diff --git a/app/assets/javascripts/cable.js b/app/assets/javascripts/cable.js
index 2fb3e843..0edb4a6e 100644
--- a/app/assets/javascripts/cable.js
+++ b/app/assets/javascripts/cable.js
@@ -6,7 +6,11 @@
 //= require_tree ./channels
 
 (function() {
+  var protocol = (window.location.protocol === "https:" ? "wss://" : "ws://");
+  var host = window.GreenLight.WEBSOCKET_HOST || window.location.host + window.GreenLight.RELATIVE_ROOT;
+  var url = protocol + host + '/cable';
+
   this.App || (this.App = {});
 
-  App.cable = ActionCable.createConsumer();
+  App.cable = ActionCable.createConsumer(url);
 }).call(this);
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index dc4ff6a3..a47ada99 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -18,6 +18,12 @@ class ApplicationController < ActionController::Base
   end
   helper_method :user_name_limit
 
+  # Relative root helper (when deploying to subdirectory).
+  def relative_root
+    Rails.configuration.relative_url_root || ""
+  end
+  helper_method :relative_root
+
   # Determines if the BigBlueButton endpoint is configured (or set to default).
   def bigbluebutton_endpoint_default?
     return false if loadbalanced_configuration?
diff --git a/app/views/layouts/application.html.erb b/app/views/layouts/application.html.erb
index 42fbcb9a..0883f47a 100644
--- a/app/views/layouts/application.html.erb
+++ b/app/views/layouts/application.html.erb
@@ -6,6 +6,13 @@
 
     <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.0.13/css/all.css" integrity="sha384-DNOHZ68U8hZfKXOrtjWvjxusGo9WQnrNx2sqG0tfsghAvtVlRW3tvkXWZh58N9jp" crossorigin="anonymous">
 
+    <!-- Global javascript variables and helpers. -->
+    <script type="text/javascript">
+      window.GreenLight = {};
+      window.GreenLight.WEBSOCKET_HOST = "<%= ENV['WEBSOCKET_HOST'] %>"
+      window.GreenLight.RELATIVE_ROOT = "<%= relative_root %>"
+    </script>
+
     <%= stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track': 'reload' %>
     <%= javascript_include_tag 'application', 'data-turbolinks-track': 'reload' %>
   </head>