The following is an example iRule where you can redirect the same websites across different regions based on the clients IP address.
$::regionXclients is a datagroup that contains network addresses of clients in the region1 which can be any region you wish to base your logic on. $::pool_regionXservers corresponds with the resource of there the pool of servers
For example: region1clients contain clients in the east coast, region2clients contain clients in the west coast, region3clients contain clients in the Europe and finally region4clients contain clients for asia pacific. pool_region2servers contain servers for region1clients, pool_region2server contain servers for region2clients, etc. However, if say pool_region1servers is down then it will send region1clients over to server to pool_region2servers and so forth.