Proxy Error[502] on web page with apache

Hello everyone

I'm trying to install GitLab on my server, and I have this error when trying to reach the web page of gitlab :

Proxy Error

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

Reason: Error reading from remote server

But, all the componants of gitlab are running normally, and the return of

sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production

showed no errors. (Unicorn is working)

So I think the problem come from Apache, but after tons of attemps, I could not figured out where the problem is.. So there is my apache conf for gitlab :

`<VirtualHost *:80>

ServerName gitlab.domain.com
ServerSignature Off
ProxyPreserveHost On
ProxyPass / http://www.domain.fr:8080/ retry=1 acquire=3000 timeout=600 Keepalive=On
AllowEncodedSlashes NoDecode
<Location />
     Order deny,allow
     Allow from all
     Options -Indexes -ExecCGI
     ProxyPassReverse http://127.0.0.1:8080
     ProxyPassReverse http://gitlab.domain.com/
</Location>
RewriteEngine on
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule .* http://127.0.0.1:8080%{REQUEST_URI} [P,QSA]
DocumentRoot /home/git/gitlab/public
ErrorDocument 404 /404.html
ErrorDocument 422 /422.html
ErrorDocument 500 /500.html
ErrorDocument 503 /deploy.html
LogFormat "%{X-Forwarded-For}i %l %u %t \"%r\" %>s %b" common_forwarded
ErrorLog /var/log/gitlab/gitlab.domain.com_error.log
CustomLog /var/log/gitlab/gitlab.domain.com_forwarded.log common_forwarded
CustomLog /var/log/gitlab/gitlab.domain.com_access.log combined env=!dontlog
CustomLog /var/log/gitlab/gitlab.domain.com combined 

`

So there is my question, where may be the problem? And what kind of mistakes can create a proxy error?

There is some other informations : Nginx is disabled, SSL is disabled, The timeOut on unicorn.rb is set as 60.

Thank you all for your time and if you have any question, feel free to ask