How to configure load balancer as reverse proxy

Can I configure Rancher’s load balancer as reverse proxy using its GUI? I have service: atex-utilities-service that has endpoint on port 8000:

/permissions/ATEX_Utilities/GetAdno/ZAJW/hanboj

I would like to run it using address:

http://projektit03.test.pl/atex/permissions/ATEX_Utilities/GetAdno/ZAJW/hanboj

I tried:

But service (express.js on nodejs) returns error:
Cannot GET /atex/permissions/ATEX_Utilities/GetAdno/ZAJW/hanboj

It seems that whole path are redirected to my service (including /atex), but I would like part “/atex” was cut off.

Have I to use haproxy.cfg? In what way?

Regards,
Grzegorz

Reading article: Question about LB with a Request Path - #4 by jkopelioff I set it:

backend atex-utilities-services
reqrep ^([^\ :])\ /atex/(.) \1\ /\2

In picture:

Regards,
Grzegorz