Nginx 502 error upstream sent too big header while reading response headers from upstream

The original setting is

Proxy_buffer_size 4k;

Proxy_buffers 4 32k;

Proxy_busy_buffers_size 64k;

In this configuration, using Fiddler for packet Analysis, it is found that as long as the size of the requested header is greater than 4378 bytes when the report 502, when the header is 4377 and below the time normal.

Change the configuration to:

Proxy_buffer_size 64k;
Proxy_buffers 32k;
Proxy_busy_buffers_size 128k;

After that, it's normal.

PS: Check the official and some of the network data, found that the buffer is used to buffer the response of the upstream (back-end) server, there is no data to find that it is also the size of the request header will have an impact. However, the problem that is currently encountered is due to the large size of the requested header. This question mark a moment.

Nginx 502 error upstream sent too big header while reading response headers from upstream