An Unwired Server cluster provides highly available services to remote-device clients, typically requiring one or more relay servers and an optional load balancer.
When you install Sybase Unwired Platform, a cluster is created automatically, and Unwired Server is added to it. If you are installing the current version on a host that already has a previous version of Unwired Platform installed, the installer allows you to specify a new cluster name to avoid a conflict that might occur when the automatically selected name is used.
By default, a cluster name is the name of the first machine on which you install Unwired Platform. Consequently, each server can be a member of only one cluster. Cluster-configuration properties are saved in the cluster database.
For high availability, at least two servers must be defined for a cluster. However, to create a load-balanced system, many clients then also use a relay server. Without a relay server, clients require custom logic to determine which Unwired Server will directly receive requests. However, a relay-server free environment is not a highly available environment, nor can requests be distributed equally across multiple servers. Consequently, Sybase recommends that you always use a relay server.