Today I found below error in the nginx logs.
Upstream timed out (110: Connection timed out) while reading response header from upstream
This error generally occurs when nginx is configured as reverse proxy to other webserver like Apache and till now I was fixing it by increasing the proxy_read_timeout in nginx configuration.
Nginx Reverse Proxy
Increase the proxy_read_timeout in nginx configuration file.
But this server was standalone nginx server with php-fpm. So I had to increase the fastcgi_read_timeout.
Standalone Nginx + PHP-FPM
Increase the fastcgi_read_timeout