nginx not serving my error_page

Question

I have a Sinatra application hosted with Unicorn, and nginx in front of it. When the Sinatra application errors out (returns 500), I'd like to serve a static page, rather than the default "Internal Server Error". I have the following nginx configuration:

server {
  listen 80 default;
  server_name *.example.com;
  root /home/deploy/www-frontend/current/public;

  location / {
    proxy_pass_header Server;
    proxy_set_header Host $http_host;
    proxy_redirect off;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Scheme $scheme;
    proxy_connect_timeout 5;
    proxy_read_timeout 240;
    proxy_pass http://127.0.0.1:4701/;
  }

  error_page 500 502 503 504 /50x.html;
}

The error_page directive is there, and I have sudo'd as www-data (Ubuntu) and verified I can cat the file, thus it's not a permission problem. With the above config file, and service nginx reload, the page I receive on error is still the same "Internal Server Error".

What's my error?

Answer 1

error_page handles errors that are generated by nginx. By default, nginx will return whatever the proxy server returns regardless of http status code.

What you're looking for is proxy_intercept_errors

This directive decides if nginx will intercept responses with HTTP status codes of 400 and higher.

By default all responses will be sent as-is from the proxied server.

If you set this to on then nginx will intercept status codes that are explicitly handled by an error_page directive. Responses with status codes that do not match an error_page directive will be sent as-is from the proxied server.