How to make nginx handle 400 error from proxy?

Question

Nginx

Gentlemen, I ask for help, Google read 5 times.
I'm setting up nginx as a front for two servers with iis.
IIS falls very cleverly (or rather, I’m still testing it), if IIS service is stopped, then connections come to port 80 and a 400 bad request error arrives in response and then the client sees: either a bad request, then the site is half loaded.

My settings are as follows: The question is how do I get nginx to handle a 400 error from the proxy and try to ask the second backend?
upstream backend {
server 192.168.194.178;
server 192.168.194.187;
}

server {
listen censored;
server_name censored;
location / {
proxy_pass backend/;
proxy_next_upstream invalid_header error timeout http_404;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header Host censored;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
access_log /var/log/nginx/billing.access_log main;
error_log /var/log/nginx/billing.error_log info;


Answer 1

Nginx wiki:
error_page
proxy_intercept_errors
400 Bad Request - The server encountered a syntax error in the client's request. I doubt that a second request will solve the problem.

Answer 2

The request is simple (just a call to the root), just like that, iis answers, the exact same request to the second server works fine. now we are fixing iis because it is bad, but still I want to know for the future

Answer 3

people, but in general, how do you solve the problem of the fact that if nginx scatters around the iis farm and one iis dies, then Windows as a whole listens to port 80, but the site is no longer there
, and then even having two servers in the farm, if one fails, we get, either service unavailable, or a site without half of the pictures and scripts,
how to configure nginix so that it will turn off the problem site