Does NGINX allow for switching load to another server without losing the requests?

Does NGINX allow switching load from one server to another without losing the request?

I have a SOAP API, NGINX forwards the request to one of three servers each which forwards it to a queue and then waits for a response from the queue and then the client waits for a response from the API. If the client doesn't get the response, the request still goes through, only the client doesn't know that that the action he executed finished successfully.

So in the event that I need to upgrade one of these SOAP frontends, I need to switch load to one of the other two frontends, but without dropping any of the existing connections, is this possible with NGINX?