A connection is identified by the tuple {host IP, host port, client IP, client port}. The server listens on one port, but the client has a separate port for each connection. This means that there can be 65k connections for a single {host IP, client IP} combination.
There's two ways to get more connections: use more client IPs or use more host IPs. In this post the OP has decided to add more host IPs.
That would depend on if it matters to the WebSocket server if connections are from one or multiple IPs. In this case I would not think that there's any difference as far as the WS library is concerned. Maybe it has some effect on the OS kernel's networking routines, but I would not expect it to be big.
> The client side has similar settings but does not need to set up multiple IP addresses, obviously
Also as I know, Linux will only use one IP for outbound connections, unless forcefully bind to another IP address in the code.
The server only uses only one port. 9001 according to the code. https://github.com/uNetworking/uWebSockets.js/blob/875f16e1f...
This blog post does not make any sense.