I've been working on my setup for some time now, but finally I think the problem I ran into is solved.

I have debian server which is providing web services for my team. Everything we need is running in separate docker container.

In this environment we wanted to run XO as well. So I used one of available images to start work.
(https://hub.docker.com/r/ezka77/xen-orchestra-ce) and everything worked fine.

Xen Orchestra builded, started and I could connect to it using our nginx proxy docker as long as it had location http://myip/ . When I wanted to move page to http://myip/xen I started to have troubles. Sigin page didn't want to load. It was redirected to http://myip/sigin not http://myip/xen/signin and nginx didn't redirected it to correct docker.

I used niginx configuration from docs - https://xen-orchestra.com/docs/reverse_proxy.html

After some investigation I found solution to this problem, but I'm not familiar enough with nginx to be sure that this is the best way to resolve my problem.

I changed one line in given config:
proxy_redirect default;
to
proxy_redirect / /xen/;
and now everything is working fine. When I connect to http://myip/xen browser is redirected to proper page http://myip/xen/sigin.

I can't be sure that this isn't problem with my nginx docker as I'm pretty new in this topic. I think that it is worth being at least checked by more expirenced users both nginx and xen orchestra. Maybe example configuration in documentation should be updated if my problem is real not only for me.