Exam AWS Certified Developer - Associate DVA-C02 topic 1 question 60 discussion

B. Create and inspect the Lambda dead-letter queue. Troubleshoot the failed functions. Reprocess the events. When Lambda functions are invoked asynchronously, there is a possibility that the function fails without logging errors if there is no proper error handling. Configuring a dead-letter queue (DLQ) allows you to capture and review events that were not processed successfully. By creating and inspecting the DLQ, you can identify and troubleshoot the issues with the failed Lambda invocations and reprocess those events if needed. This will help ensure that no orders are missed without leaving any errors in the Lambda logs.

Explanation: By configuring a dead-letter queue (DLQ) for the Lambda function, you can capture asynchronous invocation events that were not successfully processed. This allows you to troubleshoot the failed functions and reprocess the events, ensuring that orders are not missed. The DLQ will hold information about the failed events, allowing you to analyze and resolve the issue.

Option A is obviously wrong. Remember, it's an asynchronous labmda, so replaying the POST API returns no info instrumental to issue diagnosis. If you know how AWS usually designs a quiz, you'll know B is definitely the answer.

B is the correct answer.

https://aws.amazon.com/about-aws/whats-new/2016/12/aws-lambda-supports-dead-letter-queues/

B. Crie e inspecione a fila de mensagens mortas do Lambda. Solucione os problemas das funções com falha. Reprocesse os eventos. Mais Votados

The Lambda application logs show no errors or failures. - So Lambda function was not invoked at all

The Lambda Dead Letter Queue is a feature that helps in troubleshooting events that failed processing by a Lambda function. When an asynchronous invocation of a Lambda function fails, AWS Lambda can direct the failed event to an Amazon SNS topic or an Amazon SQS queue (the dead-letter queue), where the event is stored and can be analyzed or reprocessed.

I don't like B which has reprocess the errors, which will make a whole load of errors be process creating orders which could be months old

B https://aws.amazon.com/what-is/dead-letter-queue/

A) asynchronous invocations doe not return result to the caller, thus I do not expect errors in frontend log C) the scenario question rules out the option to have error messages in the Lambda log D) I do not see how caching can have impact in this scenario B) having a dead-letter queue is a viable option to troubleshoot asynchronous lambda invocation error, another option would be using Destination

Option C is the appropriate choice because it involves inspecting the Lambda logs in Amazon CloudWatch to identify any potential issues or errors that might be causing the orders not to be processed Option B is not the most appropriate choice because the dead-letter queue is generally used to capture events that cannot be processed by a Lambda function. In this scenario, it seems that the Lambda function is executing without apparent errors. Thus, the issue might not be related to dead-letter queue failures.

I think D should be the correct answer to this question. The logs have no indications of errors or failed events, so if some transactions are not being processed, that probably means that the lambda function wasn't invoked for those calls. One reason could be that caching is enabled in API gateway for the POST request, so the lambda function isn't triggered for any cache hits. - A is not correct as the frontend would be getting 202s for all asynchronous post requests. - B is not correct because lambda logs have no errors => no lambda execution errors => DLQ won't get any requests of interest if we enable it. A comment below mentioned that asynchronous lambda invocations don't generate logs, but that is not true. - C is obviously incorrect. The premise explicitly mentions that there aren't any errors in the logs.

https://aws.amazon.com/about-aws/whats-new/2016/12/aws-lambda-supports-dead-letter-queues/

It's B. Apparently C & D are wrong. Also it's not A because the call is async. Meaning that the response code from the lambda service is 202. Since generally frontend can make POST requests, the problem should be visible somewhere in the backed. Dead-letter queues are for debugging and further analysis. Hence should be B.

Ans: B B. Create and inspect the Lambda dead-letter queue. Troubleshoot the failed functions. Reprocess the events. Since the Lambda application logs show no errors or failures, it is possible that the asynchronous invocation is not being processed successfully. In this case, the best solution would be to inspect the Lambda dead-letter queue, which stores failed asynchronous invocations. By doing this, the developer can troubleshoot any failed functions and reprocess the events.

A The Lambda function might have not been called since the Lambda logs show no errors or failures. The cause might be that the frontend application does not call the API or an error occurs in the API Gateway processing.