"KeyError: 'Records'" in AWS S3 - Lambda trigger

I had this issue yesterday and the problem is when you run a test there isn't actually any event (def lambda_handler(event, context)) for lambda to process. The event document is normally generated when an actual event occurs which is a json doc, your python code parses this document and then retrieves the keys. So the solution is for you to create an actual event by dropping a file in s3 so long as you have created event notification then this would get picked up

bit late to the party. But here is my first post!

EXPLANATION:

When you test in lambda panel -> def lambda_handler(event, context) <- event is injected directly.

However in AWS API its neccessary to add Mapping Template or otherwise -> event <- is empty, thus resulting in quizzing:

"errorType": "KeyError", "errorMessage": "'Records'"

this is null pointer. Records doesnt exist, since -> event <- doesnt exist.

SOLUTION:

You need to configure Integration Request inside AWS API. Click on Body Mapping Templates. Then add Mapping Template Set content type to application/json Then edit generated mapping template:

{
  "body" : $input.json('$'),
  "headers": {
    #foreach($header in $input.params().header.keySet())
    "$header": "$util.escapeJavaScript($input.params().header.get($header))" #if($foreach.hasNext),#end

    #end
  },
  "method": "$context.httpMethod",
  "params": {
    #foreach($param in $input.params().path.keySet())
    "$param": "$util.escapeJavaScript($input.params().path.get($param))" #if($foreach.hasNext),#end

    #end
  },
  "query": {
    #foreach($queryParam in $input.params().querystring.keySet())
    "$queryParam": "$util.escapeJavaScript($input.params().querystring.get($queryParam))" #if($foreach.hasNext),#end

    #end
  }  
}

And edit Lambda function:

replace:

for record in event['Records']:

with:

for record in event['query']['Records']

don't know whether stack will ping you with this answer - so i call you @Dawny33 @KevinOelen @franklinsijo

As for explanation i figured it on my own. However "mapping template" comes from https://medium.com/simple-thoughts-amplified/passing-variables-from-aws-api-gateway-to-lambda-3c5d8602081b