Handling Lambda errors with an API Gateway API - AWS Lambda

Handling Lambda errors with an API Gateway API

API Gateway treats all invocation and function errors as internal errors. If the Lambda API rejects the invocation request, API Gateway returns a 500 error code. If the function runs but returns an error, or returns a response in the wrong format, API Gateway returns a 502. In both cases, the body of the response from API Gateway is {"message": "Internal server error"}.

Note

API Gateway does not retry any Lambda invocations. If Lambda returns an error, API Gateway returns an error response to the client.

The following example shows an X-Ray trace map for a request that resulted in a function error and a 502 from API Gateway. The client receives the generic error message.

Trace map for a function error with API Gateway.

To customize the error response, you must catch errors in your code and format a response in the required format.

Example index.mjs – Error formatting
var formatError = function(error){ var response = { "statusCode": error.statusCode, "headers": { "Content-Type": "text/plain", "x-amzn-ErrorType": error.code }, "isBase64Encoded": false, "body": error.code + ": " + error.message } return response }

API Gateway converts this response into an HTTP error with a custom status code and body. In the trace map, the function node is green because it handled the error.

Trace map for a formatted error with API Gateway.