How to Resolve \"Upstream Sent Too Big Header\" Errors in Nginx?

Troubleshooting "upstream sent too big header" Errors

Encountering "upstream sent too big header" errors in Nginx can be frustrating, especially when followed by "http request count is zero while sending response to client" messages. These issues typically arise when the headers returned by the upstream server exceed the maximum size allowed by Nginx.

Cause and Solution

The "fastcgi_buffers" and "fastcgi_buffer_size" directives play a crucial role in managing header sizes. These directives define the number of buffers used for storing incoming headers and the size of each buffer, respectively. Insufficient buffer size can lead to the "upstream sent too big header" error.

To resolve this issue, increase the values of both "fastcgi_buffers" and "fastcgi_buffer_size" in your Nginx configuration file. The following lines will configure Nginx to use 16 buffers, each with a size of 16 kilobytes:

fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;

Additional Considerations

Apart from adjusting the buffer settings, consider reviewing the headers sent by the upstream server. Long or complex headers can also contribute to the problem. Additionally, ensure that your proxy settings are correctly configured, as any misconfigurations can introduce similar errors.

Conclusion

By increasing the buffer sizes for headers, you can address the "upstream sent too big header" errors and improve the overall performance of your Nginx server. Remember to review the configuration and headers to optimize further and avoid future issues.

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