# Excessive Lambda Retries (Retry Storms)

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# Excessive Lambda Retries (Retry Storms)

## Explanation

Retry storms occur when a function fails and is automatically retried repeatedly due to default retry behavior for asynchronous events (e.g., SQS, EventBridge). If the error is persistent and unhandled, retries can accumulate rapidly - often invisibly - creating a large volume of billable executions with no successful outcome. This is especially costly when functions run for extended durations or have high memory allocation.

## Relevant Billing Model

\* Each retry counts as a separate request \* Billed per millisecond of execution time for each retry \* Retries from failed invocations can exponentially increase cost if not controlled

## Detection

- Check for high error-to-success ratios in CloudWatch Metrics

- Investigate spikes in invocation count after initial failure events

- Correlate retries with common payloads and error messages

- Review configurations for MaximumRetryAttempts and DLQs

- Assess the presence of throttling, downstream timeouts, or missing exception handling

## Remediation

- Configure DLQs to isolate and inspect failed invocations

- Implement exponential backoff or circuit breaker patterns in retry logic

- Set appropriate retry limits on event source mappings

- Improve exception handling and idempotency in function code

- Utilize anomaly detection software to alert on abnormal retry patterns

- Monitor CloudWatch for retry-specific metrics and alarms

## Relevant Documentation

[https://docs.aws.amazon.com/lambda/latest/dg/invocation-retries.html](https://docs.aws.amazon.com/lambda/latest/dg/invocation-retries.html) 
[https://docs.aws.amazon.com/lambda/latest/dg/invocation-async.html\\#invocation-dlq](https://docs.aws.amazon.com/lambda/latest/dg/invocation-async.html#invocation-dlq) 
[https://docs.aws.amazon.com/lambda/latest/dg/invocation-eventsourcemapping.html\\#invocation-eventsourcemapping-retries](https://docs.aws.amazon.com/lambda/latest/dg/invocation-eventsourcemapping.html#invocation-eventsourcemapping-retries) 
[https://aws.amazon.com/lambda/pricing/](https://aws.amazon.com/lambda/pricing/)

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## At a glance

Reference

CER-0213

Cloud provider

AWS

Service

AWS Lambda

Category

[Compute](https://www.pointfive.co/efficiency-hub/service-category/compute)

Inefficiency type

Retry Misconfiguration

## Contributed by

- Liam Greenamyre 

### Liam Greenamyre

Principal Product Manager (Technical - External Services) @ Amazon Web Services (AWS)

[LinkedIn](https://www.linkedin.com/in/liam-greenamyre-01606310/)

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