How can I make Nginx return HTTP 503 when my proxied app server is down?

I have an nginx web server sitting in front of a Jetty Java app server running a web application.

I'd like to configure nginx to return a HTTP 503 if the proxied Jetty server is down.

This way when I bring the app server down for maintenance, of if it happens to crash, a 503 is returned to any clients letting them know the site is temporarily unavailable.

However, with the basic configuration, Nginx returns a HTTP 502 Bad Gateway when it can't connect to the proxy_pass location.

Is it possible to configure nginx to report a 503 instead?

You can do so by setting an error page.

error_page 502 =503 /maintenance.html

With just the contents of Martin Fjordvald's answer I was still getting 502, I didn't have a real maintenance.html page, but this seems to work:

    location / {
        error_page 502 =503 /maintenance.html;
        include proxy_params;
        proxy_pass http://unix:/var/run/my.sock;
    }
    location /maintenance.html {
        return 503;
    }