Kong Gateway logs show the following error:
upstream sent too big header while reading response header from upstream"upstream sent too big header while reading response header from upstream" error when response headers exceed the Nginx proxy buffer size in Kong Gateway
Uses:
Kong Gateway
TL;DR
Why does Kong Gateway log “upstream sent too big header while reading response header from upstream”?
This error means the upstream’s response headers are larger than Kong’s Nginx proxy buffer size, so the response is rejected and the request fails. Increase the buffer size by setting both KONG_NGINX_PROXY_PROXY_BUFFER_SIZE and KONG_NGINX_PROXY_PROXY_BUFFERS (both must be set together) to values larger than what your environment needs, for example 16k and 4 16k instead of the defaults 4k and 8 4k.
Problem
Cause
These logs will be written when the headers sent by the upstream are too large for the Nginx proxy buffer size set in the Nginx layer in Kong Gateway. The response is effectively rejected and requests may error out / fail in this situation.
Solution
To solve this problem, the following environment variables can be added to the Kong deployment configuration to increase the buffer size for the environment: KONG_NGINX_PROXY_PROXY_BUFFER_SIZE and KONG_NGINX_PROXY_PROXY_BUFFERS. Both must be set together - setting only proxy_buffer_size without also setting proxy_buffers will cause Kong to fail to start entirely. The values of these properties should be set a bit larger than what is needed in the environment. For example, setting proxy_buffer_size to 16k and proxy_buffers to 4 16k may be useful, compared to the defaults of 4k and 8 4k respectively. For details on what the proxy_buffer_size and proxy_buffers Nginx directives do specifically, they are outlined in the official Nginx HTTP Proxy module documentation. For instructions on injecting Nginx directives to the Kong Gateway nodes, please review the Kong Gateway Nginx Directives documentation.