After upgrading to spring-boot 2.5, CancelledServerWebExchangeException started to appear in prometheus http_server_requests_seconds metrics quite frequently (up to 10% server responses end up with it, according to graphics). It appears in my own API metrics, as well as actuator endpoints metrics (health, info, prometheus).
Example:
http_server_requests_seconds_count{exception="CancelledServerWebExchangeException",method="GET",outcome="UNKNOWN",status="200",uri="/actuator/health"} 137.0
Kind of strange combination of outcome="UNKNOWN" & status="200"
The problem is: all these requests have successful responses.
Questions: what is this exception for and why may it occur so often?
How to reproduce: start application locally and put some load on it (I used 50 threads in jmeter accessing actuator endpoints)