I installed nagios and apache using https://www.digitalocean.com/community/tutorials/how-to-install-nagios-4-and-monitor-your-servers-on-ubuntu-14-04
OS: Ubuntu
But after that, gitlab(using nginx) that is already installed in my server stopped working. But another website that is using the same nginx is working.
Stopped means, nginx and gitlab processes are running(I guess) but site is not opening, saying "502 Bad Gateway".
Note that I stopped services nagios and apache2 but still.