When you try to load Drupal Web app on Nginx and Nginx Web server through an error: Upstream sent too big header while reading response header from upstream, client: IP-Address, server: ServerName, Request   Problem:   The problem is that Nginx is not configured to wait for FastCGI a PHP processor to respond, chances are that Nginx has a time-out limit defined in its config file.    Solution:   Just add these lines of code inside the http block in nginx.conf file : client_max_body_size 500M; fastcgi_buffer 8 16k; fastcgi_buffer_size 32k;  - Nginx times-out because of the data being processed by the php-fpm server is too big. One way to solve this is by adjusting the php.ini file by increasing max-execution-time from 30 to 60 (this time is in seconds). - After making a change to php.ini restart the php-fpm by using this command: systemctl restart php7.2-fpm (this depends on what version of php fpm you are using)   - Likewise, you would want to make changes to the http block in Nginx config file like so:       http { fastcgi_buffer 8 16k; fastcgi_buffer_size 32k; fastcgi_connect_timeout 300; fastcgi_send_timeout 300; fastcgi_read_timeout 300;               } - Reload Nginx and PHP7.2-fpm   - If the above does not work, edit (etc/php-fpm.d/www.conf) and change request_terminate_timeout = 300, after this reload php and Inginx [NB] If you find yourself dealing with this problem, then the issue is bigger than just increasing time-outs but work on optimizing the performance of your application by decreasing the database queries or increasing the application start up time.