Exam AWS Certified Solutions Architect - Associate SAA-C03 topic 1 question 67 discussion

In case of SQS - multi-consumers if one consumer has already picked the message and is processing, in meantime other consumer can pick it up and process the message there by two copies are added at the end. To avoid this the message is made invisible from the time its picked and deleted after processing. This visibility timeout is increased according to max time taken to process the message

To ensure that messages are being processed only once, a solutions architect should use the ChangeMessageVisibility API call to increase the visibility timeout which is Option D. The visibility timeout determines the amount of time that a message received from an SQS queue is hidden from other consumers while the message is being processed. If the processing of a message takes longer than the visibility timeout, the message will become visible to other consumers and may be processed again. By increasing the visibility timeout, the solutions architect can ensure that the message is not made visible to other consumers until the processing is complete and the message can be safely deleted from the queue. Option A (Use the CreateQueue API call to create a new queue) would not address the issue of duplicate message processing. Option B (Use the AddPermission API call to add appropriate permissions) is not relevant to this issue. Option C (Use the ReceiveMessage API call to set an appropriate wait time) is also not relevant to this issue.

I chose D as well, I understand the rationale behind it.But I think it is named incorrectly. should this not be "InvisibilityTimeout" instead of "VisibilityTimeout"? If the message becomes visible again after a timeout, because SQS assumes it failed processing - then it remains invisible and after timeout it becomes visible again... So thats wheremy point of contention is.

Explicação: Causa provável do problema: O problema ocorre porque o tempo de visibilidade (visibility timeout) configurado na fila do Amazon SQS é muito curto. Quando uma instância EC2 lê uma mensagem da fila e começa a processá-la, se o processamento não for concluído antes que o tempo de visibilidade expire, a mensagem volta para a fila e pode ser processada novamente por outra instância. Isso leva a registros duplicados na tabela RDS.

Visibility timeout is used to manage multiple users.

Ans D - once the message is selected in the queue 'hide' it from other users/apps so it is only processed once, using API 'ChangeMesssageVisibility'

AB: Irrelevant C: This is for long polling not for execution https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-short-and-long-polling.html#sqs-long-polling D: Visibility is correct fix issue because over here other SQS clients are seeing the same message back in the que when the previous processor is taking longer than expected to process the message

I also opt for D, but asking does increasing MessageVisibilityTimeOut good always?

Option D is the right answer.

The visibility timeout is the duration during which SQS prevents other consumers from receiving and processing the same message. By increasing the visibility timeout, you allow more time for the processing of a message to complete before it becomes visible to other consumers. Option A, creating a new queue, does not address the issue of concurrent processing and duplicate records. It would only create a new queue, which is not necessary for solving the problem. Option B, adding permissions, also does not directly address the issue of duplicate records. Permissions are necessary for accessing the SQS queue but not for preventing concurrent processing. Option C, setting an appropriate wait time using the ReceiveMessage API call, does not specifically prevent duplicate records. It can help manage the rate at which messages are received from the queue but does not address the issue of concurrent processing.

D is correct

Answer D: visibility timeout beings when amazon SQS return a message

D = ChangeMessageVisibility

In theory, between reception and changing visibility, you can have multiple consumers. Question is not good as it won't guarantee not executing twice.

Increaseing visibility timeout makes sure message is not visible for time taken to process the message.

Option D

D is correct