FusionReactor on-premise has built-in alerting in the form of the crash protection feature.
Crash protection is able to alert you on potential issues and prevent a potential outage using its protection strategies.
The types of alert available are:
Quantity protection - to protect against a flood of requests
Timeout protection - to protect against a long-running request
Memory protection - to protect against a full heap memory
CPU protection - to protect against CPU starvation
You can find out more about crash protection in the documentation.