In order for a collision to take place, we’d have to get a new connection from an existing client, AND that client would have to use the same port number that it used for the earlier connection, AND our server would have to assign the same port number to this connection as it did before.
Ephemeral ports aren't assigned to inbound connections, they're used for outbound connections. So, for the client-to-nginx connection, both the server IP and port are fixed (the port will be either 80 or 443) - only the client IP and port change, so for a collision all you need is for a client to re-use the same port on its side quickly.
For the nginx to node connection, both IPs and the server port are fixed, leaving only the ephemeral port used by nginx to vary. You don't have to worry about out-of-order packets here though, since the connection is loopback.
Note that only the side of the connection that initiates the close goes into TIME_WAIT - the other side goes into a much shorter LAST_ACK state.
So just to be sure, some noobs questions: The 'Ephemeral Ports' and the 'TIME_WAIT state' tricks are here to handle the connections from nginx to Node.js (not for the client to nginx)?
Socket from client to nginx are well identified by the client IP an the client port. On each client request, nginx create a new socket to node.js?
There can be more than one node.js intance running? That's the main goal of nginx here, or there is some additional benifices?
> Edit, ok: "nginx is used for almost everything: gzip encoding, static file serving, HTTP caching, SSL handling, load balancing and spoon feeding clients" http://blog.argteam.com/coding/hardening-node-js-for-product...
Ephemeral ports aren't assigned to inbound connections, they're used for outbound connections. So, for the client-to-nginx connection, both the server IP and port are fixed (the port will be either 80 or 443) - only the client IP and port change, so for a collision all you need is for a client to re-use the same port on its side quickly.
For the nginx to node connection, both IPs and the server port are fixed, leaving only the ephemeral port used by nginx to vary. You don't have to worry about out-of-order packets here though, since the connection is loopback.
Note that only the side of the connection that initiates the close goes into TIME_WAIT - the other side goes into a much shorter LAST_ACK state.