The services that comprise a GSLB pool (for example, VS-B3 and VS-B4 as shown in the following figures) are called GSLB pool members.

The following parameters can be used to specify members:

  • The virtual service.

  • An IP address, to specify standalone servers or VIPs defined by third-party load balancers

  • FQDN (Avi Load Balancer resolves the name to an IP for health-checks, and responds with a CNAME).

GSLB Pool Member Weights

All members of a GSLB pool share the same priority, but each member might have different weights. When a pool is selected, and its load is distributed across the members through the round-robin algorithm, the weights will dictate the fraction directed to each member. In the example depicted below, if VS-B3 and VS-B4 are healthy and can accept the load, GslbPool_3’s higher priority will direct all load to it, but weights will cause Avi Load Balancer to direct 40 percent of that load to VS-B3 and 60 percent to VS-B4.

There are different GSLB algorithms that can be configured to load balance the traffic to GSLB pool members. For more information, see Load Balancing Algorithms for GSLB.

Two-level GSLB Pool Member Service Selection

Selection of a GSLB pool member service is a two-level process:

  • Select the pool.

  • Select the service.

Within a GSLB service, each GSLB pool is given a distinct priority. A GSLB service allows for the assignment of the same priority to multiple GSLB pools. If a set of pools share a priority that exceeds the priorities of the other pools, the Avi Load Balancer selects from that set in a round-robin fashion, for the time, the minimum member logic is satisfied. The valid priority range includes a priority of zero. Setting a pool’s priority to zero disqualifies it from the selection. This might be done temporarily, for example, to perform maintenance on the services comprising the pool.

Note:

Setting pool priority to zero is not equivalent to deactivating it. A zero-priority pool will continue to be health monitored and its state will be displayed as UP, DOWN, or NOT DISABLED.