At this time, we launch a brand new set of APIs for Amazon SQS. These new APIs can help you handle dead-letter queue (DLQ) redrive programmatically. Now you can use the AWS SDKs or the AWS Command Line Interface (AWS CLI) to programmatically transfer messages from the DLQ to their unique queue, or to a customized queue vacation spot, to try to course of them once more. A DLQ is a queue the place Amazon SQS robotically strikes messages that aren’t accurately processed by your client software.
To completely admire how this new API may provide help to, let’s have a fast look again at historical past.
Message queues are an integral a part of fashionable software architectures. They permit builders to decouple companies by permitting asynchronous and message-based communications between message producers and customers. In most techniques, messages are continued in shared storage (the queue) till the buyer processes them. Message queues permit builders to construct purposes which can be resilient to short-term service failure. They assist prioritize message processing and scale their fleet of employee nodes that course of the messages. Message queues are additionally standard in event-driven architectures.
Asynchronous message change will not be new in software architectures. The idea of exchanging messages asynchronously between purposes appeared within the 1960s and was first made standard when IBM launched TCAM for OS/360 in 1972. The overall adoption got here 20 years later with IBM MQ Sequence in 1993 (now IBM MQ) and when Solar Microsystems launched Java Messaging Service (JMS) in 1998, an ordinary API for Java purposes to work together with message queues.
AWS launched Amazon SQS on July 12, 2006. Amazon SQS is a extremely scalable, dependable, and elastic queuing service that “simply works.” As Werner wrote on the time: “Now we have chosen a concurrency mannequin the place the method engaged on a message robotically acquires a leased lock on that message; if the message will not be deleted earlier than the lease expires, it turns into out there for processing once more. Makes failure dealing with quite simple.”
On January 29, 2014, we launched dead-letter queues (DLQ). DLQs provide help to keep away from a message that did not be processed from staying perpetually on prime of the queue, probably stopping different messages within the queue from processing. With DLQs, every queue has an related property telling Amazon SQS what number of occasions a message could also be offered for processing (
maxReceiveCount). Every message additionally has an related obtain counter (
ReceiveCount). Every time a client software picks up a message for processing, the message obtain depend is incremented by 1. When
maxReceiveCount, Amazon SQS strikes the message to your designated DLQ for human evaluation and debugging. You typically affiliate alarms with the DLQ to ship notifications when such occasions occur. Typical causes to maneuver a message to the DLQ are as a result of they’re incorrectly formatted, there are bugs within the client software, or it takes too lengthy to course of the message.
At AWS re:Invent 2021, AWS introduced dead-letter queue redrive on the Amazon SQS console. The redrive addresses the second a part of the failed message lifecycle. It means that you can reinject the message in its unique queue to try processing it once more. After the buyer software is fastened and able to devour the failed messages, you’ll be able to redrive the messages from the DLQ again within the supply queue or a personalized queue vacation spot. It simply requires a few clicks on the console.
At this time, we’re including APIs permitting you to write down purposes and scripts that deal with the redrive programmatically. There is no such thing as a longer a have to have a human clicking on the console. Utilizing the API will increase the scalability of your processes and reduces the chance of human error.
Let’s See It in Motion
To check out this new API, I open a terminal for a command-line solely demo. Earlier than I get began, I make sure that I’ve the most recent model of the AWS CLI. On macOS I enter
brew improve awscli.
I first create two queues. One is the dead-letter queue, and the opposite is my software queue:
# First, I create the dead-letter queue (discover the -dlq I select so as to add on the finish of the queue identify) ➜ ~ aws sqs create-queue --queue-name awsnewsblog-dlq # second, I retrieve the Arn of the queue I simply created ➜ ~ aws sqs get-queue-attributes --queue-url https://sqs.us-east-2.amazonaws.com/012345678900/awsnewsblog-dlq --attribute-names QueueArn # Third, I create the appliance queue. I enter a redrive coverage: submit messages within the DLQ after three supply makes an attempt ➜ ~ aws sqs create-queue --queue-name awsnewsblog --attributes '"RedrivePolicy": ""deadLetterTargetArn":"arn:aws:sqs:us-east-2:012345678900:awsnewsblog-dlq","maxReceiveCount":"three""'
Now that the 2 queues are prepared, I submit a message to the appliance queue:
➜ ~ aws sqs send-message --queue-url https://sqs.us-east-2.amazonaws.com/012345678900/awsnewsblog --message-body "Hey World"
Subsequent, I devour the message, however I don’t delete it from the queue. This simulates a crash within the message client software. Message customers are alleged to delete the message after profitable processing. I set the
maxReceivedCount property to three after I entered the
redrivePolicy. I subsequently repeat this operation thrice to drive Amazon SQS to maneuver the message to the dead-letter queue after three supply makes an attempt. The default visibility timeout is 30 seconds, so I’ve to attend 30 seconds or extra between the retries.
➜ ~ aws sqs receive-message --queue-url https://sqs.us-east-2.amazonaws.com/012345678900/awsnewsblog # wait 30 seconds, # then repeat two occasions (for a complete of three receive-message API calls)
After three processing makes an attempt, the message will not be within the queue anymore:
➜ ~ aws sqs receive-message --queue-url https://sqs.us-east-2.amazonaws.com/012345678900/awsnewsblog "Messages": 
The message has been moved to the dead-letter queue. I test the DLQ to substantiate (discover the queue URL ending with
➜ ~ aws sqs receive-message --queue-url https://sqs.us-east-2.amazonaws.com/012345678900/awsnewsblog-dlq "Messages": [ "MessageId": "fdc26778-ce9a-4782-9e33-ae73877cfcb2", "ReceiptHandle": "AQEBCLtBMoZYVMMq7fUGNHeCliqE3mFXnkuJ+nOXLK1++uoXWBG31nDejCpxElmiBZWfbcfGJrEdKj4P9HJdrQMYDbeSqB+u1ZlB7CYzQBiQps4SEG0biEoubwqjQbmDZlPrmkFsnYgLD98D1XYWk/Ik6Z2n/wxDo9ko9rbZ15izK5RFnbwveNy8dfc6ireqVB1EGbeGkHcweHGuoeKWXEab1ynZWhNqZsQgCR6pWRkgtn59lJcLv4cJ4UMewNzvt7tMHH69GvVjXdYDYvJJI2vj+6RHvcvSHWWhTNT+CuPEXguVNuNrSya8gho1fCnKpVwQre6HhMlLPjY4wvn/tXY7+5rmte9eXagCqLQXaENB2R7qWNVPiWRIJy8/cTf37NLYVzBom030DNJlH9EeceRhCQ==", "MD5OfBody": "b10a8db164e0754105b7a99be72e3fe5", "Body": "Hello World" ]
Now that the setup is prepared, let’s programmatically redrive the message to its unique queue. Let’s assume I perceive why the buyer didn’t accurately course of the message and that I fastened the buyer software code. I take advantage of
start-message-move-task on the DLQ to start out the asynchronous redrive. There’s an optionally available attribute (
MaxNumberOfMessagesPerSecond) to manage the rate of the redrive:
➜ ~ aws sqs start-message-move-task --source-arn arn:aws:sqs:us-east-2:012345678900:awsnewsblog-dlq
I can listing and test standing the of the transfer duties I initiated with
list-message-move-tasks or cancel a working job by calling the
➜ ~ aws sqs list-message-move-tasks --source-arn arn:aws:sqs:us-east-2:012345678900:awsnewsblog-dlq "Outcomes": [ "Status": "COMPLETED", "SourceArn": "arn:aws:sqs:us-east-2:012345678900:awsnewsblog-dlq", "ApproximateNumberOfMessagesMoved": 1, "ApproximateNumberOfMessagesToMove": 1, "StartedTimestamp": 1684135792239 ]
Now my software can devour the message once more from the appliance queue:
➜ ~ aws sqs receive-message --queue-url https://sqs.us-east-2.amazonaws.com/012345678900/awsnewsblog
DLQ redrive APIs can be found in the present day in all business Areas the place Amazon SQS is offered.
Redriving the messages from the dead-letter queue to the supply queue or a customized vacation spot queue generates extra API calls billed primarily based on current pricing (beginning at $zero.40 per million API calls, after the primary million, which is free each month). Amazon SQS batches the messages whereas redriving them from one queue to a different. This makes transferring messages from one queue to a different a easy and low-cost possibility.
To study extra about DLQ and DLQ redrive, test our documentation.
Keep in mind that we stay in an asynchronous world—so ought to your purposes. Get began in the present day and write your first redrive software.