Fix AWS Lambda Error 429 Too Many Requests Throttling (2025)

Updated: 11/29/2025

Your AWS Lambda function works fine in testing, but under real traffic you start seeing 429 Too Many Requests errors, throttling metrics spike, and some users experience slow or failed responses. This code means Lambda or a downstream AWS service is receiving more requests than its configured limits, and it is deliberately rejecting or delaying new invocations to protect stability.

Table of Contents

Method 1: Understand And Adjust Lambda Concurrency Limits

If your overall Lambda usage regularly pushes against the regional account limit, open a support case with AWS to request an increase. Provide metrics and a brief description of your workload so AWS can evaluate and raise the concurrency ceiling appropriately.

Method 2: Implement Backoff, Queues, And Smoother Traffic Patterns

For functions that must respond quickly under heavy load, enable Provisioned Concurrency so a specified number of Lambda instances are always warm and ready. This reduces cold start impact and can help handle peaks more smoothly, lowering the chance of throttling.

Warning: Provisioned Concurrency and higher concurrency limits increase cost, so size them carefully based on realistic traffic patterns and monitoring data.

Method 3: Tune Downstream Service Limits And Per Resource Usage

Optimize your Lambda code to do less per call, such as batching writes to DynamoDB, caching configuration or secrets, and avoiding unnecessary external calls. Smaller, more efficient operations lower the pressure on all components and reduce the risk of hitting per second rate limits that cause 429s.