Merge branch '352250-fix-puma-crash-redis' into 'master'

Restart Action Cable server when Redis disconnects

See merge request gitlab-org/gitlab!80822

config/initializers/action_cable.rb

@@ -10,6 +10,7 @@ Rails.application.configure do
 end
 
 ActionCable::SubscriptionAdapter::Base.prepend(Gitlab::Patch::ActionCableSubscriptionAdapterIdentifier)
+ActionCable::SubscriptionAdapter::Redis::Listener.prepend(Gitlab::Patch::ActionCableRedisListener)
 
 # https://github.com/rails/rails/blob/bb5ac1623e8de08c1b7b62b1368758f0d3bb6379/actioncable/lib/action_cable/subscription_adapter/redis.rb#L18
 ActionCable::SubscriptionAdapter::Redis.redis_connector = lambda do |config|

lib/gitlab/patch/action_cable_redis_listener.rb

+# frozen_string_literal: true
+
+# Modifies https://github.com/rails/rails/blob/v6.1.4.6/actioncable/lib/action_cable/subscription_adapter/redis.rb
+# so that it is resilient to Redis connection errors.
+# See https://github.com/rails/rails/issues/27659.
+
+# rubocop:disable Gitlab/ModuleWithInstanceVariables
+module Gitlab
+  module Patch
+    module ActionCableRedisListener
+      private
+
+      def ensure_listener_running
+        @thread ||= Thread.new do
+          Thread.current.abort_on_exception = true
+
+          conn = @adapter.redis_connection_for_subscriptions
+          listen conn
+        rescue ::Redis::BaseConnectionError
+          @thread = @raw_client = nil
+          ::ActionCable.server.restart
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/patch/action_cable_redis_listener_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Patch::ActionCableRedisListener do
+  let(:adapter) { instance_double('ActionCable::SubscriptionAdapter::Redis') }
+  let(:connection) { instance_double('Redis') }
+  let(:listener) { ActionCable::SubscriptionAdapter::Redis::Listener.new(adapter, nil) }
+
+  before do
+    allow(Thread).to receive(:new).and_yield
+    allow(adapter).to receive(:redis_connection_for_subscriptions).and_return(connection)
+  end
+
+  it 'catches Redis connection errors and restarts Action Cable' do
+    expect(connection).to receive(:without_reconnect).and_raise Redis::ConnectionError
+    expect(ActionCable).to receive_message_chain(:server, :restart)
+
+    expect { listener.add_channel('test_channel', nil) }.not_to raise_error
+  end
+
+  it 're-raises other exceptions' do
+    expect(connection).to receive(:without_reconnect).and_raise StandardError
+    expect(ActionCable).not_to receive(:server)
+
+    expect { listener.add_channel('test_channel', nil) }.to raise_error(StandardError)
+  end
+end