Maintenance page for nginx based nodejs site - node.js

Question

I want to set up a maintenance page for my site (that visitors would see) but I also want to allow devs a way to still be able to access the site and test things (though this last bit, access for devs, is a request from a project manager... not sure it's the best way to do this as it seems like we should test on a staging server).
The site is nodejs based and runs on an nginx server via a proxy_pass.
The way I would have done this under apache is to permit a get param to be passed in that would allow a dev to circumvent being redirected to the maintenance page. Can't seem to figure out how to do this under nginx with a proxy_pass.
I was able to get everything to redirect to the maintenance page but images and css were broken and would not load. Additionally I could not implement a GET param override.
Any suggestions on how to approach this? The various tutorials around the web and comments here on SO don't seem to work and I suspect it has to do with the proxy_pass usage. Not certain.
*edit: I saw this post on SO but my attempts to implement it ended up with the visitor being redirected to "/maintenance" and getting a server error instead of my maintenance page. Also, it doesn't address overriding the redirect.

Answer 1

This is going be a question of how you decide to filter users. If you can filter access on IP address, cookie, or some other request aspect, then it's possible to use an if directive to redirect/rewrite all other users to the maintenance page. You mention using a GET parameter -- this condition would be an example of that (using $arg_PARAMETER as documented here):
server {
if ($arg_secret != "123456") {
rewrite ^(.*)$ /maintenance$1 break;
}
location /maintenance {
#root directive etc
}
location / {
#proxy_pass directive etc
}
}
Or you could invert the condition and configuration, and only proxy_pass for the condition being true. However, ``if` directives can be problematic (see http://wiki.nginx.org/IfIsEvil) so try before deploying.
As for the issue you've found with images and CSS not loading, you'll need to ensure that these maintenance resources always continue to be served because they were likely being affected by redirection rules as well. An example location directive could be like so:
location ~ /(.*\.css|.*\.jpg) {
root /var/www/maintenance;
}