How Does NLB Cluster Convergence Work?
Convergence involves computing a new cluster membership list and recalculating the statistical mapping of client requests to the cluster hosts. There are two instances in which cluster traffic has to be remapped due to a change in cluster membership: when a host leaves the cluster and when a host joins the cluster. A convergence can also be initiated when several other events take place on a cluster, such as changing the load balancing weight on a host or implementing port rule changes. Removing a Member. Two situations cause a host to leave the cluster or go offline. First, the host can fail, an event that is detected by the NLB heartbeat. Second, a system administrator can explicitly remove a host out of the load-balancing cluster or stop NLB on that host. The NLB heartbeat. NLB uses a heartbeat mechanism to determine the state of the hosts that are load balanced. This message is an Ethernet-level broadcast that goes to every load-balanced cluster host. NLB assumes that a host is fun
