Auth cookie shared between web sites

Question

I have two web sites in two different regions running the same app with a DNS Failover that switch to region 2 if region 1 is down. 
Is it possible to keep users logged in when they logged in in region 1 and then are redirected to region 2? 

Answer 1

https://msdn.microsoft.com/en-us/library/eb0zx8fc.aspx
To configure forms authentication across applications, you set attributes of the
forms and
machineKey sections of the Web.config file to the same values for all applications that are participating in shared forms authentication.
The following example shows the
Authentication section of a Web.config file. Unless otherwise noted, the
name, protection, path,
validationKey, validation,
decryptionKey, and decryption attributes must be identical across all applications. Similarly, the encryption and validation key values and the encryption scheme and validation scheme used for authentication tickets
(cookie data) must be the same. If the settings do not match, authentication tickets cannot be shared. For information about how to generate values for the
validationKey and decryptionKey attributes, see
How To: Configure MachineKey in ASP.NET 2.0. (This topic applies to ASP.NET version 2.0 and to later versions.)
Frank