reverse proxy mulitple ipython notebook servers - nginx

Question

Currently we are running an Ipython notebook server behind a nginx proxy. This works well as it is a straightforward 1-to-1 mapping.
Now we want to run multipe notebook servers behind 1 proxy. Since these servers will be dynamically added, the proxying should be dynamic as well.
Ideally I'd like to proxy on a url subpath:
http://open.net/py1 -> http://secure1:8888
http://open.net/py2 -> http://secure2:8888
http://open.net/py3 -> http://secure3:8888
etc.
Problem with this approach is that Ipython doesn't use relative url's inside it's html. extract:
<script src="/static/.../promise.min.js"</script>
<script src="/static/.../require.js"</script>
<script> ...
So inside http://open.net/py2 require.js will be loaded via http://open.net/static/.../require.js which of course will result in a 502. It should be http://open.net/py2/static/.../require.js
Question: what's a good strategy to solve this?
Constraints:
I cannot touch the source html
I cannot use subdomains for each Ipython server (as they are dynamically added)

Answer 1

what's a good strategy to solve this?
Subdomains
I cannot use subdomains for each Ipython server (as they are dynamically added)
Not true.
# this will only py<some-digits> subdomain.
server {
listen 80;
server_name ~^(?<sub>py\d+)\.example\.com$;
# now you have $sub variable that contains subdomain
# and could be used to choose what server you want to connect
...
}
# catch all server block that simple shows 404 for any request
server {
listen 80 default_server;
return 404;
}