Nginx local fallback error page if proxy destination is unavailable

Question

I'm forwarding requests to a local service through a Nginx server. What I try now to accomplish is to fallback to a local error page in case the service becomes unavailable.

My current configuration is

server {
    listen       80;
    server_name  "";

    location / {
        proxy_pass  http://127.0.0.1:9080;
        proxy_set_header    Host $host;
        proxy_set_header    X-Real-IP   $remote_addr;
        proxy_set_header    X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_connect_timeout 1;
        proxy_next_upstream error timeout http_500 http_502 http_503 http_504 http_404;
        proxy_intercept_errors on;
    }

    error_page 501 502 503 @maintenance;
    location @maintenance {
            root   /locust/www/fallback/htdocs;
            index  index.html index.htm;
    }
}

Proxying works, but as soon as I make my service on 9080 unavailable the index.html of my maintenance location is NOT displayed.

Any suggestions on what is wrong with this config?

Answer 1

Actually, I only had to slightly modify your config:

error_page 501 502 503 /500.html;
location = /500.html {
        root   /locust/www/fallback/htdocs;
}

and obviously rename the index.html you want to present to 500.html.

Answer 2

Try to specify exact url for the error page like:

    proxy_intercept_errors on;
    error_page  500 502 503 504 402 403 401  /500.html;
    root   /locust/www/fallback/htdocs;