[Hawkular-dev] availability as a computed metric (was availability and metric endpoints)

I think that there was some general consensus or at least convergence towards the notion that availability is a function that reports resource state change. It could be a function of metric data or something else. In RHQ, those functions were defined implicitly by and hard coded into plugins. There are a couple of important implications with this. First, users cannot easily determine how availability is computed for a particular resource type. Secondly, availability is computed by the agent and not by the server. I think we need to expand on what was done in RHQ. I think that availability functions should be explicit and stored in inventory so that users can easily see how availability is determined and also change how availability is computed should the need arise. The monitoring agent, not the server, should compute availability. I am using the term agent loosely here because it applies to agents that embedded in-process, agents that are co-located in a separate process, and agents that are remote possibly embedded in the hawkular server. There needs to be more done in terms of correlation. When there is a state change, we should be reporting an accompanying event, e.g., server shutdown, server restarted, etc. If we compute availability based on some metric, then maybe the event reported is something like, http status code is X or the response time is Y. - John