The Role of DNS

The array software relies on the DNS to provide load balancing, as described in "Load Balancing".

When all hosts and services are up and under a normal load, the array's DNS works as a conventional DNS round robin. It is when there is a host or service failure, or if a host becomes overloaded, that the array software intervenes to balance the load across the array. The software accomplishes this by removing the service address of the failed or overloaded host from the array's DNS zone. As a result of this intervention, no new client requests will be connected to a service address associated with a failed or overloaded object.

The threshold at which a host becomes overloaded, as well as the threshold at which a formerly-overloaded host is considered available again, are configurable parameters.

As part of its manipulation of the array's DNS zone, in a situation where one or more hosts in the array is moving back and forth between overload and normal load, the array software always keeps the least-loaded hosts in the zone.

In support of the array software's modification of the DNS round robin, you designate one host within the array as the DNS server for the domain formed by the array. (The choice of which host is arbitrary.) The DNS itself operates under control of the array software, so that if the DNS software or the host on which DNS is running fails, the service address of the DNS moves to a different machine in the array. Array software is designed so that one host runs the DNS and the remaining hosts in the array act as hot spares for the DNS host.

In addition to the array software's use of DNS for load balancing, the software also relies on the DNS outside of the array to resolve the name of the subdomain formed by the Netra Proxy Cache Array. This subdomain consists of the DNS zone formed by the service addresses in the array. This means you must configure your existing DNS to point to the array's DNS to resolve the name of the array's proxy cache service. An example of such a configuration is shown in Chapter 3 of the Netra Proxy Cache Array Configuration Guide.