it is possible to use floating ip to communication to internet

Roman_ What I understand is that you have a server that is the source of communication and you want it to be able to reach out to the internet using the floating IP in an HA pair of F5 BIG-IP LTM? You can configure a forwarding virtual server and then apply an iRule to it that specifies specific sources and any destination outside of your network and then for it to SNAT from a snat pool, in that snat pool you configure the floating IP, and finally in the iRule you created you put in this snat pool IP for SNAT under the specific traffic that you defined. I believe something similar to the following would work for you when applied to your forwarding virtual server.

when CLIENT_ACCEPTED priority 500 {

    if { [class match [IP::addr [IP::client_addr] == CLASS-Source-IPs]] } {
        if { [class match [IP::addr [IP::remote_addr] contains CLASS-Internal-IPs]] } {
            forward
        } else {
            snatpool SNAT_FloatingIP
        }
    }

}

The CLASS labeled as CLASS-Source-IP should have the specific sources in question, the one labeled CLASS-Internal-IPs will have internal destinations that you would be reaching out to that you wouldn't want to SNAT the traffic, and finally the SNAT pool list labeled SNAT_FloatingIP would have the floating IP configured in it.