Telemetry Alarming service overview¶
The Telemetry Alarming services trigger alarms when the collected metering or event data break the defined rules.
The Telemetry Alarming service consists of the following components:
- An API server (aodh-api)
- Runs on one or more central management servers to provide access to the alarm information stored in the data store. 
- An alarm evaluator (aodh-evaluator)
- Runs on one or more central management servers to determine when alarms fire due to the associated statistic trend crossing a threshold over a sliding time window. 
- A notification listener (aodh-listener)
- Runs on a central management server and determines when to fire alarms. The alarms are generated based on defined rules against events, which are captured by the Telemetry Data Collection service’s notification agents. 
- An alarm notifier (aodh-notifier)
- Runs on one or more central management servers to allow alarms to be set based on the threshold evaluation for a collection of samples. 
These services communicate by using the OpenStack messaging bus.
