Lambda Functions UnsupportedMediaTypeException

What is Lambda Functions UnsupportedMediaTypeException

Understanding AWS Lambda

AWS Lambda is a serverless compute service that allows you to run code without provisioning or managing servers. It automatically scales your applications by running code in response to triggers such as changes in data, shifts in system state, or user actions. Lambda supports a variety of programming languages, making it a versatile tool for developers.

Identifying the Symptom: UnsupportedMediaTypeException

When working with AWS Lambda, you might encounter the UnsupportedMediaTypeException. This error typically occurs when the content type of a request is not supported by the Lambda function. It is a common issue when integrating Lambda with other AWS services or external APIs.

What You Observe

When this exception is thrown, you will notice that your Lambda function fails to execute as expected. The error message will indicate that the media type of the request is not supported, which can be confusing if you are not familiar with content types.

Exploring the Issue: UnsupportedMediaTypeException

The UnsupportedMediaTypeException is an HTTP error that indicates the server refuses to accept the request because the payload format is in an unsupported format. In the context of AWS Lambda, this often means that the Content-Type header of the request does not match what the Lambda function expects.

Common Causes

Incorrect Content-Type header in the request. Lambda function not configured to handle the specified content type. Misconfigured API Gateway or other services interfacing with Lambda.

Steps to Resolve UnsupportedMediaTypeException

To resolve this issue, you need to ensure that the request content type is supported and correctly specified. Follow these steps:

Step 1: Verify the Content-Type Header

Check the Content-Type header in your request. Ensure it matches the expected format. Common content types include application/json, text/plain, and application/xml. For example, if your Lambda function expects JSON, the header should be:

Content-Type: application/json

Step 2: Update Lambda Function Configuration

Ensure your Lambda function is configured to handle the specified content type. If your function processes JSON, make sure your code parses the JSON input correctly. You can refer to the AWS Lambda Developer Guide for more information on configuring Lambda functions.

Step 3: Check API Gateway Settings

If your Lambda function is triggered via API Gateway, verify that the API Gateway is configured to accept the content type. You can do this by checking the API Gateway documentation for guidance on setting up content types.

Step 4: Test and Validate

After making the necessary changes, test your Lambda function to ensure it processes requests correctly. Use tools like Postman or cURL to send requests with the correct content type and verify the response.

Conclusion

By ensuring that the Content-Type header is correctly specified and that your Lambda function is configured to handle the expected content type, you can resolve the UnsupportedMediaTypeException. Proper configuration and testing are key to seamless Lambda function execution.