Lambda execution failed with status 200 due to customer function error

user_12188033 0
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I'm creating a simple Lambda function to serve a POST in AWS Gateway:

import json
import boto3
from datetime import datetime


def lambda_handler(event,context):
    wf = event['WF']
    
    if wf == 'start1':
            body = 'Suceeded'
            return {
                "isBase64Encoded": False,
                'statusCode': 200,
                'body': json.dumps(body),
                'headers': {
                'Content-Type': 'application/json'
                    }   
                }
    else:
            body = 'Failed'
            return {
                "isBase64Encoded": False,
                'statusCode': 400,
                'body': json.dumps(body),
                'headers': {
                'Content-Type': 'application/json'
                    }   
             }

If I send a POST with this body is successful:

{
  "WF": "start1",
  "Context": "OK"
}

Returns:

Test Event Name
test

Response
{
  "isBase64Encoded": false,
  "statusCode": 200,
  "body": "\"Suceeded\"",
  "headers": {
    "Content-Type": "application/json"
  }
}

Function Logs
START RequestId: 91663a9d-d8b6-4aad-b8b6-eb2f15ff0354 Version: $LATEST
END RequestId: 91663a9d-d8b6-4aad-b8b6-eb2f15ff0354
REPORT RequestId: 91663a9d-d8b6-4aad-b8b6-eb2f15ff0354  Duration: 1.74 ms   Billed Duration: 2 ms   Memory Size: 128 MB Max Memory Used: 66 MB  Init Duration: 300.73 ms

Request ID
91663a9d-d8b6-4aad-b8b6-eb2f15ff0354

But if I run a test in the API Gateway service in AWS I get:

Fri Jun 04 13:45:22 UTC 2021 : Sending request to https://XXXXXXX
Fri Jun 04 13:45:22 UTC 2021 : Received response. Status: 200, Integration latency: 15 ms
Fri Jun 04 13:45:22 UTC 2021 : Endpoint response headers: {Date=Fri, 04 Jun 2021 13:45:22 GMT, Content-Type=application/json, Content-Length=159, Connection=keep-alive, x-amzn-RequestId=d479fdac-6737-42fa-96a3-9e991056b48d, X-Amz-Function-Error=Unhandled, x-amzn-Remapped-Content-Length=0, X-Amz-Executed-Version=$LATEST, X-Amzn-Trace-Id=root=1-60ba2e72-ff62f051febbd21d6cc9d114;sampled=0}
Fri Jun 04 13:45:22 UTC 2021 : Endpoint response body before transformations: {"errorMessage": "'WF'", "errorType": "KeyError", "stackTrace": ["  File \"/var/task/lambda_function.py\", line 7, in lambda_handler\n    wf = event['WF']\n"]}
Fri Jun 04 13:45:22 UTC 2021 : Lambda execution failed with status 200 due to customer function error: 'WF'. Lambda request id: d479fdac-6737-42fa-96a3-9e991056b48d
Fri Jun 04 13:45:22 UTC 2021 : Method completed with status: 502

Why line 7 is wrong? Is there another way to parse the body of the POST?

amazon-web-services python-3.x rest api
2 Answers

It looks like your API Gateway invocation is not populating the event parameter of your Lambda function. When you create a test event your lambda function's page, you get to create your own test event. API Gateway will not use this test event, it will instead send an empty event (probably null).

I.e.


import json
import boto3
from datetime import datetime


def lambda_handler(event,context): # Event is null here
    wf = event['WF'] # Attempting to read the attribute 'WF' of null results in an error
user_42788700

The solution was found by disabling Lambda Proxy Integration in the POST - Integration Request.

user_121880330
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