Why do I get a KeyError when testing an S3 triggered Lambda that invalidates files in CloudFront?

Question

I have a Python 3.7 Lambda function that invalidates CloudFront cache:

from __future__ import print_function

import boto3
import time

def lambda_handler(event, context):
    print(event)
    for items in event["Records"]:
        path = "/" + items["s3"]["object"]["key"]
    print(path)
    client = boto3.client('cloudfront')
    invalidation = client.create_invalidation(DistributionId='distributionid__ID',
        InvalidationBatch={
            'Paths': {
                'Quantity': 1,
                'Items': [path]
        },
        'CallerReference': str(time.time())
    })

This is the attached IAM policy:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "logs:CreateLogGroup",
                "logs:CreateLogStream",
                "logs:PutLogEvents"
            ],
            "Resource": "arn:aws:logs:*:*:*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "cloudfront:CreateInvalidation"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}

This is my test JSON:

{
  "key1": "*"
}

Whenever I invoke my Lambda function, I get this error:

{'key 1': '*'}
[ERROR] KeyError: 'Records'
Traceback (most recent call last):
Version: $LATEST
    File "/var/task/lambda_function.py", line 8, in lambda_handler
        for items in event["Records"]:

Asked By: Santosh

||

Source

Answer 1

The issue here is your input JSON – the code is expecting an Amazon S3 Event Notification.

Your input JSON does not have the correct structure as per docs, for an event message.

The Lambda errors as for items in event["Records"]: requires a Records property which is an array. You don’t have this property at all in your JSON, resulting in the KeyError in the logs.

The below barebones test event should work, keeping in mind that you would never get * in real S3 event notifications.

{"Records":[{"s3":{"object":{"key":"*"}}}]}

Answered By: Ermiya Eskandary

Why do I get a KeyError when testing an S3 triggered Lambda that invalidates files in CloudFront?

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