With JK 1.2.x, new load-balancing and fault-tolerant support has been added via 2 new properties, redirect and activation.

Let's take an example environment:

A cluster with two nodes (worker1+worker2), running a webserver + tomcat tandem on each node and a loadbalancer in front of the nodes.

  # The advanced router LB worker
  worker.list=router

  # Define a worker using ajp13
  worker.worker1.port=8009
  worker.worker1.host=node1.domain.org
  worker.worker1.type=ajp13
  worker.worker1.lbfactor=1
  # Define prefered failover node for worker1
  worker.worker1.redirect=worker2

  # Define another worker using ajp13
  worker.worker2.port=8009
  worker.worker2.host=node2.domain.org
  worker.worker2.type=ajp13
  worker.worker2.lbfactor=1
  # Disable worker2 for all requests except failover
  worker.worker2.activation=disabled
  
  # Define the LB worker
  worker.router.type=lb
  worker.router.balance_workers=worker1,worker2

The redirect flag on worker1 tells the lb_worker to redirect the requests to worker2 only if worker1 is in error state. In other cases worker2 will not receive any requests, thus acting like a hot standby.