AWS SDK for Ruby
Developer Guide

Working with a Dead Letter Queue in Amazon SQS

Amazon SQS provides support for dead letter queues. A dead letter queue is a queue that other (source) queues can target for messages that can't be processed successfully. You can set aside and isolate these messages in the dead letter queue to determine why their processing didn't succeed. For more information about dead letter queues, see Using Amazon SQS Dead Letter Queues.

In this example, you use the AWS SDK for Ruby with Amazon SQS to:

  1. Create a queue that represents a dead letter queue by using Aws::SQS::Client#create_queue.

  2. Associate the dead letter queue with an existing queue by using Aws::SQS::Client#set_queue_attributes.

  3. Send a message to the existing queue by using Aws::SQS::Client#send_message.

  4. Poll the queue by using Aws::SQS::QueuePoller.

  5. Receive messages in the dead letter queue by using Aws::SQS::Client#receive_message.

Prerequisites

Before running the example code, you need to install and configure the AWS SDK for Ruby, as described in:

You also need to use the AWS Management Console to create the existing queue, my-queue.

Note

For the sake of simplicity, this example code doesn't demonstrate Aws::SQS::Client#add_permission. In a real-world scenario, you should always restrict access to actions such as SendMessage, ReceiveMessage, DeleteMessage, and DeleteQueue. Not doing so could cause information disclosure, denial of service, or injection of messages into your queues.

Example

require 'aws-sdk-sqs' # v2: require 'aws-sdk' # Uncomment for Windows. # Aws.use_bundled_cert! sqs = Aws::SQS::Client.new(region: 'us-east-1') # Create a queue representing a dead letter queue. dead_letter_queue_name = "dead-letter-queue" sqs.create_queue({ queue_name: dead_letter_queue_name }) # Get the dead letter queue's URL and ARN, so that you can associate it with an existing queue. dead_letter_queue_url = sqs.get_queue_url(queue_name: dead_letter_queue_name).queue_url dead_letter_queue_arn = sqs.get_queue_attributes({ queue_url: dead_letter_queue_url, attribute_names: ["QueueArn"] }).attributes["QueueArn"] # Associate the dead letter queue with an existing queue. begin queue_name = "my-queue" queue_url = sqs.get_queue_url(queue_name: queue_name).queue_url # Use a redrive policy to specify the dead letter queue and its behavior. redrive_policy = { "maxReceiveCount" => "5", # After the queue receives the same message 5 times, send that message to the dead letter queue. "deadLetterTargetArn" => dead_letter_queue_arn }.to_json sqs.set_queue_attributes({ queue_url: queue_url, attributes: { "RedrivePolicy" => redrive_policy } }) rescue Aws::SQS::Errors::NonExistentQueue puts "A queue named '#{queue_name}' does not exist." exit(false) end # Send a message to the queue. puts "Sending a message..." sqs.send_message({ queue_url: queue_url, message_body: "I hope I get moved to the dead letter queue." }) 30.downto(0) do |i| print "\rWaiting #{i} second(s) for sent message to be receivable..." sleep(1) end puts "\n" poller = Aws::SQS::QueuePoller.new(queue_url) # Receive 5 messages max and stop polling after 20 seconds of no received messages. poller.poll(max_number_of_messages:5, idle_timeout: 20) do |messages| messages.each do |msg| puts "Received message ID: #{msg.message_id}" end end # Check to see if Amazon SQS moved the message to the dead letter queue. receive_message_result = sqs.receive_message({ queue_url: dead_letter_queue_url, max_number_of_messages: 1 }) if receive_message_result.messages.count > 0 puts "\n#{receive_message_result.messages[0].body}" else puts "\nNo messages received." end

On this page: