Using gitlab with apache2

Question

I'm trying to install GitLab on my Debian 8 server while using apache2 instead of nginx.

Problem is that I get

Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET /.

Reason: Error reading from remote server

Apache/2.4.10 (Debian) Server at gitlab.o190.orange.fastwebserver.de Port 80

when trying to access the webpage.

My virtual host configuration

<VirtualHost *:80>
  ServerName gitlab.o190.orange.fastwebserver.de

  # Custom log file locations
  ErrorLog  /var/log/apache2/gitlab_error.log
  CustomLog /var/log/apache2/gitlab_access.log combined

  ProxyRequests     Off
  ProxyPreserveHost On
  ProxyPass / http://127.0.0.1:8080/
  <Location />
    ProxyPassReverse /
    Order deny,allow
    Allow from all
  </Location>

</VirtualHost>

gitlab_error.log

[Fri Sep 11 05:23:21.619418 2015] [proxy_http:error] [pid 5949] (20014)Internal error: [client 37.120.47.14:49199] AH01102: error reading status line from remote server 127.0.0.1:8080
[Fri Sep 11 05:23:21.619467 2015] [proxy:error] [pid 5949] [client 37.120.47.14:49199] AH00898: Error reading from remote server returned by /