Learn how to fix the “502 Bad Gateway Lambda Function URL“ error. Our AWS Support team is here to help you with your questions and concerns.

502 Bad Gateway Lambda Function URL | Troubleshooting

If you have been having trouble with the “502 Bad Gateway error” while using AWS API Gateway, you have come to the right place.

According to our experts, this error lets us know that a server upstream, acting as a gateway or proxy, has received an invalid response from an inbound server while trying to fulfill a request.

In relation to AWS API Gateway, this indicates issues in the Lambda function or the API Gateway service itself.

What Causes a 502 Bad Gateway Error?

Several factors can lead to a 502 error:

• If the Lambda function fails to return a response in the expected format, API Gateway cannot parse it, resulting in an error.
• Connectivity problems between API Gateway and VMs or containers can cause a 502 error if they are not running correctly.
• Sometimes, issues within the API Gateway service itself can casue this error.

Common Causes Behind the Error

• When the Lambda function exceeds the configured timeout, it fails to respond in time, leading to a 502 error.
• If the Lambda function reaches its concurrency limit, it may reject additional requests, causing timeouts.
• After a period of inactivity, a Lambda function may have a cold start, resulting in delayed responses and potential timeouts.

How to Fix a 502 Bad Gateway Error on AWS

• Frist, make sure that Lambda function returns a response in the expected JSON format with “statusCode,” “headers,” and “body” properties.
• Next, review CloudWatch logs for any errors or exceptions during function execution.
• Then, adjust the API Gateway timeout settings if the Lambda function consistently exceeds the configured timeout.
• Additionally, monitor and adjust Lambda concurrency limits to prevent overload.
• if the error still occurs, use strategies like provisioned concurrency or periodic invocations to reduce cold starts.
• Also, use retry mechanisms in client applications to handle errors.

Let us know in the comments if the above troubleshooting tips did not help resolve the error.

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Conclusion

In brief, our Support Experts demonstrated how to fix the “ 502 Bad Gateway Lambda Function URL” error.