")
   @Timed(histogram = true) // customize this to use a histogram
   public String countedCall() throws InterruptedException {
       /* ... */
       return "waited: " + delay + " ms";
   }

   ServiceClass.java

   @Timed(value = "doSomething", description = "this is doing something")
   public void doSomething() {
       log.info("hi");
   }