Issue
Agent connections, or controller connections to an operations center using WebSocket transport are being dropped unexpectedly, and you see either of the following logs:
WARNING o.e.j.server.LowResourceMonitor#monitor: Low Resources: Check if the ThreadPool from monitored connectors are lowOnThreads and if all connections number is higher than the allowed maxConnection
WARNING o.e.j.server.LowResourceMonitor#monitor: Low Resources: Server low on threads: 200, idleThreads:0
Resolution
When the Jetty thread group is low on resources, there is a monitor that will cause the WebSocket timeout to become 1 second, which can cause WebSocket transport connections to be dropped (agent connections, or controller connections to an operations center).
There could be multiple reasons for this issue, so when this happens, please collect Required Data: CloudBees CI hang or high CPU on Kubernetes or Linux, and contact CloudBees Support.
CloudBees Support will review the thread dumps captured to understand what plugin or setting could be causing the low number of threads in the Jetty thread pool.