Configure connection pools for ActionCable

Use ActionCable's worker pool size to determine connection pool size

cable/config.ru

@@ -3,4 +3,6 @@
 require ::File.expand_path('../../config/environment', __FILE__)
 Rails.application.eager_load!
 
+ACTION_CABLE_SERVER = true
+
 run ActionCable.server

config/gitlab.yml.example

@@ -1065,6 +1065,11 @@ production: &base
     #   host: localhost
     #   port: 3808
 
+  ## ActionCable settings
+  action_cable:
+    # Number of threads used to process ActionCable connection callbacks and channel actions
+    # worker_pool_size: 4
+
   ## Monitoring
   # Built in monitoring settings
   monitoring:

config/initializers/1_settings.rb

@@ -717,6 +717,12 @@ Settings.webpack.dev_server['enabled'] ||= false
 Settings.webpack.dev_server['host']    ||= 'localhost'
 Settings.webpack.dev_server['port']    ||= 3808
 
+#
+# ActionCable settings
+#
+Settings['action_cable'] ||= Settingslogic.new({})
+Settings.action_cable['worker_pool_size'] ||= 4
+
 #
 # Monitoring settings
 #

config/initializers/actioncable.rb → config/initializers/action_cable.rb

@@ -5,4 +5,5 @@ Rails.application.configure do
   # we're running ActionCable as a standalone server
   config.action_cable.mount_path = nil
   config.action_cable.url = Gitlab::Utils.append_path(Gitlab.config.gitlab.relative_url_root, '/-/cable')
+  config.action_cable.worker_pool_size = Gitlab.config.action_cable.worker_pool_size
 end

lib/gitlab/runtime.rb

@@ -37,7 +37,7 @@ module Gitlab
       end
 
       def puma?
-        !!defined?(::Puma)
+        !!defined?(::Puma) && !defined?(ACTION_CABLE_SERVER)
       end
 
       # For unicorn, we need to check for actual server instances to avoid false positives.
@@ -70,25 +70,31 @@ module Gitlab
       end
 
       def web_server?
-        puma? || unicorn?
+        puma? || unicorn? || action_cable?
+      end
+
+      def action_cable?
+        !!defined?(ACTION_CABLE_SERVER)
       end
 
       def multi_threaded?
-        puma? || sidekiq?
+        puma? || sidekiq? || action_cable?
       end
 
       def max_threads
         main_thread = 1
 
-        if puma?
-          Puma.cli_config.options[:max_threads] + main_thread
+        if action_cable?
+          Gitlab::Application.config.action_cable.worker_pool_size
+        elsif puma?
+          Puma.cli_config.options[:max_threads]
         elsif sidekiq?
           # An extra thread for the poller in Sidekiq Cron:
           # https://github.com/ondrejbartas/sidekiq-cron#under-the-hood
-          Sidekiq.options[:concurrency] + main_thread + 1
+          Sidekiq.options[:concurrency] + 1
         else
-          main_thread
-        end
+          0
+        end + main_thread
       end
     end
   end

spec/lib/gitlab/runtime_spec.rb

@@ -105,4 +105,17 @@ describe Gitlab::Runtime do
 
     it_behaves_like "valid runtime", :rails_runner, 1
   end
+
+  context "action_cable" do
+    before do
+      stub_const('ACTION_CABLE_SERVER', true)
+      stub_const('::Puma', Module.new)
+
+      allow(Gitlab::Application).to receive_message_chain(:config, :action_cable, :worker_pool_size).and_return(8)
+    end
+
+    it "reports its maximum concurrency based on ActionCable's worker pool size" do
+      expect(subject.max_threads).to eq(9)
+    end
+  end
 end