Aws lambda code explanation - aws-lambda

Question

Can anybody please explain the working of the below code.
"def lambda_handlerOut(event, context):
if len(event) > 0:
success=1
print("length of event outside for--"+str(len(event)))
for record in event['Records']:
print("length of event--"+str(len(event)))
bucket=record['s3']['bucket']['name']
key=record['s3']['object']['key']
print("Bucket--"+bucket)
print("File that triggered this event--"+key)
Thanks in advance.
Regards,
Eleena Jose

Answer 1

This is a Lambda that receives S3 events - for example a PutObject request that creates a new file.
The method is the standard Python function - take a look at the Lambda Function Handler Docs for more details.
The structure of the event is defined here but basically there are some number of Records that are being iterated through with and, for each record, the bucket and key are being extracted and printed.
So, in more detail (comments above the line they reference):
# standard lambda event handler definition
def lambda_handlerOut(event, context):
# make sure that something was given - likely unneeded
if len(event) > 0:
success=1
print("length of event outside for--"+str(len(event)))
# loop through each record in Records
for record in event['Records']:
print("length of event--"+str(len(event)))
# take a look at the event structure - just extracting parts
bucket=record['s3']['bucket']['name']
# key is the object name - that is, the file
key=record['s3']['object']['key']
print("Bucket--"+bucket)
print("File that triggered this event--"+key)
EDIT
As I linked to above, the data in the event object looks something like:
{
"Records":[
{
"eventVersion":"2.0",
"eventSource":"aws:s3",
"awsRegion":"us-east-1",
"eventTime":"1970-01-01T00:00:00.000Z",
"eventName":"ObjectCreated:Put",
"userIdentity":{
"principalId":"AIDAJDPLRKLG7UEXAMPLE"
},
"requestParameters":{
"sourceIPAddress":"127.0.0.1"
},
"responseElements":{
"x-amz-request-id":"C3D13FE58DE4C810",
"x-amz-id-2":"FMyUVURIY8/IgAtTv8xRjskZQpcIZ9KG4V5Wp6S7S/JRWeUWerMUE5JgHvANOjpD"
},
"s3":{
"s3SchemaVersion":"1.0",
"configurationId":"testConfigRule",
"bucket":{
"name":"mybucket",
"ownerIdentity":{
"principalId":"A3NL1KOZZKExample"
},
"arn":"arn:aws:s3:::mybucket"
},
"object":{
"key":"HappyFace.jpg",
"size":1024,
"eTag":"d41d8cd98f00b204e9800998ecf8427e",
"versionId":"096fKKXTRTtl3on89fVO.nfljtsv6qko",
"sequencer":"0055AED6DCD90281E5"
}
}
}
]
}
So, as an example, bucket=record['s3']['bucket']['name'] starts by getting the s3 record from the data which leaves:
"s3":{
"s3SchemaVersion":"1.0",
"configurationId":"testConfigRule",
"bucket":{
"name":"mybucket",
"ownerIdentity":{
"principalId":"A3NL1KOZZKExample"
},
"arn":"arn:aws:s3:::mybucket"
},
"object":{
"key":"HappyFace.jpg",
"size":1024,
"eTag":"d41d8cd98f00b204e9800998ecf8427e",
"versionId":"096fKKXTRTtl3on89fVO.nfljtsv6qko",
"sequencer":"0055AED6DCD90281E5"
}
}
From there, it gets the bucket stanza:
"bucket":{
"name":"mybucket",
"ownerIdentity":{
"principalId":"A3NL1KOZZKExample"
},
"arn":"arn:aws:s3:::mybucket"
}
and lastly, the name:
"name":"mybucket"
This is assigned to the variable bucket which is printed out later. The key (which is the file name in this example) works the same way but gets different parts of the event.
Does that make sense now?