irule for multiple webservers

If you're just trying to save public IPs, you want to simply consider a "super VIP". You can use an iRule, HTTP class, or policy to define pooling based on a host name. When you add a new test application, create a new pool for it and modify the iRule/class/policy accordingly.

when HTTP_REQUEST {
    switch [string tolower [HTTP::host]] {
        "aaa.test.com" { pool aaa_pool }
        "bbb.test.com" { pool bbb_pool }
        "ccc.test.com" { pool ccc_pool } 
        default { pool error_pool }
    }
}