Invoking lambda from lambda: AWS Lambda concurrent execution limits

Question

My current AWS Lambda function invokes another AWS Lambda function but I want to make sure that the invoke succeeded. After looking at concurrent execution limits for AWS Lambda I am trying to figure out what would happen if the concurrent limit is hit and I tried to invoke the Lambda from another Lambda. For now, I am solving this problem by putting messages in an SNS but I rather prefer invoking Lambda directly avoiding the indirection.

Answer 1

The best way to handle the concurrent limit is to use a Kinesis stream rather than SNS. The number of shards will limit the number of lambda invoked. And if it pertinent for you, you can take several messages at once, which you can't do with SNS, and that can lead to hit the concurrent limit.

Answer 2

Can you elaborate a little? Not sure I Understand what you are trying to achieve.

Lambda limits can be viewed under AWS console / EC2 page, top left corner has menu item called Limits, there you should see the limit. When you hit the limit, lambda will stop being Invoked, and if my memory serves me right you will see an error in the logs saying something about limit being hit.

Answer 3

From the AWS Lambda FAQs :

Q: What happens if my account exceeds the default throttle limit on concurrent executions?

On exceeding the throttle limit, AWS Lambda functions being invoked synchronously will return a throttling error (429 error code). Lambda functions being invoked asynchronously can absorb reasonable bursts of traffic for approximately 15-30 minutes, after which incoming events will be rejected as throttled. In case the Lambda function is being invoked in response to Amazon S3 events, events rejected by AWS Lambda may be retained and retried by S3 for 24 hours. Events from Amazon Kinesis streams and Amazon DynamoDB streams are retried until the Lambda function succeeds or the data expires. Amazon Kinesis and Amazon DynamoDB Streams retain data for 24 hours.

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Inside the AWS Console you can always create a Service Limit Increase for AWS Lambda concurrent executions at no additional cost. This answer explains this in more detail.

Answer 4

I believe you're handling it correctly currently. I was just reading an article that was explaining how you shouldn't invoke lambda from another lambda because:

"If you do, the first will run until the second is finished executing, and you're double billing yourself. Instead, use SNS or SQS to send a message to the other Lambda."

http://web.archive.org/web/20160713113906/http://www.appliedsoftwaredesign.com/archives/aws-lambda-pro-tips/