Remapping Nginx 502/504 error from proxy_pass into 408 error

syntax: error_page code ... [=[response]] uri;

You forgot to specify the uri parameter (your =408 argument has been interpreted as a uri).

upd:

location / {    error_page 502 504 =408 @empty;}location @empty {    return 200 '';}

http proxy nginx

location = / {  return 200;}location ~ ^[a-z/0-9@A-Z]*$ {  error_page              502 504 =408 /;  (proxy configuration goes here)}

Other values for uri did not however.

CodeHunter