large_client_header_buffers
The 'large_client_header_buffers' directive configures the number and size of buffers used for reading large client request headers in NGINX.
Description
The 'large_client_header_buffers' directive is used to set the maximum number and size of buffers that are allocated for reading client request headers when they exceed the default size. This is particularly useful when dealing with clients sending unusually large headers, such as those with many cookies or long URLs. The directive takes two parameters: the first specifies the number of buffers, while the second specifies the size of each buffer.
When NGINX receives a request, it attempts to read the headers into the designated buffers. If the total header size exceeds the capacity allocated by this directive, NGINX will respond with a '400 Bad Request' error. Administrators can adjust these values based on anticipated header sizes from clients. For example, if a server expects large cookies due to heavy user-state tracking, increasing the buffer size can help avoid unnecessary errors and improve user experience.
To leverage this directive effectively, it is crucial to monitor the actual header sizes and adjust the buffer sizes accordingly. Also, remember that setting too large a buffer size without necessity may lead to increased memory usage and potential performance issues.
Config Example
http {
large_client_header_buffers 16 32k;
}Setting the buffer size excessively high can lead to memory issues, especially under high load.
If the buffers allocated are not sufficient for header sizes, clients will receive a 400 Bad Request error.
The directive applies globally in the http context or can be set in specific server blocks. Be mindful of conflicting settings.