The other day I noticed a problem on our beta server (let’s call it qa.ourapplication.it): Some controllers were redirecting to production (let’s call it www.ourapplication.com).

This happened due to fact that entire Rails application was hardcoding *_url (like root_url, welcome_url, …) and I’ve replace them to be *_path (like root_path, welcome_path,…).

This should not be an issue for Rails application as long as default_url_options host is set to correct location. So let’s have a look:

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  # ...

  def default_url_options
    case Rails.env
    when 'production'
      { host: 'www.ourapplication.com' }
    when 'qa'
      { host: 'qa.ourapplication.it' }
    # ...
    else
      { host: 'localhost:3000' }
    end
  end

  # ...
end

http://apidock.com/rails/ActionController/Base/default_url_options

Note: Configuring this in a controller is ok but better practice to configure it in config/enviroments/qa.rb like config.action_controller.default_url_options = { host: 'qa.ourapplication.it' }. Or if you really want to have it in a controller, configure config.x.app_host =‘qa.ourapplication.it’ and in ApplicationController let method default_url_options to return hash like { host: Rails.application.config.x.app_host }

Looks ok to me.

So lets have a look into NginX config:

upstream ourapplication {
  server unix:///shared/sockets/ourapplication.sock;
}

server {
  listen                80;
  server_name           www.ourapplication.com qa.ourapplication.it;
  root                  /app/public;

  # ...

  location / {

    proxy_set_header  Host $host;
    proxy_set_header  X-Real-IP $remote_addr;
    proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header  X-Forwarded-Host $server_name;
    proxy_set_header  Client-IP $remote_addr;
    proxy_pass        http://ourapplication;
  }

  # ...

So all should be good ! What is happening here ?

Lets do some debugging and print out the entire request.inspect to the Rails logs to see what’s happening

class WelcomeController < ApplicationController
  # ...
  def index
    Rails.logger.info request.inspect

    # ...
  end
  # ...
end

tail -f log/qa.log

Note: If you use Docker + Nginx + Puma and if you need to debug running docker container, you don’t have to deploy new image or commit running container with a change in a file. All you have to do is get inside running docker container , (sudo docker ps; sudo docker exec -it 1234MyContainerId bash) and once inside do a file change and then run pumactl restart that will reload Puma workers with file change without killing Docker container.

…and this is what popped out (inside qa.ourapplication.it):

# ...
"HTTP_HOST"=>"qa.ourapplication.it", "HTTP_X_REAL_IP"=>"81.11.111.148",
"HTTP_X_FORWARDED_FOR"=>"81.11.111.148",
"HTTP_X_FORWARDED_HOST"=>"www.ourapplication.com",
"HTTP_CLIENT_IP"=>"81.91.247.148", "HTTP_CONNECTION"=>"close", "HTTP_USER_A
# ...
@delete_cookies={},
@host="www.ourapplication.com",
@secure=false,
# ...

Look at the HTTP_X_FORWARDED_HOST

This make sense, X-Forwarded-Host is being passed for the first server of our NginX configuration www.ourapplication.com and Rails is using this header to change the default host.

http://calvincorreli.com/2005/12/05/what-s-with-http_x_forwarded_host/comment-page-1/

Solution

So either remove proxy_set_header X-Forwarded-Host $server_name; if you don’t necessarily need header HTTP_X_FORWARDED_HOST, or extract servers to individual blocks and include commonalities like this:

upstream ourapplication {
  server unix:///shared/sockets/ourapplication.sock;
}

server {
  listen                80;
  server_name           www.ourapplication.com:

  include /etc/nginx/includes/ourapp-redirects;
  include /etc/nginx/includes/ourapp-rootlocation;
}

server {
  listen                80;
  server_name           qa.ourapplication.it:

  include /etc/nginx/includes/ourapp-redirects;
  include /etc/nginx/includes/ourapp-rootlocation;
}

This way you will ensure proper server_name block gets triggered and therefore proper host passed as HTTP_X_FORWARDED_HOST