Jenkins slave cannot connect with master: Incorrect acknowledgement sequence

Question

After update of our Jenkins master installation to its latest LTS version 2.46.3 one of its slaves (Windows 7 machine, 32-bit) cannot connect with the master.

The er

Answer 1

Is the Jenkins master instance running behind a load balancer? I had the same issue when my instance was running behind an Application Load Balancer in AWS.

If so, then the acknowledgement sequence could get modified because of differing protocols in the Load balancer. JNLP requires TCP connection on port 50000 by default.

If your setup is on AWS, you could try creating a private hosted zone in Route53 with an Alias record for your Jenkins instance's private IP address.

For e.g: jenkins.example.com -> your Jenkins instance's private IP

Then, in Jenkins UI -> Manage Jenkins -> Configure System -> Manage nodes and clouds -> Configure clouds -> (under advanced settings)

Tunnel connection through : jenkins.example.com:50000

This avoids your slave agents to have to go through the load balancer to connect to the Jenkins Master.