Connections are also rate limited in order to prevent abuse of the API. If you are receiving a
503: Server Error you may have too many open connections.
The limit of open connections at any given time is not fixed, but generally it is ~20 concurrent open connections per IP address. Since this limit can vary from day to day depending on our traffic, we recommend opening a maximum of 10-15 connections per IP address.
The 0x API uses persistent connections via http keep-alive.