How to redirect user to URL based on entered CNAME

Just a thought, but the first issue is generally resolved with a CNAME. I don't believe GTM can natively issue a CNAME from a given short name, so an iRule like this (applied to the LTM listener VIP) could work. This is a very simple example, so I'm sure there's a better way.

when DNS_REQUEST {
    switch [string tolower [DNS::question name]] {
        "service-a" {
            DNS::answer insert "service-a CNAME service-a.company.com"
            DNS::return
        }
        "service-b" {
            DNS::answer insert "service-b CNAME service-b.company.com"
            DNS::return
        }
    }
}

Where "service-a.company.com" and "service-b.company.com" resolve to the same virtual server IP. Then use an iRule on the VIP that validates the Host header:

when HTTP_REQUEST {
    if { [string tolower [HTTP::host]] equals "service-b.company.com" } {
        HTTP::redirect "http://service-a.company.com/service-b"
    }
}