For instance, let us assume that I have a system whose entry point is Apache Knox that redirects requests to Apache NiFi. Let us further assume that I send messages A and B to the server and Apache Knox receives firstly message A and then message B. Is it possible that Apache Knox changes the order of the messages in such a way that Apache NiFi will receive firstly message B and then message A?
No, Apache Knox will not change the message order but at the same time there is no guarantee that the messages will be delivered in a specific order. Apache Knox uses the httpClient to forward requests to the backend that is being proxied after rewriting.