A few days ago a few colleagues contacted me about my article on proactive application monitoring. They're building some templates for monitoring applications in the cloud and they had some questions specifically around thresholds for many of the metrics I had listed. For example, one of the questions was around datasource connection pool utilization. Is it reasonable to set thresholds for warnings if the connection pool was 85% utilized and critical if it was 95% utilized? Likewise, similar questions around CPU utilization and would a warning at 75% and critical alerts at 90% be reasonable?
The answer is, (drum roll please) it depends.
No two applications are alike. There are low volume, rarely used applications that may never get above 2% connection pool utilization. Conversely, there are high volume applications where the connection pool can be running at 90-100% utilization. Better metrics to watch (via the PMI metrics) are (a) how many threads had to wait for a connection from the connection pool and (b) how long those threads had to wait. Both of those metrics directly impact the throughput and response time of the application.
Same with CPU utilization. Some organizations like to run their servers hot over 90% utilization because they have spare, passive capacity they can bring online. Others like to run at less than 50% utilization because they want to have spare capacity in an active-active modus operandi.
Setting useful thresholds depends on understanding the organization's Service Level Agreements (SLAs) and the application's Non Functional Requirements (NFRs).
