Handling S3 Bucket Trigger Event in Lambda Using Python

Question

The AWS Lambda handler has a signature of

def lambda_handler(event, context):

However, I cannot find any documentation as to the event's structure when the trigger is an S3 Bucket receiving a put

I thought that it might be defined in the s3 console, but couldn't find that there.

Anyone have any leads?

S3 event notification structure docs.aws.amazon.com/AmazonS3/latest/dev/… and configuring notifications docs.aws.amazon.com/AmazonS3/latest/dev/NotificationHowTo.html — kosa
– kosa, Commented Jun 1, 2017 at 21:26

Chan Dru · Accepted Answer · 2017-06-05 06:56:07Z

The event from S3 to Lambda function will be in json format as shown below,

{  
   "Records":[  
      {  
         "eventVersion":"2.0",
         "eventSource":"aws:s3",
         "awsRegion":"us-east-1",
         "eventTime":The time, in ISO-8601 format, for example, 1970-01-01T00:00:00.000Z, when S3 finished processing the request,
         "eventName":"event-type",
         "userIdentity":{  
            "principalId":"Amazon-customer-ID-of-the-user-who-caused-the-event"
         },
         "requestParameters":{  
            "sourceIPAddress":"ip-address-where-request-came-from"
         },
         "responseElements":{  
            "x-amz-request-id":"Amazon S3 generated request ID",
            "x-amz-id-2":"Amazon S3 host that processed the request"
         },
         "s3":{  
            "s3SchemaVersion":"1.0",
            "configurationId":"ID found in the bucket notification configuration",
            "bucket":{  
               "name":"bucket-name",
               "ownerIdentity":{  
                  "principalId":"Amazon-customer-ID-of-the-bucket-owner"
               },
               "arn":"bucket-ARN"
            },
            "object":{  
               "key":"object-key",
               "size":object-size,
               "eTag":"object eTag",
               "versionId":"object version if bucket is versioning-enabled, otherwise null",
               "sequencer": "a string representation of a hexadecimal value used to determine event sequence, 
                   only used with PUTs and DELETEs"            
            }
         }
      },
      {
          // Additional events
      }
   ]
}

here is the link for aws documentation which can guide you. http://docs.aws.amazon.com/lambda/latest/dg/with-s3-example.html

Just want to correct the URL. It should be : docs.aws.amazon.com/AmazonS3/latest/dev/…

Geoff · Accepted Answer · 2017-06-01 22:38:02Z

2

I think your easiest route is just to experiment quickly:

Create a bucket using the console
Create a lambda that is triggered by puts to the bucket using the console
Ensure you choose the default execution role, so you create cloudwatch logs
The lambda function just needs to "print(event)" when called, which is then logged
Save an object to the bucket

You'll then see the event structure in the log - its pretty self explanatory.

answered Jun 1, 2017 at 22:38

Geoff

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Comments

PhungLe · Accepted Answer · 2017-11-07 09:56:28Z

-1

Please refer this URL to get Event Message Structure: http://docs.aws.amazon.com/AmazonS3/latest/dev/notification-content-structure.html

answered Nov 7, 2017 at 9:56

PhungLe

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2 Comments

Filnor Over a year ago

This is a borderline link-only answer. You should expand your answer to include as much information here, and use the link only for reference.

PhungLe Over a year ago

Ah sorry. This question had been answered by Chan Dru above. I just want to correct the URL which links to AWS document. I also commented under the answer.

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