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In this section, we are going to do a hands on lab, which is the invoke lambda function asynchronously

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using Amazon S3 to trigger the Lambda function.

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So before we start, let me explain one important topic, which is the Lambda asynchronous invocation.

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So several ADA services, for example, Amazon S3 and Amazon SAS invoke functions asynchronously to

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process the events.

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So basically when we invoke a function asynchronously, we don't wait for a response from the function

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code.

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So how Lambda handles asynchronous invocation?

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You can see the image on the slide.

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Basically client invoke the lambda function asynchronously.

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Lambda queue the events before sending them the function.

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You can see that client invoke lambda function asynchronously, but Lambda has internal event queue

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that stored the events in here and execute after that asynchronously.

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So for asynchronous invocation, Lambda plays the event in a queue and returns a success response without

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additional information.

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A separate process reads the events from the queue and send them into function.

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So in order to invoke a function asynchronously, we should set the invocation type parameter to the

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event so you can see the example command, which is the cli command.

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Invoke lambda function asynchronously.

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You can see in here a w is lambda invoke and we provide the function name.

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The important part is here, which is the invocation type is event.

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That means we invoke these lambda function asynchronously and also the output file could be the response

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JSON, but the output file is one station doesn't contain any information, but it is still created

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when we run this command.

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If Lambda isn't able to add the event to the queue, the error message appear in the command output.

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So you can remember the calculated example at the beginning of the Lambda ClA examples.

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We create lambda function, put a calculator code and invoke calculated lambda function synchronously

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and asynchronously.

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So if you summarize how lambda works with the asynchronously, basically Lambda manage the function

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asynchronous event queue and attempts to retry on the errors.

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If the function returns an error, Lambda attempts to run it two more times with the one minute wait

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between the first two attempts and 2 minutes between the second and third attempts.

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Function errors include the error returned by the function code and the error returned by the function

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runtime such as the timeout.

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So that means lambda is a internal retry mechanism.

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If there is an exception in the lambda function code, it is retried two times and after that it return

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back to asynchronous error to the client application.