Build queue_url without database when maintenance mode is enabled

app/models/barbeque/job_queue.rb

@@ -13,4 +13,27 @@ class Barbeque::JobQueue < Barbeque::ApplicationRecord
   def sqs_queue_name
     SQS_NAME_PREFIX + name
   end
+
+  # Returns queue URL of given name.
+  # Basically, we should use stored queue URL as the documentation[1] suggests.
+  # But when the Barbeque's database is temporarily unavailable due to
+  # scheduled maintenance, we have to build queue URL without the database. The
+  # maintenance mode is enabled by BARBEQUE_DATABASE_MAINTENANCE and
+  # AWS_ACCOUNT_ID variable.
+  # [1]: http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-queue-message-identifiers.html#sqs-general-identifiers
+  #
+  # @param name [String] queue name in Barbeque
+  # @return [String] queue URL of SQS
+  def self.queue_url_from_name(name)
+    if database_maintenance_mode?
+      "https://sqs.#{ENV.fetch('AWS_REGION')}.amazonaws.com/#{ENV.fetch('AWS_ACCOUNT_ID')}/#{SQS_NAME_PREFIX}#{name}"
+    else
+      select(:queue_url).find_by!(name: name).queue_url
+    end
+  end
+
+  def self.database_maintenance_mode?
+    ENV['BARBEQUE_DATABASE_MAINTENANCE'] == '1' && ENV['AWS_REGION'].present? && ENV['AWS_ACCOUNT_ID'].present?
+  end
+  private_class_method :database_maintenance_mode?
 end

app/services/barbeque/message_enqueuing_service.rb

@@ -20,9 +20,9 @@ def initialize(application:, job:, message:, queue: nil)
 
   # @return [String] message_id
   def run
-    queue = Barbeque::JobQueue.find_by!(name: @queue)
+    queue_url = Barbeque::JobQueue.queue_url_from_name(@queue)
     response = Barbeque::MessageEnqueuingService.sqs_client.send_message(
-      queue_url:    queue.queue_url,
+      queue_url:    queue_url,
       message_body: build_message.to_json,
     )
     response.message_id

spec/factories/job_queue.rb

@@ -1,7 +1,7 @@
 FactoryGirl.define do
   factory :job_queue, class: Barbeque::JobQueue do
     sequence(:name) { |n| "queue-#{n}" }
-    sequence(:queue_url) { |n| "https://sqs.ap-northeast-1.amazonaws.com/123456789012/Barbeque-#{n}" }
+    queue_url { "https://sqs.ap-northeast-1.amazonaws.com/123456789012/Barbeque-#{name}" }
     description 'Default queue'
   end
 end

spec/services/message_enqueuing_service_spec.rb

@@ -11,7 +11,7 @@
     let(:send_message_result) { double('Aws::SQS::Types::SendMessageResult', message_id: message_id) }
 
     before do
-      allow(Aws::SQS::Client).to receive(:new).and_return(sqs_client)
+      allow(described_class).to receive(:sqs_client).and_return(sqs_client)
     end
 
     it 'enqueues a message whose type is JobExecution' do
@@ -49,5 +49,29 @@
         }.to raise_error(ActiveRecord::RecordNotFound)
       end
     end
+
+    context 'when database is unavailable' do
+      around do |example|
+        env = ENV.to_h
+        ENV['BARBEQUE_DATABASE_MAINTENANCE'] = '1'
+        ENV['AWS_REGION'] = 'ap-northeast-1'
+        ENV['AWS_ACCOUNT_ID'] = '123456789012'
+        example.run
+        ENV.replace(env)
+      end
+
+      it 'builds queue_url without database' do
+        expect(sqs_client).to receive(:send_message).with(hash_including(queue_url: job_queue.queue_url)).and_return(send_message_result)
+        expect(Barbeque::JobQueue).to_not receive(:connection)
+
+        result = Barbeque::MessageEnqueuingService.new(
+          job: job,
+          queue: job_queue.name,
+          message: message,
+          application: application,
+        ).run
+        expect(result).to eq(message_id)
+      end
+    end
   end
 end