9800L WLC redundancy

[vban]

I require assistance with setting up the 9800L WLC as both primary and redundant devices.

We currently have approximately 50 APs and 2,504 WLCs. Therefore, we would like to replace the old WLC with the new 2 9800L Wireless LAN Controller (WLC). Two of our 9800L WLCs are not yet configured. For this reason, we want to set up one WLC as the primary at the major site and another as the secondary at a different location.

Therefore, I'm asking how I should go about connecting these two new 9800Ls at two distinct places to the switch and designating one as primary and redundant.

[Saikat Nandy]

If the 2 locations are interconnected via any means, like dark fibre, you can think about HA-SSO (RP connectivity through switches with non-routable L2 VLAN) or else the available option for you is going to be N+1 - means one WLC will hold all the APs (call it Primary) and the other one will be having an exact replica config (with a different WMI IP address, call it Secondary) but will be sitting idle. In case if your Primary WLC goes down, the Secondary will take over the load and all the APs will join there. Note, in HA-SSO seamless failover happens for AP/Client but in N+1 it's not a seamless failover. Refer - 
N+1 - https://www.cisco.com/c/dam/en/us/td/docs/wireless/controller/9800/17-4/deployment-guide/c9800-n-plus-1-high-availability-wp.pdf
HA-SSO - https://www.cisco.com/c/dam/en/us/td/docs/wireless/controller/9800/17-6/deployment-guide/c9800-ha-sso-deployment-guide-rel-17-6.pdf

[Rich R]

>  50 APs and 2,504 WLCs
I suspect you mean 2,504 users?

Anyway see the links @Saikat Nandy provided but I think you are probably best to look at N+1 redundancy.
But you don't need to have all the APs on one WLC.  You can split them between the two WLCs.  I would highly recommend that in fact.  Configure the sites with their closest WLC as primary and the other as secondary.  You configure that as the AP HA Primary/Secondary on the AP settings.  Then configure mobility between the 2 controllers.