DEV Community

Cover image for How to Trigger an AWS Lambda from DynamoDB
AWS Community Builders profile image Alex Kates
Alex Kates for AWS Community Builders

Posted on • Edited on • Originally published at alexkates.dev

How to Trigger an AWS Lambda from DynamoDB

#aws #cloud #devops #eventdriven

In this post we are going to use the AWS CDK to build an AWS Lambda Function that triggers from DynamoDB Stream Events.

All of the code can be found in this repository.

Setup

We need to run a few commands to setup our CDK app.

mkdir how-to-trigger-lambda-from-ddb-stream
cd how-to-trigger-lambda-from-ddb-stream
npx cdk init app --language typescript
Enter fullscreen mode Exit fullscreen mode

This should give you the following directory structure.

Alt Text

Also make sure you have your AWS CLI configured. For more information follow the AWS CLI quickstart guide.

DynamoDB

Install the DynamoDB CDK package.

npm i @aws-cdk/aws-dynamodb
Enter fullscreen mode Exit fullscreen mode

Open lib/how-to-trigger-lambda-from-ddb-stream-stack.ts, add a new DynamoDB table and deploy.

import * as cdk from '@aws-cdk/core';
import * as dynamodb from '@aws-cdk/aws-dynamodb';

export class HowToTriggerLambdaFromDdbStreamStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const table = new dynamodb.Table(this, 'Table', {
      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
      partitionKey: { name: 'id', type: dynamodb.AttributeType.STRING },
      stream: dynamodb.StreamViewType.NEW_AND_OLD_IMAGES,
      tableName: 'Table',
    });
  }
}
Enter fullscreen mode Exit fullscreen mode 
npm run cdk deploy
Enter fullscreen mode Exit fullscreen mode

Lambda

Install the Lambda CDK package.

npm i @aws-cdk/aws-lambda
Enter fullscreen mode Exit fullscreen mode

Deploying Lambda functions requires bootstrapping your CDK app which gives us an S3 bucket where our Lambda's source code will live.

npm run cdk bootstrap
Enter fullscreen mode Exit fullscreen mode

Create src/index.js and paste the following code

exports.handler = async (event) => {
    event.Records.forEach((record) => {
        console.log('Event Id: %s', record.eventID);
        console.log('Event Id: %s', record.eventName);
        console.log('DynamoDB Record: %j', record.dynamodb);
    });
};
Enter fullscreen mode Exit fullscreen mode

Open lib/how-to-trigger-lambda-from-ddb-stream-stack.ts, add a new Lambda function and deploy.

import * as cdk from '@aws-cdk/core';
import * as dynamodb from '@aws-cdk/aws-dynamodb';
import * as lambda from '@aws-cdk/aws-lambda';

export class HowToTriggerLambdaFromDdbStreamStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const table = new dynamodb.Table(this, 'Table', {
      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
      partitionKey: { name: 'id', type: dynamodb.AttributeType.STRING },
      tableName: 'Table',
    });

    const lambdaFunction = new lambda.Function(this, 'Function', {
      code: lambda.Code.fromAsset('src'),
      handler: 'index.handler',
      functionName: 'TableStreamHandler',
      runtime: lambda.Runtime.NODEJS_12_X,
    });
  }
}
Enter fullscreen mode Exit fullscreen mode 
npm run cdk deploy
Enter fullscreen mode Exit fullscreen mode

Event Source

Install the Lambda Event Sources CDK package.

npm i @aws-cdk/aws-lambda-event-sources
Enter fullscreen mode Exit fullscreen mode

Open lib/how-to-trigger-lambda-from-ddb-stream-stack.ts, add a new DynamoEventSource to the Lambda Function.

import * as cdk from '@aws-cdk/core';
import * as dynamodb from '@aws-cdk/aws-dynamodb';
import * as lambda from '@aws-cdk/aws-lambda';
import { DynamoEventSource } from '@aws-cdk/aws-lambda-event-sources';

export class HowToTriggerLambdaFromDdbStreamStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const table = new dynamodb.Table(this, 'Table', {
      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
      partitionKey: { name: 'id', type: dynamodb.AttributeType.STRING },
      stream: dynamodb.StreamViewType.NEW_AND_OLD_IMAGES,
      tableName: 'Table',
    });

    const lambdaFunction = new lambda.Function(this, 'Function', {
      code: lambda.Code.fromAsset('src'),
      handler: 'index.handler',
      functionName: 'TableStreamHandler',
      runtime: lambda.Runtime.NODEJS_12_X,
    });

    lambdaFunction.addEventSource(new DynamoEventSource(table, {
      startingPosition: lambda.StartingPosition.LATEST,
    }));
  }
}
Enter fullscreen mode Exit fullscreen mode 
npm run cdk deploy
Enter fullscreen mode Exit fullscreen mode

Testing

Using the AWS CLI, insert a new item into the DynamoDB table.

aws dynamodb put-item \
    --table-name Table \
    --item '{
        "id": {"S": "test123"}
      }'
Enter fullscreen mode Exit fullscreen mode

Verify that the Lambda executed by looking in CloudWatch. Find the LogGroup named /aws/lambda/TableStreamHandler and open up the latest LogStream. You should see some log messages that look similar to this.

2021-05-14T19:08:55.487Z    ffba16f2-846b-4c6e-9ff5-189c3293116e    INFO    Event Id: e6db4f872fd1997f0f459bcebb8163e8
Enter fullscreen mode Exit fullscreen mode 
2021-05-14T19:08:55.527Z    ffba16f2-846b-4c6e-9ff5-189c3293116e    INFO    Event Id: INSERT
Enter fullscreen mode Exit fullscreen mode 
2021-05-14T19:08:55.527Z    ffba16f2-846b-4c6e-9ff5-189c3293116e    INFO    DynamoDB Record: {
    "ApproximateCreationDateTime": 1621019335,
    "Keys": {
        "id": {
            "S": "test123"
        }
    },
    "NewImage": {
        "id": {
            "S": "test123"
        }
    },
    "SequenceNumber": "733400000000008471956488",
    "SizeBytes": 18,
    "StreamViewType": "NEW_AND_OLD_IMAGES"
}
Enter fullscreen mode Exit fullscreen mode

Summary

Congratulations. If you've made it this far then you successfully ...

  1. Scaffolded a new CDK app
  2. Created a DynamoDB table
  3. Created a Lambda Function
  4. Created a DynamoEventSource for the Lambda Function

Top comments (0)

Read next

dilip_verma_30f015f2a452f profile image

10 Shocking React and Node.js Tips That Will Change the Way You Code Forever!

Dilip Verma -

mrcaption49 profile image

PL/SQL Developer Interview Questions with 3 years of experience

Pranav Bakare -

s3cloudhub profile image

Azure Cloud Computing Platform: Unlocking Endless Possibilities 🌍

S3CloudHub -

teti_most profile image

Understanding RabbitMQ Brokers in AWS

Tetiana Mostova -