Assume that the cable server is running in-process by default, offer option to change that in config/environments/production.rb

actioncable/lib/action_cable/engine.rb

@@ -6,6 +6,8 @@ require "active_support/core_ext/hash/indifferent_access"
 module ActionCable
   class Railtie < Rails::Engine # :nodoc:
     config.action_cable = ActiveSupport::OrderedOptions.new
+    config.action_cable.url = '/cable'
+
     config.eager_load_namespaces << ActionCable
 
     initializer "action_cable.helpers" do

railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt

@@ -40,6 +40,9 @@ Rails.application.configure do
   # config.action_dispatch.x_sendfile_header = 'X-Sendfile' # for Apache
   # config.action_dispatch.x_sendfile_header = 'X-Accel-Redirect' # for NGINX
 
+  # Action Cable should be mounted in a separate process for most production setups
+  # config.action_cable.url = 'wss://example.com/cable'
+
   # Force all access to the app over SSL, use Strict-Transport-Security, and use secure cookies.
   # config.force_ssl = true