How to configure GTM for Active/Standby datacenter, I have two datacenters HO and DR, my client want me to configure GTM in a manner that all request come to HO datacenter and when HO Datacenter down it will go-to DR Datacenter using GTM
That is one of the main use cases for GTM.
You would basically configure a pool in each data center, and change the load balancing type to Global Availability. Then set a higher priority to the "HO" data center than the "DR" data center.
With that configured everything will be sent to "HO" until it becomes unavailable.
HERE is a post asking something similar to what you are asking. Read through it as there is some good info!
Hope that helps! If it does please up-vote and select this answer, it'd be greatly appreciated!