Plesk: upstream sent to big headers

This help center article will show you why this error message appears and how you can easily fix it.

Cause

The error occurs when a request cannot be processed by the proxy server because the buffer size is insufficient.

Troubleshooting for individual domains

To fix the error yourself, navigate to your Plesk Control Panel.

The following help center article shows you how to log in to your Plesk Control Panel: Logging into the Plesk Control Panel

Nginx with Proxy mode deactivated

If you are using NGINX as PHP handler with proxy mode disabled, navigate to example.com (your domain) → Hosting & DNS → Apache & nginx.

There you can define the following instruction under additional Nginx instructions:

fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;

Nginx with proxy mode enabled

If you are using Nginx with enabled proxy mode, you can use the following instruction:

proxy_buffers 8 16k;
proxy_buffer_size 32k;

Troubleshooting for all domains

To fix the error for all domains, log in to your server as root user via SSH.

Open the Nginx configuration with the following command:

nano /etc/nginx/nginx.conf

Customize the configuration in the http { block to the following:

proxy_buffers 8 16k;
proxy_buffer_size 32k;
fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;

After a successful config test with nginx -t, reload the Nginx service by executing the following command:

systemctl reload nginx