Fails to change leadership when leader pod in configMap doesn't exist

[jaredstehler]

In the case where the leadership configMap references a non-existent pod (perhaps in the case of a cluster rolling upgrade?), the leadership controller gets into a state where it cannot update leader to a valid active pod.

This is due to the underlying fabric8 library's Readiness::isReady() throwing IllegalArgumentException when the queried item is null / missing. See: fabric8io/kubernetes-client#2672

Since this is resolved in fabric8 5.1+ and there seems to be a question of even continuing on with fabric8, it would seem that the simplest solution here would be to wrap Fabric8LeadershipController::isPodReady() with a try/catch and return false on IllegalArgument?

https://github.com/spring-cloud/spring-cloud-kubernetes/blob/main/spring-cloud-kubernetes-fabric8-leader/src/main/java/org/springframework/cloud/kubernetes/fabric8/leader/Fabric8LeadershipController.java#L131

[jaredstehler]

project has since moved fabric8 dep to 5.5.