Current scenario:
Web app files is stored in geographically separated data centers (Server A, Server B).
Database server is also geographically separated and is used as session handler (Server C).
I am planning to replace the database server and use PHP memcache as session handler.
Questions:
Can memcache scale vertically? (e.g., session handler will now be Server C, D, E)
Can the app servers (Server A and B) "round robin" to Server C, D, E? E.g., if Server C is down, session handler will failover to Server D or E?
Do you mean memcached if that's the case then Yes, http://docs.aws.amazon.com/AmazonElastiCache/latest/UserGuide/Scaling.Memcached.html