GSLB Overview
GSLB is based on DNS and uses a very similar mechanism as described above.
The ADC can change the response based on several factors described later in the guide. The ADC makes use of the monitors checking for availability of remote resources by accessing the resource itself. However, to apply any logic, the system must first receive the DNS request.
Several designs allow this. The first is where the GSLB acts as the authoritative nameserver.
The second design is the most common implementation and is similar to the authoritative nameserver configuration but uses a sub-domain. The primary authoritative DNS server is not replaced by GSLB but delegates a sub-domain for resolution. Either directly delegating names or using CNAMEs allows you to control what is and is not handled by the GSLB. In this case, you don’t have to route all the DNS traffic to the GSLB for systems that don’t require GSLB.
Redundancy is provided so that if one nameserver (GSLB) fails, then the remote nameserver automatically issues another request to another GSLB, preventing the website from going down.