A server is a regular server in the cloud. There are millions. You can write a server with your keypair, im sure you know. Just as you can write to relays. You can write events to multiple servers, and you can write events to multiple relays. There are not "infinite" relays, there are 100s. But there are millions of servers. So servers are actually more resilient than relays. It's the fact that events can live anywhere that allows replication and resilients, not properties or relays, http, websockets or domains.