I just ran into an issue where a request made to localhost:8080 from curl was hitting a different server than the same request made from inside Node. lsof -i :8080 revealed that two processes were both binding onto the same port:

COMMAND   PID  USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node    51961 mball   14u  IPv4 0xd980e0df7f175e13      0t0  TCP *:http-alt (LISTEN)
java    62704 mball  320u  IPv6 0xd980e0df7fe08643      0t0  TCP *:http-alt (LISTEN)

How is this possible? Were they binding onto different interfaces? Or was it the IPv4 vs 6?

If you're curious, node was hitting the other node process, curl was hitting the java process. The java process was started after the node process.