Configurable Health Indicator to observe HTTP Endpoints

I would like to have a generic health indicator to observe the availability of an HTTP endpoint, provided by another service.

Why do I see the need for such an implementation? At my clients I see a wide use of Spring Boot Admin as central service to monitor Spring Boot based applications. Often a service is shown there as healthy, but it isn't healthy (I am aware of the difference of liveness and readyness) as an REST-Endpoint or any other HTTP endpoint is not available or reachable. Although they have also other monitoring solutions running, mostly it is much easier to add an health indicator in a Spring Boot application than to get another department to do it.

I have written such an health indicator over the last years many times and I would be happy to contribute it, if I get some advices how to implement it in such a way, that it fits at best to the actuator framework in Spring Boot under the aspects of architecture and maintainability.

Start by reviewing the Spring Boot Actuator health indicator framework and the discussion on this issue. Define how a configurable indicator should observe external HTTP endpoints and fit the existing architecture; done means the proposed behavior and maintainable integration are agreed and implemented with verification.