Monitoring / Alerting when the aggregator fails to run

[chgeuer]

The Azure Marketplace Metering API requires ISVs to submit their usage data in due time; specifically, events which are more than 24 hours old are rejected by the API. Therefore, it is important that the aggregator must run 'often enough' to catch-up with events, so that all events in EventHub are processed and everything submittable is submitted.

The JSON files in the snapshot storage contain timestamps which indicate the sequence number and timestamp in a given partition until when all events have been aggregated. If that timestamp / sequence number indicates that the aggregator didn't run, an alarm should be raised.