You can use the Global Availability mode in one of two ways: either to load balance among wide IP pools, or to load balance within a wide IP pool. When you use the Global Availability mode to load balance among pools, the 3-DNS Controller continually sends requests to the first pool in the wide IP. When all the virtual servers in the pool become unavailable, the pool is marked unavailable and the 3-DNS Controller starts sending requests to the next pool listed in the wide IP. When the first pool is available again, the 3-DNS Controller stops sending requests to the second pool, and starts sending them to the first pool again. If you have an origin site and an overflow network, such as a CDN, you can use Global Availability to load balance between the two networks.
When you use the Global Availability mode to load balance virtual servers within a pool, the load balancing works in much the same way. The 3-DNS Controller repeatedly selects the first available virtual server in the wide IP pool to respond to requests. If that virtual server becomes unavailable, subsequent connections go to the next available virtual server listed in the pool. When the first listed virtual server becomes available again, the 3-DNS Controller distributes requests to it again.
Figure 9.1 shows the 3-DNS Controller using the Global Availability load balancing mode.
The following sections describe how to configure the Global Availability load balancing mode to load balance among pools and to load balance within a pool.
See Figure 9.2 , for an example of the syntax.
With the Global Availability load balancing mode, you can configure one data center as your primary service provider and have several alternate service providers on standby. In the wideip statement, list the virtual servers in descending order of preference. The first available virtual server is chosen for each resolution request.
Figure 9.2 shows a sample wideip definition, in the wideip.conf file, where Global Availability is the preferred load balancing mode within a pool.
// Global availability
port 80 // http
address 192.168.101.60 //New York data center
address 192.168.102.60 //Los Angeles data center
address 192.168.103.60 //Tokyo data center
The first listed virtual server (192.168.101.60 in this example) receives all resolution requests unless it becomes unavailable. If the first listed virtual server does become unavailable, then the 3-DNS Controller sends resolution requests to the second listed virtual server until the first listed virtual server becomes available again.