Assume that QB server running on port 7000.
Agent running on port 8000.
Currently, my QB server had some connection problem with agent and assigned builds were not processed with below error message.
com.caucho.hessian.client.HessianConnectionException: 500: java.net.SocketTimeoutException: Read timed out
Checked that if agent is blocking TCP on port 8000 or hanging, it may still can send heartbeat to server.
So agent.getLastPulse() will not work well.
Because of that this agent will not be set Inactive node.
I hope if it have anything block between agent and server, agent will not able to send heartbeat to server.

The command I run on agent to block on port 8000
iptables -A INPUT -p tcp --dport 8000 -j DROP