In the following
example topology, clients want to reach servers that are hosting
web applications in the cloud. An external Elastic Load Balancer
(ELB) connects to firewalls, which connect to internal ELBs that
connect to the servers. Over time, Amazon Web Services (AWS), for
example, adds (and removes) IP addresses for the FQDN assigned to
the internal ELBs based on the demand for services. The flexibility
of using an FQDN for NAT to the internal ELB helps the policy to
resolve to different IP addresses at different times, making destination
NAT easier to use because the updates are dynamic.