Dedicated IPs are designated for a single site only. Some options (like SSL) require a dedicated IP. Shared IPs can host many sites.
Yes, one public IP is fine. The cluster nodes on the internal network must reside on the same network segment.
If the reseller need to set up SSL for a secure site, a dedicated IP is needed. Also many resellers want their own IPs for custom ns1 and ns2.mycompany.com name servers and to set up their own reverse dns.
IP Management FAQ
What is the difference between "dedicated" and "shared" IPs?
Dedicated IPs are designated for a single site only. Some options (like SSL) require a dedicated IP. Shared IPs can host many sites.
If we only had one public IP, could we setup a cluster service? Would the service run on private IPs? The setup would be with one public IP and behind it, imagine five servers doing load balancing and clustering. Would this be possible?
Yes, one public IP is fine. The cluster nodes on the internal network must reside on the same network segment.
Why would a reseller want a dedicated IP? Wouldn't it be enough to use the IPs of the system?
If the reseller need to set up SSL for a secure site, a dedicated IP is needed. Also many resellers want their own IPs for custom ns1 and ns2.mycompany.com name servers and to set up their own reverse dns.