Lambda note

Quick Start With DynamoDB

A DynamoDB stream is an ordered flow of information about changes to items in an Amazon DynamoDB table. In this case, lambda function poll the stream of DynamoDB 4 times per seconds and be trigered by an event of DynamoDB stream.

Futher reading:

Capturing Table Activity with DynamoDB Streams

Process Stream of DynamoDB

First, git clone the sam example from GitHub

# clone the examples
$ git clone https://github.com/awslabs/serverless-application-model

# change dir to dynamodb-process-stream-python3
$ cd serverless-application-model/examples/apps/dynamodb-process-stream-python3

# run the sam local generate-event to generate dynamodb stream event
$ sam local generate-event dynamodb > dynamodb-event.json

# invoke the lambda function
$ sam local invoke -e dynamodb-event.json dynamodbprocessstreampython

# package the lambda function
$ sam package --template-file template.yaml --s3-bucket crazyaws-lambda --output-template-file packaged.yaml

# deploy the lambda function to aws
$ sam deploy --template-file packaged-template.yaml --stack-name dynamodb-lambda --capabilities CAPABILITY_IAM

Create an Item in Table

After run the command: sam deploy, we can find a dynamodb table on AWS. In this case, creating a item in table can trigger the lambda function which we have created previously.

Step 1: Go to DynamoDB console

Step 2: Create an Item in Table

Step 3: Go to CloudWatch console and click Logs, we can find that the lambda function has been triggered.

Sample Code

template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'
Description: An Amazon DynamoDB trigger that logs the updates made to a table.
Resources:
  dynamodbprocessstreampython3:
    Type: 'AWS::Serverless::Function'
    Properties:
      Handler: lambda_function.lambda_handler
      Runtime: python3.6
      CodeUri: .
      Description: An Amazon DynamoDB trigger that logs the updates made to a table.
      MemorySize: 128
      Timeout: 3
      Policies: []
      Events:
        DynamoDB1:
          Type: DynamoDB
          Properties:
            Stream:
              'Fn::GetAtt':
                - Table1
                - StreamArn
            StartingPosition: TRIM_HORIZON
            BatchSize: 100
  Table1:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: 5
        WriteCapacityUnits: 5
      StreamSpecification:
        StreamViewType: NEW_IMAGE

lambda_function.py

import json

print('Loading function')


def lambda_handler(event, context):
    #print("Received event: " + json.dumps(event, indent=2))
    for record in event['Records']:
        print(record['eventID'])
        print(record['eventName'])
        print("DynamoDB Record: " + json.dumps(record['dynamodb'], indent=2))
    return 'Successfully processed {} records.'.format(len(event['Records']))

event.json

{
  "Records": [
    {
      "eventID": "1",
      "eventVersion": "1.0",
      "dynamodb": {
        "Keys": {
          "Id": {
            "N": "101"
          }
        },
        "NewImage": {
          "Message": {
            "S": "New item!"
          },
          "Id": {
            "N": "101"
          }
        },
        "StreamViewType": "NEW_AND_OLD_IMAGES",
        "SequenceNumber": "111",
        "SizeBytes": 26
      },
      "awsRegion": "us-east-1",
      "eventName": "INSERT",
      "eventSourceARN": "arn:aws:dynamodb:us-east-1:account-id:table/ExampleTableWithStream/stream/2015-06-27T00:48:05.899",
      "eventSource": "aws:dynamodb"
    }
  ]
}