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Lambda Asynchronous Invocation

Links: 102 AWS DVA Index

Asynchronous Invocations

The main difference between asynchronous and synchronous invocations is that in asynchronous invocations we don't get the results we just get a status code of 202.

Same status code of 202 is returned when the function is invoked asynchronously regardless if the function fails or succeeds.

  • They are for services which invoke lambda function because of an event.
    • S3
    • Simple Notification Service (SNS)
    • Cloud Watch Events/EventBridge
    • There are more services which make use of asynchronous processing but it is not important for exam.
We can invoke Lambda at regular intervals using CloudWatch Events. Completely serverless.
The above services can invoke the lambda because of lambda's resource based policy.

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This says S3 can invoke our function

  • The events are placed in an Event Queue
  • Lambda attempts to retry on errors
    • Max 3 tries
    • Minute wait after 1st and then 2 minutes wait
  • Make sure the processing is idempotent. That is in case of retries the result should be the same.
  • If the function is retried, you will see duplicate logs entries in CloudWatch Logs
  • Can define a DLQ (dead-letter queue) SNS or SQS for failed processing (need correct IAM permissions). Or we can use Lambda Destinations.
    • We will need to modify the execution role of the lambda and include SQS permission.
    • attachments/Pasted image 20220523163231.jpg
An application uses AWS Lambda to process many files. The Lambda function takes approximately 3 minutes to process each file and does not return any important data. A Developer has written a script that will invoke the function using the AWS CLI. What is the FASTEST way to process all the files?

Invoke the Lambda function asynchronously with the invocation type Event and process the files in parallel.

RequestResponse is used for synchronous invocations

CloudWatch with Lambda

  • Two ways
    • Serverless cron/rate
      • A resource based policy is created so that CloudWatch can invoke lambda.
    • CodePipeline EventBride rule to invoke a lambda on state changes

Last updated: 2023-02-15