About Global Server Load Balancing

Global Server Load Balancing (GSLB) is a technique that manages how clients are connected to a particular geographic location when a service is hosted in multiple locations.

•In an "Active-Passive" (or Primary-Backup) configuration, one location is nominated as active for each service. The other locations are idle for that service. If the active location becomes unavailable, one of the passive locations becomes active and all clients are directed to it.

•In an "Active-Active" (or multiple Primary) configuration, all locations are used and clients are load-balanced between them based on location performance and proximity.

The primary purpose of a GSLB system is business continuity, to ensure that services are always available even when one or more service locations becomes unavailable.

A second purpose of GSLB is to improve the customer experience. In other words, the purpose is to load balance each user to the best location from a choice of several. The choice can be based on location performance and proximity, so that clients are directed to the location that is closest and is performing the best. With this capability, the client gets the best possible level of service.

GSLB Within the Traffic Manager

The Traffic Manager implements GSLB techniques as the Global Load Balancer (GLB) feature. The GLB feature causes the Traffic Manager to add location-awareness to DNS lookups performed by end-users, so that the result of the DNS lookup is dependent upon its source.

You can add GLB Services to any Virtual Server using the DNS protocol. When a DNS request is received at this Virtual Server, the Traffic Manager forwards the request to the associated Pool. This might be either the built in internal DNS server pool (see The Traffic Manager DNS Server) or it might be a pool of external DNS servers. With both of these options, you must configure the pool back ends to return multiple "A" records, containing all IP addresses for the domain names which are to be resolved, across all locations.

If the domain name resolved matches the domain name in a GLB Service attached to the Virtual Server, the Traffic Manager filters the list depending upon the GLB Service configuration, before returning to the end user only the IP address or IP addresses that are appropriate for the end user's location.

You can deploy the Traffic Manager in each GLB Location so it can monitor local performance and availability, although this is not necessary. All monitoring can be performed remotely should you require your Traffic Managers in some alternative location. Your Traffic Managers exchange monitoring information with their peers, regardless of their actual location, so that all Traffic Managers can work together to coordinate their operation.

A GLB Service only filters "A" records, not "AAAA" records. If the DNS response contains any "AAAA" records, the Traffic Manager passes the response through untouched.