How to Fix \'upstream sent too big header\' Errors in Nginx?

Fixing "upstream sent too big header" Errors During Response Processing

The error message "upstream sent too big header while reading response header from upstream" indicates that the server is receiving a header from the upstream server that exceeds its configured size. This can occur when there is an excessive amount of data in the header response.

Identifying the Root Cause

In the provided error example, the issue seems to be caused by an unusually large URL with multiple repetitions separated by commas. This excessive length can exceed the allowed header size in Nginx, resulting in the error.

Configuration Adjustments

To resolve this issue, you need to adjust the buffer size and buffer count configurations within your Nginx conf file:

<code class="nginx">fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;</code>

Explanation:

• fastcgi_buffers: Specifies the number of buffers used for fastcgi response processing. Increasing this value allows Nginx to handle larger headers.
• fastcgi_buffer_size: Determines the size of each individual buffer. A larger buffer size can accommodate more data in a single buffer.

Additional Considerations

• Review Upstream Server: Check if the upstream server is sending excessive headers and consider optimizing it to reduce header size.
• Disable Compression: Disable any compression on the upstream server, as this can increase the header size.
• Check Response Headers: Inspect the response headers from the upstream server using developer tools to identify any unusually large headers.

Conclusion

By adjusting the buffer size and buffer count configurations as suggested, you can resolve the "upstream sent too big header" error and ensure smooth response processing in Nginx.

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