I'm trying to understand how IP addresses work. For instance, when you rent space at a colo for your server, and say, "I need 20 IP addresses", how are they giving those to you, and is your server aware of them or are they just paths to your server from the outside? Does the colo have a bunch of IP addresses, and they're simply routing traffic on the 20 that you purchased to your server, or does something else happen? Then, when it comes to your web server (Nginx, in my case), can you control which IP addresses to listen on or would all traffic to domains whose A Record points to any of your server's IP addresses be routed to the same place (same place in Nginx that is)?
A single physical server can have many IP addresses, right?
Finally, if I have 2 servers (one for fail-over) in the same colo, one right on top the other, is it possible to have traffic that's always coming in on the same IP address route to the backup server when the other server goes down?