nginx as load balancer server out 404 page based on HTTP response from app server

Question

I'm using Nginx as a load balancer with app servers behind it. If the app servers return a response of 404 not found, I would like nginx to then server out a 404 page that is local on that server. I would like to do this so my app servers don't get tied up serving a static HTML file and can instead just quickly return a response and let nginx handle serving the static stuff. Does anyone know how I can accomplish this? Basically I need some kind of conditional check based on the HTTP response. Is this possible? Thanks!

Answer 1

Simply set the proxy_intercept_errors option to on and create an nginx error page for it.

error_page 404 /404.html;

proxy_intercept_errors on;

To ensure that nginx will serve the static file from it’s document root you also have to specify the following:

location /404.html {
    internal;
}

I'm assuming here that nginx is configured to talk with your app servers as proxy, because that is the usual way and your question does not mention any of this.