Problem
On the PHP agent's APM Summary page, what is the PHP agent instance count in the Hosts table? Why do these numbers change, and why does there appear to be an inconsistency in them?
Cause
Each server listed on the Summary page includes the number of instances; for example, 42 app instances. The instance count indicates the maximum number of open file descriptors used by the PHP agent in the last reported harvest. These file descriptors are open I/O sockets and reflect the agent/daemon communication channels.
The number of instances will increase if command line, background, or external processes are running. The number also may be influenced by heavy throughput. For example, an Apache server may be configured to grow the connection pool to accommodate the increased load.
A difference in the expected values between servers may reflect background tasks being run on one server but not the other. An unexpected count also may indicate a misconfigured load balancer.