In the attached picture, I have drawn some servers on which the application code is running. Pls correct me if I have done it incorrectly.

Q - when we follow the Master Slave architecture "at application level", Pls consider the following two cases:
CASE 1 -
does the same [only one] application code instance runs on all the servers Across All the Availability Zones and Across All the Data Centers?
OR
CASE 2 -
Each server runs an application code instance of its own, independently(ISOLATED)?

If the answer is case 2 then how is the concurrency handled?

Bcs the other thread running in other server can't find if the monitor was locked by some thread in the current server instance.