Accessing GTM's in different locations.

1st off lets explain what we have very HL

 

Site A Production Data Centre - hosts external facing websites and internal facing only systems

 

Site B DR Data Centre

 

Site C User Base with excellent routing to Site A, B and D

 

Site D User base with excellent routing to Site C and ok (backup) routing to Site A and B

 

The idea is place one GTM at site C and one GTM at site D. Preference is to route all DNS traffic SITE A/B traffic via GTM at site C if up and if down route all traffic via Site D

 

How can I make this work?

 

If I have the external web traffic how can I send this to Site C GTM over Site D GTM but send to Site D GTM if Site C fails? If I have internal traffic how can I send this to site C GTM over Site D GTM but send to Site D GTM if Site C fails?

 

Externally I have looked at •Name servers as option but there is no way to set priorities on this name servers so it could send traffic to SITE C or D GTM so not ideal •Cloud based Global Traffic Management to detect when site C or D is up or down and direct to responding site with Site C as primary. Internally I have looked at •Only option I can see is if Site C and D GTM’s are clustered and use a stretched VLAN with internal floating IP to be accessed internally for DNS queries from delegated DNS zone for SITE A /B systems

 

Would appreciate if anyone who has more experience with GTM designs could offer better way/options to deploy this solution.