Traffic Management Persistence

UltraDNS Traffic Management services (SiteBacker, Traffic Controller, and Directional) provide dynamic DNS responses based on performance of endpoints (SiteBacker and Traffic Controller) or DNS query source IP address (Directional).  Sometimes it is necessary to maintain a user session with a specific pool group/record, this is referred to as persistence.  UltraDNS group/record persistence is largely controlled by the TTL of a previous DNS response.  

SiteBacker or Traffic Controller will return a DNS response with a configured time to live (TTL).  The user's recursive resolver will likely cache that response and the user should be directed to the same resource for as long as that response is cached (TTL). A couple implications of this approach: (1) recursive resolvers often overwrite TTL values [RFC guidance is to not exceed the TTL for caching purposes] and (2) recursive resolvers are shared resources and thus will persist other users of the recursive resolver to that resource without explicit queries to the authoritative DNS. 

Directional also returns a DNS response with a configured TTL that will control how long the response is cached at the recursive resolver.  This is similar to the source address affinity of F5 BIG-IP configurations (Note: Updates to the UltraDNS geo-location database occur weekly and it is possible that a user's source IP address could change geo-locations if it was incorrectly mapped or is more accurately mapped as a result of one of these updates.  This would result in the user losing their affinity to a particular server).