@stebo keep in mind the rewrite feature works when a client make a request to the ingress controller. If your application returns a redirect (just as an example) to /API/contracts/..... then you will get a 404 from the ingress controller. There is no rewrite of the content returned from your application.
You can do that using something like:
nginx.ingress.kubernetes.io/configuration-snippet: |
sub_filter '/API/contracts/' '/20190220/API/contracts/';
Keep in mind that will work but impacts the performance. This can be avoided if you can return relative links.