The scalable data service enables application instances to run on multiple nodes simultaneously. Scalable services use two resource groups. The scalable resource group contains the application resources and the failover resource group contains the network resources (shared addresses) on which the scalable service depends. The scalable resource group can be online on multiple nodes, so multiple instances of the service can be running simultaneously. The failover resource group that hosts the shared address is online on only one node at a time. All nodes that host a scalable service use the same shared address to host the service.
The cluster receives service requests through a single network interface (the global interface). These requests are distributed to the nodes, based on one of several predefined algorithms that are set by the load-balancing policy. The cluster can use the load-balancing policy to balance the service load between several nodes.