Hi,

first of all with one database server you will have a SPOF and you will deflect your SPOF from keystone to MySQL/Postgres whatever. I would prefere a master - master setup with failover IP for MySQL.

"Will there be data corruption because two keystone writing to same db?" => No :) Each modern database will have a locking management so you can run hunderds of thousends keystone server if you have a fast database server/cluster :)

Here is one possible solution of HA but not my preferred. Thats a cold standby keystone but i think with a loadbalancer in front keystone servers will have more flexability and your requests will balanced to all servers.

Cheers Heiko