To ensure reliable operation of software it is necessary to monitor essential system parameters. This enhancement proposes the addition of well-known monitoring endpoints and metrics for each process adhering to the Eclipse MicroProfile standard.
This proposal does not talk about health checks. There is a separate specification for Health Checks.
In the previous release we mentioned our intent to investigate Micrometer. This has led to key changes in this specification, and the corresponding API, to allow for a variety of possible implementations. As examples, it should be possible to implement this specification using metrics libraries from Micrometer or Open Telemetry. The modifications to the API, since the previous release, have been made in consideration of maintaining backwards compatibility, as much as possible, but while removing parts of the API that limited the ability to plug in new implementations.
Reliable service of a platform needs monitoring. There is already JMX as standard to expose metrics, but remote-JMX is not easy to deal with and especially does not fit well in a polyglot environment where other services are not running on the JVM. To enable monitoring in an easy fashion it is necessary that all MicroProfile implementations follow a certain standard with respect to (base) API path, data types involved, always available metrics and return codes used.
Health checks are primarily targeted at a quick yes/no response to the question "Is my application still running ok?". Modern systems that schedule the starting of applications (e.g. Kubernetes) use this information to restart the application if the answer is 'no'.
Metrics on the other hand can help to determine the health. Beyond this they serve to pinpoint issues, provide long term trend data for capacity planning and pro-active discovery of issues (e.g. disk usage growing without bounds). Metrics can also help those scheduling systems decide when to scale the application to run on more or fewer machines.