Nginx proxy_pass then try_file - ruby-on-rails

Question

I am setting up a Rails app with nginx in front.
What I want is first to check if the URL makes sense for Rails then serve content of the public folder.
I can't achieve this:
upstream extranet {
server localhost:3000;
}
server {
location / {
try_files #extranet $uri;
root /var/www/extranet/public;
}
location #extranet {
proxy_pass http://extranet;
proxy_read_timeout 90;
proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header X-Forwarded-Ssl on;
proxy_set_header X-Forwarded-Port $server_port;
proxy_set_header X-Forwarded-Host $host;
client_max_body_size 100m;
}
}
I get: *1 rewrite or internal redirection cycle while internally redirecting to "/" error.
It seems like try_files $uri #extranet; works but in my case it feels safer to check the Rails app first because the public folder might change.

Answer 1

try_files checks for the presence of a file on the local file system and cannot respond to the response code from a proxy.
Presumably, the proxy response with a 404 response if the remote page does not exist, which can be intercepted by an error_page statement.
For example:
location / {
proxy_pass http://extranet;
proxy_set_header ...
proxy_set_header ...
proxy_set_header ...
proxy_intercept_errors on;
error_page 404 = #fallback;
}
location #fallback {
root /var/www/extranet/public;
try_files $uri =404;
}
See this document for more.