Route Traffic to different DC using GTM

Is your layout like this?

• DC1 has an LTM with a pool containing the 3 servers in DC1;
• DC2 has a different LTM with a pool containing the 3 servers in DC2;
• The GTM cluster contains the LTMs, and the LTM objects on the GTM use the bigip monitor;
• Each LTM uses a monitor to detect the application health on the servers in its pool;
• A system outside of the BIG-IPs decides when to turn up a server instance.

If so, when you say a server instance is "up" does that mean it responds to the monitor, and when it is "down", it does not?

If this is the case, then BIG-IP monitoring solves your problem. Let's say all servers in DC2 are "down". The LTM Virtual Server fronting them will also be "down" (because all of the pool members for that VS will be "down"). If a GTM pool has that LTM Virtual Server in it, the GTM would not supply the VIP on LTM in DC2 as an A record for a WIP using that GTM pool. That is, the GTM will not direct traffic the DC2 LTM VS. As soon as any servers in DC2 are declared "up" by the LTM health monitor, the GTM would start using the VS VIP for the LTM in DC2. That is, it would start directing traffic to the DC2 LTM VS (and continue directing traffic to the DC1 LTM VS, if any of the DC1 servers are still "up").

Thanks for your time, but requirement is something like this.

DC1 all 3 server will be UP (All 3 server in DC2 will be down)and at this time GTM route traffic only to LTM VS in DC1

But when 1 server in DC1 go down, 1 server will come up in DC2(this will via VMVARE or something and this server will be in the same LAN as DC1 via Extended VLAN).

Now I need the GTM to make decision to send traffic to DC1 (2 servers) and DC2 (1 server)

I apologize for being a bit obtuse. Can describe how your scenario differs from what I set out above? Is it perhaps the case that there is no LTM in DC2 and that the servers in DC2 are not part of an LTM pool? If that's true, what I say about the monitoring still holds, except that the monitor for the servers in DC2 will be defined on the GTM rather than the LTM (though, strictly speaking, if the LTM is added to the GTM cluster, either may actually perform the monitoring task).

My essential point is that, if a GTM VS (or an entire server) is marked "down" by a GTM monitor, then the GTM will not direct traffic there.