“KeyError: 'Records'” in AWS S3 - Lambda trigger

Question

I have the following lambda function code for simply printing out the Author and metadata of an uploaded event of an S3 bucket: 

from __future__ import print_function

import json

import urllib

import boto3

 

print('Loading function')

 

s3 = boto3.client('s3')

 

 

def lambda_handler(event, context):

 

    #print("Received event: " + json.dumps(event, indent=2))

    # bucket = event['Records'][0]['s3']['bucket']['name']

 

    for record in event['Records']:

        bucket = record[0]['s3']['bucket']['name']

        key = record[0]['s3']['object']['key']

        response = s3.head_object(Bucket=bucket, Key=key)

 

        logger.info('Response: {}'.format(response))

 

        print("Author : " + response['Metadata']['author'])

        print("Description : " + response['Metadata']['description'])

However, I am getting the following error while testing:

{

  "stackTrace": [

    [

      "/var/task/lambda_function.py",

      17,

      "lambda_handler",

      "for record in event['Records']:"

    ]

  ],

  "errorType": "KeyError",

  "errorMessage": "'Records'"

}

Am I doing anything wrong while accessing the bucket name and key name of the S3 object? If not, then what am I doing wrong here? 

Answer 1

Inside the AWS API, we have to configure the Integration Request. This can be done by clicking on Body Mapping Templates, Then set the content type to application/json. A generated mapping template appears, and edit it like this:

{

  "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

  }  

}

Also, edit this part in the lambda function.

replace:

for record in event['Records']:

with:

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

Answer 2

This error message `KeyError: 'Records'` is because your event object doesn't have an entry for `'Records'`. This usually occurs when you're testing the Lambda function with a wrong structure of an event.

Solutions

1. Find 'Records': Add a check to see if `'Records'` is present in your event:

return

)

"key": "your-object-key"

}

}

}

]

This should clear the error and let you access the details of your S3 object properly.