Exam AWS Certified Solutions Architect - Professional topic 1 question 679 discussion

A is correct, https://aws.amazon.com/blogs/compute/managing-aws-lambda-function-concurrency/

I choose C. Let me explain why I don't think A is the right approach: if you set Reserved concurrency to let's say 200, I make myself 2 questions: 1) 800 instances will remain available for other lambdas. How do you guarantee 800 is enough for other lambdas? Perhaps 999 lambdas was answering in a timely manner to all the requests and adding a new lambda will break everything. 2) Assigning 200 Reserved instances to the new Lambda does not guarantee that will be enough for the new Lambda. Maybe it requires 500? So, adding SQS queue resolve both of the problems. Thoughts?

Problem with option D is it will trigger every time a message is received in SQS, which is similar to trigger Lambda function through s3 event notification. If Lambda is designed to process in Batch, then D will be more appropriate, but there will be a risk of Lambda timeout. So A should be a better choice.

A according to this youtube explanation: https://youtu.be/kNtOhcpju6g

A according to this youtube explanation: https://youtu.be/kNtOhcpju6g

I am going to go with A on this one. Reserved concurrency because even with SQS you will still use up the allowed concurrency.

This is what reserved concurrency is for

Straight from Jon Bonso tests and correct answer is A. Explanation: Concurrency is the number of requests that your function is serving at any given time. When your function is invoked, Lambda allocates an instance of it to process the event. When the function code finishes running, it can handle another request. If the function is invoked again while a request is still being processed, another instance is allocated, which increases the function's concurrency. Concurrency is subject to a Regional quota that is shared by all functions in a Region. There are two types of concurrency available: Reserved concurrency – Reserved concurrency creates a pool of requests that can only be used by its function, and also prevents its function from using unreserved concurrency. Provisioned concurrency – Provisioned concurrency initializes a requested number of execution environments so that they are prepared to respond to your function's invocations.

"The objects do not need to be processed in real-time" - SQS gives you the option to process in batches, you can also delay delivery to ensure Lambda isn't swarmed with multiple concurrent executions from the object upload.

Key point, addition of this new Lambda function has no adverse effect on other key Lambda functions? So how does C address that? Only A provides and answer with reserved concurrency

Answer is A. C is wrong because the Lamdba functions which read the message from SQS may scale out to 1000 if hundreds of thousands of upload occur in a very short time. It will impact the other Lamdba functions. Refer to https://docs.aws.amazon.com/lambda/latest/dg/with-sqs.html

C. Configure S3 event notifications to add events to an Amazon SQS queue in a separate account. Create the new Lambda function in the same account as the SQS queue and trigger the function when a message arrives in the queue.

I think A is correct.

I think this is C

C is right - The concurrency space available is common for all the functions in the region. By reserving concurrency for a function we ensure no other function can use that concurrency space. However this limits the ability to use the concurrency from open pool.

C. Configure S3 event notifications to add events to an Amazon SQS queue in a separate account. Create the new Lambda function in the same account as the SQS queue and trigger the function when a message arrives in the queue.

I am going with C