Using kdb as an nginx backend isn't going to work well at high loads because you'll run out of TCP port numbers to use for connections. You might try keepalive,

Using kdb as an nginx backend isn't going to work well at high loads because you'll run out of TCP port numbers to use for connections. You might try keepalive, but it still requires clients to behave. It's in lua because nginx doesn't have a module system: getting a lua module available on all our edge nodes caused less friction than a bunch of nginx patches and an nginx deploy.