How should the components be set up for this environment?

A NetScaler cluster provides both high availability and horizontal scalability for a multi-site environment, allowing multiple NetScaler appliances to function as a single system to efficiently load balance and proxy traffic to internal StoreFront servers and Delivery Controllers. This setup ensures continuous service and improved performance by distributing the load across multiple appliances.

NetScaler high availability (HA) typically refers to an active-passive pair, which provides redundancy but not the same level of horizontal scalability and active-active traffic distribution as a cluster for a large, multi-site environment.

A back-up vServer is a specific configuration for a virtual server to redirect traffic in case of failure, not an overarching solution for setting up an entire environment with multiple components like StoreFront and Delivery Controllers.

GSLB is used for distributing client requests across multiple geographically dispersed datacenters, operating at a higher level than the internal load balancing of StoreFront and Delivery Controllers within a single datacenter provided by a NetScaler cluster.