Nginx reverse proxy running on other server than Owncloud installation

Hello

I'm having a few problems setting up my reverse proxy to my owncloud. This is my nginx config file for owncloud: http://pastebin.com/1EpUpjtH
I'm failing where to direct it to the URL where owncloud is installed on my network: 192.168.178.200:8000.

Server configuration
Operating system: Docker setup
Web server: Docker provided by owncloud
Database: Docker provided by owncloud
PHP version: Docker provided by owncloud
ownCloud version (see ownCloud admin page): 9.0.2
Updated from an older ownCloud or fresh install:Docker provided by owncloud
ownCloud log (data/owncloud.log):

If any information is missing give me a shout
Thanks for your help