iRule for redirect to proxy server.

Do you wish to forward a request from the BIG-IP to a pool of proxy servers, or do you intend for the BIG-IP to cache the content (which a squid caching server would do in this case)? Further, are you intending to accept HTTPS requests and, on the backend, also use TLS/HTTPS? Do you want to forward for just requests against a specific domain (domain.domain.eu in your example)?

If you don't care about the domain and you are not caching the content on the BIG-IP, then you can use a straight fastL4 Virtual Server:

• https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm-concepts-11-5-1/11.htmlunique_1890659034

If you want to handle requests only for specific domains, you have two choices:

1. Use the CN on the certificate (and possibly the alts);
2. Unencrypt on the BIG-IP and use the Host header (as you appear to be doing above).

Assuming you require 2, you must create a Virtual Server with a client-ssl profile:

• SOL14783: Overview of the Client SSL profile (11.x - 12.x)

If you subsequently must re-encrypt the request toward the parent cache, you must also use a server-ssl profile:

• SOL14806: Overview of the Server SSL profile (11.x - 12.x)

From there, to forward only traffic for the specified domain, you may use an iRule:

when HTTP_REQUEST {
    if { [getfield [string tolower [HTTP::host]] : 1] eq "domain.domain.eu" } {
        pool parent-proxy-pool
    }
}

or with a Local Traffic Policy:

ltm policy parent-proxy {
    controls { forwarding }
    requires { http }
    rules {
        rule-domain.domain.eu {
            actions {
                0 {
                    forward
                    select
                    pool pool-parent-proxy
                }
            }
            conditions {
                0 {
                    http-host
                    values { domain.domain.eu }
                }
            }
            ordinal 1
        }
    }
    strategy first-match
}

If you require local caching on the BIG-IP, that is a matter of provisioning Application Acceleration Manager (AAM) and assigning a to the listening Virtual Server.

If I've completely misunderstood your question, I apologize in advance and look forward to hearing more :).