Monitoring Jenkins

Jenkins installs "ping thread" on every remoting connection, such as controller/agent connections, regardless of its transport mechanism (such as SSH, JNLP, etc.). The lower level of the Jenkins remoting protocol is a message oriented protocol, and a ping thread periodically sends a ping message that the receiving end will reply. The ping thread measures the time it takes for the reply to arrive, and if it’s taking excessive time (currently 4 minutes and configurable), then it assumes that the connection was lost and initiates the formal close down.

This is to avoid an infinite hang, as some of the failure modes in network cannot be detected otherwise. The timeout is also set to a long enough value so that a temporary surge in the load or a long garbage collection pause will not trip off the close down.

Ping thread is installed on both controller & agent; each side pings the other and tries to detect the problem from their own sides.

The ping thread time out is reported through java.util.logging. In addition, the controller will also report this exception in the agent launch log. Note that some agent launchers, most notably SSH agents, writes all stdout/stderr outputs from the agent JVM into this same log file, so you need to be careful. See JENKINS-25695.

Sometimes, for example to diagnose the agent connection loss problem, you may want to disable the ping thread. This needs to be done in two places.

Disable the controller from pinging agents by setting hudson.slaves.ChannelPinger.pingIntervalSeconds on the controller JVM to -1.

You can also change the value in memory for a running Jenkins, if you don’t want to restart Jenkins.

Set pingIntervalSeconds and pingTimeoutSeconds on the controller JVM to -1:

To disable agents from pinging the controller, the system property

needs to be set to agents. How to do this depends on the launcher.