NGINX not responding - nginx

Question

I have three sites configured on my server using NGINX and the first two are working fine. One is a static site and one is running Rails (using Unicorn). I have attempted to mirror the NGINX/Unicorn configurations.
For the non-working site, I get "problem loading site" in my browser and absolutely nothing in my NGINX error logs (even at debug level) or my Unicorn log. I also get nothing when I attempt to cURL to the site.
I have double checked DNS by pinging domain name and am running out of ideas. I've also tried making this the default server and browsing by IP address.
Thoughts on how I should go about debugging? I would like to at least understand if NGINX is seeing these requests or not.
NGINX configuration:
upstream unicorn-signup {
server unix:/home/signup/app/tmp/sockets/unicorn.sock;
}
server {
listen 80;
listen [::]:80;
root /home/signup/app/current/public;
server_name signup.quote2bill.com;
# configure for Unicorn (NGINX acts as reverse proxy)
location / {
try_files $uri #unicorn;
}
location #unicorn {
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_set_header X-Forwarded_Proto $scheme;
proxy_redirect off;
proxy_pass http://unicorn-signup;
proxy_read_timeout 300s;
proxy_send_timeout 300s;
}
}

Answer 1

Fixed! It was the dreaded force_ssl flag in my production configuration. For future travelers, here is how I went about troubleshooting:
Went on a Costco run to clear my mind and buy huge quantities of stuff.
To determine if it was a DNS, NGINX or Unicorn/Rails problem, I replaced my NGINX configuration with a very simple one and placed a simple index.html in my public root. This worked fine - which lets DNS off the hook (I could resolve the domain name at the web server).
I diff'd the working and non-working NGINX configuration files for the nth time and made them as close as possible but didn't find anything.
Then I noticed that when I was serving the simple index.html file in #2 above, the domain was not getting redirected to https:// but when switched to my "normal" Unicorn/Rails version, I was always getting redirected.
I searched for Rails redirecting to SSL and remembered the force_ssl flag.
I checked my two projects and noticed the flag was not set in the working project, but set in the non-working one (smoking gun).
I changed, committed, redeployed and reloaded the browser and it... didn't work (!) Fortunately, I had the good sense to clear browser cache and try again and it is all good now.
Hope this helps someone.