Rails Subdomain Routing

Question

I'm trying to setup subdomain routing for an admin page. Yet when using admin.localhost I'm able to route to the subdomain just fine. When I use lvh.me I'm routed to the correct home page, although when using admin.lvh.me I'm routing to the same home page and not the admin login page.

# config/routes.rb  
constraints(AdminSubdomain) do
constraints subdomain: 'admin' do

  devise_for      :admins

  devise_scope    :admin do
    authenticated :admin do
      root to: 'admin_home#index', as: :authenticated_root
    end
    unauthenticated do
      root to: 'devise/sessions#new', as: :unauthenticated_root
    end
  end

  resources       :example
  resources       :example

 end
end

Other routing subdomain parameters I've tried

module: "admin", path: "/", constraints: lambda { |r| r.subdomain.split('.')[0] == 'admin' } do
  [...] # Additional routes
end

and

constraints subdomain: 'admin' do
  [...] # Additional routes
end

Then for for the AdminSubdomain class

# lib/admin_subdomain.rb
class AdminSubdomain
  def self.matches?(request)
   case request.subdomain
   when 'admin'
    true
   else
    false
   end
  end
 end

I've also tried variations on the admin_subdomain.rb

# lib/admin_subdomain.rb
class AdminSubdomain
  def self.matches?(request)
   case request.subdomain
   when 'www', '', nil
    true
   else
    false
   end
  end
 end

Then wrapping the admin_subdomain class like so:

# config/routes.rb
constraints(AdminSubdomain) do
  constraints subdomain: 'admin' do
    [...] # routes same as above
  end
 end

All non-subdomain pages aren't covered by routing constraint, I first realized the problem during a staging deploy. When I encountered the same problem of not linking to the correct subdomain. This is when I believed it might be the NGINX proxy running a muck.

# NGINX.conf {appname} == actual name
upstream puma {
  server    unix:///home/deploy/{appname}/shared/tmp/sockets/{appname}-puma.sock;
 }

 server {
   listen 80;
   listen [::]:80;

   # server_name localhost;

   root /home/deploy/{appname}/current/public;
   access_log /home/deploy/{appname}/current/log/nginx.access.log;
   error_log /home/deploy/{appname}/current/log/nginx.error.log info;

   location ^~ /assets/ {
     gzip_static on;
     expires max;
     add_header Cache-Control public;
   }

   try_files $uri/index.html $uri @puma;
   location @puma {
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
     proxy_set_header Host $http_host;
     proxy_redirect off;

     proxy_pass http://puma;
   }

   error_page 500 502 503 504 /500.html;
   client_max_body_size 10M;
   keepalive_timeout 10;
  }

I've tried multiple nginx configs including adding

# wildcard nginx server_name
server_name example.com *.example.com;

# localhost server_name
server_name localhost;

and just commenting out server_name altogether as you can see above in the nginx.conf

When I run 'rake routes' I get:

I thought this might be a dev-env/staging-env issue, after looking through other stack questions, I've added:

# development.rb (added)
config.action_dispatch.tld_length = 0

# staging.rb (added)
config.action_dispatch.tld_length = 2

I can't seem to figure out what I'm doing wrong as nothing seems to be working correctly, and I've just started doing what I like to call 'variation circles.'

Resources Checked:

How to access subdomains

Rails tutorial for subdomains

Devise specific subdomain routing

Subdomain NameSpace Error

Rails subdomain redirection

Devise subdomain routes rails 4

Project Specifications:

rails version: 5.0.0.1

ruby version: 2.3.0

puma version: 3.6.2

devise version: 4.2.0

Utilizing ActiveRecord

I've been working with RoR for about 3 months now, and have been able to sort my way though most issues. I'm 3 days deep into fixing this subdomain issue and I can't seem to determine the problem.