https://docs.spring.io/spring-boot/docs/current/reference/html/production-ready-metrics.html

https://github.com/spring-projects/spring-boot/tree/master/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics

The old MetricRepository and its InMemoryMetricRepository implementation are not used by default if you are on Java 8 or if you are using Dropwizard metrics.