7.2 Introduction to Load Balancer High Availability

Being the entry point into your WebSphere system, it is extremely important that your Load Balancer is highly available. Otherwise, it would be a single point of failure.

While it is possible to use external clustering software (see Chapter 4, External clustering software) to monitor the Load Balancer node and provide failover to a backup node, IBM WebSphere Edge Components Load Balancer provides a built-in High Availability solution, which allows you to configure a backup Load Balancer server with exactly the same configuration. If the primary Load Balancer server fails, the backup server will take over the load balancing for all clusters.

The two Load Balancer servers need connectivity to the same clients and to the same cluster of servers, as well as connectivity between themselves. Both Load Balancer servers must be running the same operating systems, and they must be connected to the same network.

The two Load Balancer servers are referred to as the primary server and the backup (or standby) server. These are the roles that are associated with each server during the configuration.

Load Balancer servers run in a specific state: one server is active and the other server is in standby state. This means that the Load Balancer server that is in active state is the one that is distributing the workload.

The Load Balancer server that is in the standby state monitors the active one. If the active server fails, the standby server performs a failover. It switches to the active state, takes over the cluster IP alias, and starts load balancing the cluster. So the state of a server changes when a failure occurs, but the roles do not change during a failure.

A Load Balancer server can be the primary server for one Web server cluster while acting as standby for another cluster. If the primary Load Balancer of that other cluster is also the standby for the first cluster, the resulting configuration is called mutual High Availability.

However, it is not possible to have two primary servers for one cluster, both doing active load balancing at the same time (for example, an active/active configuration), as the virtual IP alias for the cluster can only be configured on one server in the network.

We describe how to set up High Availability for IBM WebSphere Edge Components Load Balancer in 11.3, Configure Load Balancer High Availability.

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