AWS Serverless: Understanding and Managing Lambda Recursive Loops for Event-Driven Architectures

In this article, I will explain an important feature of AWS Lambda: Lambda Recursive Loop Configuration.

Before July 2023, the only way to avoid recursive loops was by carefully designing an event-driven architecture and thoroughly testing your applications to ensure that bugs didn’t unintentionally cause recursive loops. These loops could lead to increased costs, degraded performance, and excessive resource consumption.

In July 2023, AWS introduced Lambda Recursive Loop Configuration, providing a built-in mechanism to mitigate the risks of recursive loops.

Let’s review what a Lambda recursive loop is and explore an example of an event-driven architecture that can trigger this scenario.

Let's look at the architecture diagram!

What is Lambda Recursive Loop?

A Lambda recursive loop refers to a scenario where a Lambda function is invoked recursively, creating a kind of infinite loop. It's similar to a do-while loop without an exit condition.
In an event-driven architecture, this situation can arise when services like SQS and Lambda unintentionally invoke each other in a loop.

For example, consider the following scenario:

• A message is published to an SQS queue.
• The SQS queue is configured with an event trigger to invoke a Lambda function for processing.
• The Lambda function then publishes the message back to the same SQS queue (intentionally or due to a design flaw or code bug). This creates a loop where the message continuously cycles between the queue and the Lambda function.

If left unchecked, a recursive loop can:

• Consume your account's allocated concurrency, leading to throttling and timeouts.
• Drive up costs significantly.
• Negatively impact other critical application functions by monopolizing available resources.

When Was Support Announced?

AWS announced support for Lambda recursive loop configuration in July 2023. This feature enables you to detect and prevent recursive loops in your Lambda functions. By default, this configuration is enabled for all accounts, ensuring Lambda functions automatically detect and stop infinite loops.

Supported Services (as of January 2025)

The following services are supported by the Lambda recursive loop configuration feature:

• Amazon Simple Queue Service (SQS)
• Amazon Simple Notification Service (SNS)
• Amazon Simple Storage Service (S3)

Key Points to Consider

Configuration Default

The Lambda recursive loop configuration is enabled by default.
If your business use case requires disabling this feature, ensure you have alternative guardrails in place, such as:

• Budget monitoring
• Function invocation monitoring
• CloudWatch alarms

Detection and Handling

With this feature, Lambda detects recursive loops from the same event and stops invocation after it exceeds 16 attempts.

Notifications and Metrics

When a recursive loop is detected, AWS sends a notification to your Account Health Dashboard under the "Other Notifications" tab.

An email is also sent to inform you of the detection. This email:

• Is sent once in 24 hours.
• May take up to 3 hours to arrive.

The CloudWatch metric RecursiveInvocationsDropped records the number of dropped recursive invocations, enabling you to monitor and analyze these occurrences.

Create a SQS Queue

First, let’s create an SQS queue. This will be a standard queue, and I will name it contactQueue. Contact information, including phone numbers and names in JSON format, will be published to this queue. Once a message is published, it will trigger a Lambda function for further processing.

The use case for the Lambda function is to publish the contact information to another queue for final processing. However, in this scenario, I will intentionally publish the message back to the contactQueue to simulate a recursive loop.

Create Lambda Function

I am creating the Lambda function using the AWS Management Console, although the same can be achieved using an Infrastructure as Code (IaC) approach with AWS SAM.

The function will be named contactExample, and I will select Python 3.13 as the runtime.

The function's code will process messages from the contactQueue, extract data elements such as phone numbers and names from the message payload, and perform further processing. As part of this process, the function will publish the message back to the contactQueue, simulating a recursive loop.

Create Event Mapping between Lambda and SQS

Now that both the queue and the Lambda function are set up, I will create an event mapping. This configuration ensures that the Lambda function is triggered whenever a contact is published to the contactQueue.

Please ensure the following:

• The Lambda function has the necessary permissions to publish messages to the contactQueue.
• The Lambda function has recursive loop termination enabled. This configuration is enabled by default, but it’s a good practice to verify it by reviewing the Lambda function’s recursive loop detection settings.

Trigger the Event by publishing a msg to SQS Queue

The queue and lambda function configuration is now compete. To validate this, I will publish a message to the contactQueue.

This will trigger invocation of lambda. Lambda publishes back to SQS, hence it becomes recursive loop.

Monitor and Notifications

Once a recursive loop is detected, you will be notified through the AWS Health Dashboard and via email.

**Health Dashboard Notification: **The notification can be reviewed under the "Other Notifications" tab. An example is provided below.

Email Notification: An email will be sent to the account owner, notifying them that a recursive loop has been detected. An example of this email is shown below.

In addition to these default notifications, you can set up custom monitoring by observing the Lambda function invocations, specifically the RecursiveInvocationsDropped metric.

Cleanup - Delete the Lambda function & SQS Queue

Once you are done with this exercise, ensure you delete the Lambda function to avoid unnecessary resource usage. Additionally, delete the SQS Queue. If you created any new roles during the process, remember to delete that as well.

Conclusion

In this article, I demonstrated how to validate a Lambda Recursive Loop Configuration. I used a SQS Queue and Lambda function event mapping to create a recursive invocation scenario. The entire configuration and validation steps, including the creation and setup of the SQS queue and Lambda function, were done using the AWS Management Console.

I hope you found this article both helpful and informative!

Thank you for reading!

Watch the video here:

https://www.youtube.com/watch?v=f0TiH4zdCt4

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