Proxy with IIS a cherrypy app that has route-dispatching

The question is how to get IIS to proxy a webapp with both static data and webservices.

I made a cherrypy app to search in a large number of images for specific tags. With cherrypy, the dynamic functionality is served with dispatching, as sketched below for the find service:

config = { '/' : { 'tools.staticdir.on' : True, 
                   'tools.staticdir.root' : <root>,
                   'tools.staticdir.dir' : <dir> },
         { '/find' : { 'request.dispatch' : cherrypy.dispatch.MethodDispatcher(), 
                       'tools.response_headers.on' : True,
                       'tools.response_headers.headers' : [('Content-Type', 'text/plain') ]}}

This works using cherrypy as server, say on //127.0.0.1:1414

I was able to serve my cherrypy app to /myapp with Apache2 if I proxy every service of my app.

<VirtualHost *:80>
  # static stuff
  ProxyPass /myapp  http://127.0.0.1:1414
  ProxyPassReverse /myapp http://127.0.0.1:1414

  # service stuff
  ProxyPass /find  http://127.0.0.1:1414/find
  ProxyPassReverse /find http://127.0.0.1:1414/find
</VirtualHost>

So far so good, but on the windows server that should host this, there is an IIS app-server. This has the usual windows interface with many buttons and cascading 'more or less advanced settings'.

I followed https://docs.microsoft.com/en-us/iis/extensions/configuring-application-request-routing-arr/creating-a-forward-proxy-using-application-request-routing

• enabled proxy on the 'application request routing page'
• created a reverse proxy rule (urlrewrite)

The rule as created maps myhost/myapp with pattern (.*) with rewrite to //127.0.0.1:1414/{R:1}. There is a web.conf that says:

<rules>
   <rule name="ReverseProxyInboundRule1" stopProcessing="true">
      <match url="(.*)" />
      <action type="Rewrite" url="http://127.0.0.1:1414/{R:1}" />
   </rule>

This works for the static part. It does not work for the services; I get a 500 for that. Whatever I change on the pattern seems to make no difference: static is ok, services not. Any hint ?