redirect https request based on hostname

You need to terminate the SSL on the F5 in order to be able to read the host header. Based on your statement, it looks like you are terminating the SSL on the server.

Assuming that you terminate the SSL on the F5, you can use something like this:

when CLIENT_ACCEPTED {
set DEFAULT_POOL [LB::server pool]
}

when HTTP_REQUEST {
if { [HTTP::host] eq "www.abc.com" } {
pool POOL_ABC
} elseif { [HTTP::host] eq "www.xyz.com" } {
pool POOL_XYZ
} else {
pool $DEFAULT_POOL
}
}