A major problem with TCP is that the limitations of the kernel network stack and sometimes port allocation place absurd artificial limits on the number of active connections. A modern big server should be able to have tens of millions of open TCP connections at least, but to do that well you have to do hacks like running a bunch of pointless VMs.
> A modern big server should be able to have tens of millions of open TCP connections at least, but to do that well you have to do hacks like running a bunch of pointless VMs.
Inbound connections? You don't need to do anything other than make sure your fd limit is high and maybe not be ipv4 only and have too many users behind the same cgnat.
Outbound connections is harder, but hopefully you don't need millions of connections to the same destination, or if you do, hopefully they support ipv6.
When I ran millions of connections through HAproxy (bare tcp proxy, just some peaking to determine the upstream), I had to do a bunch of work to make it scale, but not because of port limits.
