it doesn't work once I applied the irules to the virtual server

Is this because of the iRules? Here is my intention : I have two different domain: aaa.com and bbb.com Both of these domains has resolved their IP address, which is c.c.c.c: AA as inbound IP address at the virtual serverA at LTM. Now, I have created two pools, one is for aaa.com and the name of the pool is: pool_a, and its member is A.A.A.A: BB, which is the IP address of a Web server. the other one is for bbb.com, and the name of the pool is: pool_b, and its member is C.C.C.C:DD, which is IP address of the XMPP server.

Now I want to create a BigIP load balance with the domain aaa.com and bbb.com at the same virtual server, which means I need an iRules: and this is the iRules that I created:

when HTTP_REQUEST { switch [HTTP::host]] { "aaa.com" { pool pool_a } default { pool pool_b } } } But once I applied this iRules to the virtual server, and I verify the results and it didn't work.