When i configure my embedded Tomcat server with the default settings:

server.tomcat.threads.max=200

And start sending 400 HTTP calls simultaneously with JMeter, I see logs with worker threads > 200.

"thread":"http-nio-8100-exec-16"
"thread":"http-nio-8100-exec-263"
"thread":"http-nio-8100-exec-207"

After reducing the configuration to 100

server.tomcat.threads.max=100

I still see logs of worker threads > 100

"thread":"http-nio-8100-exec-13"
"thread":"http-nio-8100-exec-173"
"thread":"http-nio-8100-exec-107"

Strangely, when i configure the maximum amount of threads somewhere between to 1-15, the limit is respected and only logs appear within the limit:

Setting it to 1:

"thread":"http-nio-8100-exec-1"
"thread":"http-nio-8100-exec-1"
"thread":"http-nio-8100-exec-1"

Setting it to 15:

"thread":"http-nio-8100-exec-2"
"thread":"http-nio-8100-exec-14"
"thread":"http-nio-8100-exec-9"

I have not tried to find the tipping point between 15-100.

Furthermore, when running with 100-200 threads, the only way the limit is respected, is by also decreasing the server.tomcat.max-connections from the default 8192 to something low like 25.

I have difficulty in understanding this behavior.

• Why is a very low thread number respected
• Why is the default thread amount (or even another high number like 100) not respected until (extremely) decreasing the server.tomcat.max-connections.

Java 17 running on 2 cores in Kubernetes with dependencies:

|  +- org.springframework.boot:spring-boot-starter-web:jar:3.2.5:compile
|  |  +- org.springframework.boot:spring-boot-starter-tomcat:jar:3.2.5:compile
|  |  |  +- org.apache.tomcat.embed:tomcat-embed-core:jar:10.1.20:compile
|  |  |  - org.apache.tomcat.embed:tomcat-embed-websocket:jar:10.1.20:compile