I have an SQS queue linked to a deadletter queue via a redrive policy. Terraform sample:
redrive_policy = jsonencode({
deadLetterTargetArn = aws_sqs_queue.deadletter_queue.arn
maxReceiveCount = 10
})
The queue processing is implemented with exponential backoff. If processing is successful the message is simply deleted. If processing fails it retries with an initial VisibilityTimeout of 30 seconds, which doubles each time, the final retry timeout (between 9th and 10th attempt) is roughly 2 hours.
My question is, after the final retry, when does the message get sent to the deadletter queue? Immediately after the 10th attempt or does it have to wait out the VisibilityTimeout (of about 4 hours)?.
My concern is that it seems redundant to put a visibility timeout on a message if it's just going to be sent straight to the deadletter - this delays alerts for example.
If you have 4 hour visibility timeout, after 10 th attempt SQS will have to wait 4 hours before it can deem the attempt unsuccessfully. SQS can't assume that the attempt failed after 1 minute, if it may take 4 hours to process the message. SQS does not know what are you doing with the messages and has no means of checking if your application failed to process the message before visibility timeout expires.
Lets say you are running 2 consumers, A and B.
Visibility timeout is a time period which start right after "consumer A" receives the message. For this duration, "consumer B" is not able to receive the message (message is reserved for the "consumer A"). So visibility timeout's purpose is to "hide" message from other consumers to avoid duplication, while one of the consumers already working on it (also see aws doc here).
About the question, after the final retry, message is immediately moved to dead letter queue. It doesn't wait for a visibility timeout to be over, because it won't have the chance to be consumed again. Message is moved to dead letter queue and removed from source queue.
Related
My application consists of:
1 Amazon SQS message queue
n workers
The workers have the following logic:
1. Wait for message from SQS queue
2. Perform task described in message
3. Delete the message from the SQS queue
4. Go to (1)
I want each message to be received by only one worker to avoid redundant work.
Is there a mechanism to mark a message as "in progress" using SQS, so that other pollers do not receive it?
Alternatively, is it appropriate to delete the message as soon as it is received?
1. Wait for message from SQS queue
2. Delete the message from the SQS queue
3. Perform task described in message
4. Go to (1)
If I follow this approach, is there a way to recover received but unprocessed messages in case a worker crashes (step (3) fails)?
This question is specific to Spring, which contains all sorts of magic.
An SQS message is considered to be "inflight" after it is received from a queue by a consumer, but not yet deleted from the queue. These messages are not visible to other consumers.
In SQS messaging, a message is considered in "inflight" if:
You the consumer have received it, and
the visibility timeout has not expired and
you have not deleted it.
SQS is designed so that you can call ReceiveMessage and a message is given to you for processing. You have some amount of time (the visibility timeout) to perform the processing on this message. During this "visibility" timeout, if you call ReceiveMessage again, no worker will be returned the message you are currently working with. It is hidden.
Once the visibility timeout expires the message will be able to be returned to future ReceiveMessage calls. This could happen if the consumer fails in some way. If the process is successful, then you can delete the message.
The number of messages that are hidden from ReceiveMessage call is the "inflight" number. Currently a SQS queue is set by default to allow a max of 120,000 messages to be "inflight".
http://docs.amazonwebservices.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/AboutVT.html
There will be ReciepientHandle String which will be sent with the message. It will be having a expiry time based on queue visibility timeout.
You can use the this ReciepientHandle to delete message from queue
I have seen an option called visibility timeout in AWS SQS which sets a time for other consumers to ignore the message which is being processed by one.
Is there an option to set a time before the message actually becomes available for consumers to use it, may be set while message actually is inserted into Queue
There is such an option, but it is a queue-level option, not a message-level option:
You can use the CreateQueue action to create a delay queue by setting the DelaySeconds attribute to any value between 0 and 900 (15 minutes). You can also change an existing queue into a delay queue using the SetQueueAttributes action to set the queue's DelaySeconds attribute
http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-delay-queues.html
When the value is nonzero, all messages are delayed by the specified number of seconds before they are initially visible to any consumer.
Found an option called Amazon SQS Message Timers
Amazon SQS message timers allow you to specify an initial invisibility period for a message that you add to a queue. For example, if you send a message with the DelaySeconds parameter set to 45, the message isn't visible to consumers for the first 45 seconds during which the message stays in the queue.
The default value for DelaySeconds is 0.
To set a delay period that applies to all messages in a queue, use delay queues. A message timer setting for an individual message overrides any DelaySeconds value that applies to the entire delay queue.
For more info on SQS check this detailed PDF by AWS
When you are processing the message, you can actually use ChangeMessageVisibility() . This allows you to change the timeout period while holding the message either up or down. For example, if you KNOW that your message failed the first time, you can set it to 0 and it will put it back on the queue. If you wanted a specifically longer timeout, you could check for that type of message and set it to 10 minutes for example.
I set visibility time out 12 hours and max message 3, delay time 15 min, I'm get sqs message few minute after automatically I get same message again.
Why do I get multiple sqs message without timeout?
After visibility time out it delete message in queue or send again sqs message?
When ReceiveMessage() is called on an Amazon SQS queue, up to 10 messages (configurable) will be retrieved from the queue.
These messages will be marked as Invisible or In-Flight. This means that the messages are still in the queue, but will not be returned via another ReceiveMessage() call. The messages will remain invisible for a period of time. The default period is configured on the queue ("Default Visibility Timeout") or when the messages are retrieved (VisibilityTimeout).
When an application has finished handling a message, it should call DeleteMessage(), passing the MessageHandle that was provided with the message. The message will then be deleted from the queue.
If the invisibility period expires before a message is deleted, it will be placed on the queue again and applications can retrieve it again. Therefore, be sure to set your invisibility timeout to be longer than an application normally takes to process a message.
It is possible that a message may be retrieved more than once from Amazon SQS. It is rare, but can happen where there are multiple processes retrieving messages simultaneously. Thus, SQS is "At least once delivery". If this is a problem, you can use FIFO Queues (not yet available in every region) that will guarantee that each message is delivered only once, but there are throughput restrictions on FIFO queues.
So, if you are receiving a message more than once:
You should check your invisibility timeout setting (both the default setting and the value that can be passed when you call ReceiveMessage())
Consider using FIFO queues
Have your application check whether a message has already been processed before processing it again (eg via a unique ID)
I have an Amazon SQS Queue and I am trying to make it work this way:
When a new message added to the queue, only the first client who received that message will start work
For others, the message will be invisible for period of time
Is it possible to do this using Visibility Timeout?
When a consumer receives and processes a message from SQS queue, the message still remains in the queue (until it is deleted by the consumer). To make sure that other consumers don't process the same message, you can set visibility timeout of the queue. Once the message has been processed by the consumer, you can delete the message from the queue. For the duration of the visibility timeout, no other consumer will be able to receive and process the same message.
There is no other way to "lock" the message except setting a long Visibility Timeout, with a maximum 12 hour timeout.
However, if your real concern also including error/crashing, you can make use of the Dead-Letter-Queue redrive policy, to deal with queue contents that fail to be process indefinitely.
What is the meaning of "Visibility Timeout" for Amazon SQS service ? What factors determine an ideal value for this field ?
I have looked at http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/Welcome.html
When using sqs as queuing service, when you read the message off the queue it does not automatically delete the message off the queue.
So when you are processing the message, sqs will wait for the time period defined as visibility timeout before other consumers will get the same message again.
The best time value to set for the visibility timeout will be at least the timeout value for the consumer process. If the consumer is able to successfully complete the processing then it would delete the message off the queue else if it times out then the message reappears in the queue for other consumer to pick it again.
Visibility timeout is the time-period or duration you specify for the queue item which when is fetched and processed by the consumer is made hidden from the queue and other consumers.
The main purpose is to avoid multiple consumers (or the same consumer), consuming the same item repetitively.
The key factor to be considered while arriving at this value is the time & effort taken by the consumer(s) to process a single queue item.
Basically the time taken by the consumer to process the message. And during the same time the message is unvailable for any other consumer (since this is a distributed system). Although the time priod is configurable, the default visibility timeout for a message is 30 seconds. The minimum is 0 seconds. The maximum is 12 hours.
https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-visibility-timeout.html
Visibility Timeout is an important functionality of Amazon SQS. It helps to ensure the integrity and reliability of message processing in distributed systems.
You can know more about it here https://link.medium.com/u3A8aId0Swb