Managing HP Serviceguard for Linux, Sixth Edition, August 2006

Designing Highly Available Cluster Applications
Handling Application Failures
Appendix B 317
Be Able to Monitor Applications
All components in a system, including applications, should be able to be
monitored for their health. A monitor might be as simple as a display
command or as complicated as a SQL query. There must be a way to
ensure that the application is behaving correctly. If the application fails
and it is not detected automatically, it might take hours for a user to
determine the cause of the downtime and recover from it.