[kiitos]

> Both load balancers and backend servers can juggle millions of concurrent connections nowadays.

Maybe with SO_REUSEPORT, but not in general.

A TCP connection is identified by a 5-tuple that requires a unique port for both the client and server. TCP represents ports as uint16s, which means the max number of possible ports per address is 65536.

tl;dr: 1 server IP address = no more than 64k incoming connections

[otterley]

Yes, I'm aware that 4-tuples must be unique. And so, by having a LB and/or server bind to more than one IP address, you can easily overcome that limit.

[kiitos]

If you have multiple client-accessible IP addresses available to a server, I guess? But that's in no way common?

[otterley]

It's quite common in Kubernetes deployments, where each server in a separate Pod binds to a separate IP address.

And, as I said before, with DSR, there's a broad diversity of client IPs, so a single server address doesn't typically cause concerns with 4-tuple exhaustion.

[kiitos]

I think we're speaking from wildly different, and incompatible, contexts.

DSR is niche at best, not something that can be assumed.