Add availability metric and alarms to API Gateway

[amodam-user]

Feature scope

API Gateway

Describe your suggested feature

Similar to TPS/fault count, API Gateway should offer the ability to metric and alarm on service availability. Specifically:

Measuring availability based on requests. For your service it may be easier to count successful and failed requests instead of “time available for use”.

can be done fairly easily with the following:

• add a metricAvailability to the API Gateway MetricFactory that computes 100 * (1 - (faults/count)). Both the fault and count metric(s) are already available within the existing metric factory.