Add a new item to a Dynamodb using a AWS lambda function each time a function is executed with Cloudwatch - amazon-web-services

Question

I'm trying to modify a Dynamodb table each time a Lambda function is executed.
Specifically, I create a simple lambda function that returns a list of S3 bucket names and this function run each minute thanks to a Cloudwatch's rule.
However, as I said before, my goal is to also update a Dynamodb each time the same function is executed. Specifically I want to add each time a new Item with the same attribute (so let's say the function is executed 1000 times, I want 1K items/rows).
However I don't know how to do it. Any suggestions? Here's the code:
import json
import boto3
s3 = boto3.resource('s3')
dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('Table')
def lambda_handler(event, context):
bucket_list = []
for b in s3.buckets.all():
print(b.name)
bucket_list.append(b.name)
response = "done"
table.put_item(
Item = {
"Update": response
}
)
return {
"statusCode": 200,
"body": bucket_list
}
Thank you in advance

Answer 1

Your problem is that PutItem does overwrite exiting items, if they are the same. So every time you try to insert Update=done, it just overwrites the same item.
The very first sentence of the documentation states:
Creates a new item, or replaces an old item with a new item.
So what you need to do is to put something in your item that is unique, so that a new item is created instead of the old one being overwritten.
You could create a UUID or something like that, but I think it would be beneficial to use the time of execution. This way you could see when your last execution was etc.
from datetime import datetime
[...]
table.put_item(
Item = {
"Update": response,
"ProcessingTime": datetime.now().isoformat()
}
)

Answer 2

Adding to what Jens stated, which is 100% correct.
You could use data from the event. The event will look something like this:
{
"id": "cdc73f9d-aea9-11e3-9d5a-835b769c0d9c",
"detail-type": "Scheduled Event",
"source": "aws.events",
"account": "123456789012",
"time": "1970-01-01T00:00:00Z",
"region": "us-west-2",
"resources": [
"arn:aws:events:us-west-2:123456789012:rule/ExampleRule"
],
"detail": {}
}
The id value will be 100% unique, and the time value will be the time it was triggered.