update comment on Serve()

server.go

@@ -813,6 +813,18 @@ func (l *listenSocket) Close() error {
 // Serve returns when lis.Accept fails with fatal errors.  lis will be closed when
 // this method returns.
 // Serve will return a non-nil error unless Stop or GracefulStop is called.
+//
+// Note: All supported releases of Go (as of December 2023) override the OS
+// defaults for TCP keepalive time and interval to 15s. To enable TCP keepalive
+// with OS defaults for keepalive time and interval, callers need to do the
+// following two things:
+//   - pass a net.Listener created by calling the Listen method on a
+//     net.ListenConfig with the `KeepAlive` field set to a negative value. This
+//     will result in the Go standard library not overriding OS defaults for TCP
+//     keepalive interval and time. But this will also result in the Go standard
+//     library not enabling TCP keepalives by default.
+//   - override the Accept method on the passed in net.Listener and set the
+//     SO_KEEPALIVE socket option to enable TCP keepalives, with OS defaults.
 func (s *Server) Serve(lis net.Listener) error {
 	s.mu.Lock()
 	s.printf("serving")