In this post we are going to use the AWS CDK to build an AWS Lambda Function that triggers from AWS S3 Put requests.
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-s3
cd how-to-trigger-lambda-from-s3
npx cdk init app --language typescript
This should give you the following directory structure.
Also make sure you have your AWS CLI configured. For more information follow the AWS CLI quickstart guide.
Create an S3 Bucket
Install the S3 CDK package.
npm i @aws-cdk/aws-s3
Open lib/how-to-trigger-lambda-from-s3-stack.ts
, add a new S3 Bucket, and deploy.
import * as cdk from '@aws-cdk/core';
import * as s3 from '@aws-cdk/aws-s3';
export class HowToTriggerLambdaFromS3Stack extends cdk.Stack {
constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
super(scope, id, props);
const bucket = new s3.Bucket(this, 'OurBucket', {
/**
* The following properties ensure the bucket is properly
* deleted when we run cdk destroy */
autoDeleteObjects: true,
removalPolicy: cdk.RemovalPolicy.DESTROY
})
}
}
npm run cdk deploy
You may need to confirm some IAM changes.
Create a Lambda
Install the Lambda CDK package.
npm i @aws-cdk/aws-lambda
Deploying a Lambda function requires bootstrapping your CDK app which gives us an S3 bucket where our Lambda's source code will live. This is a one time operation.
npm run cdk bootstrap
Create src/index.js and paste the following code
exports.handler = async (event) => {
event.Records.forEach((record) => {
console.log('Event Name: %s', record.eventName);
console.log('S3 Request: %j', record.s3);
});
};
Open lib/how-to-trigger-lambda-from-s3-stack.ts
, add a new Lambda function, and deploy.
import * as cdk from '@aws-cdk/core';
import * as s3 from '@aws-cdk/aws-s3';
import * as lambda from '@aws-cdk/aws-lambda';
export class HowToTriggerLambdaFromS3Stack extends cdk.Stack {
constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
super(scope, id, props);
const bucket = new s3.Bucket(this, 'OurBucket', {
/**
* The following properties ensure the bucket is properly
* deleted when we run cdk destroy */
autoDeleteObjects: true,
removalPolicy: cdk.RemovalPolicy.DESTROY
});
const lambdaFunction = new lambda.Function(this, 'Function', {
code: lambda.Code.fromAsset('src'),
handler: 'index.handler',
functionName: 'BucketPutHandler',
runtime: lambda.Runtime.NODEJS_12_X,
});
}
}
Deploy again ...
npm run cdk deploy
You may need to confirm more IAM changes.
Create the Event Source
Install the Lambda Event Sources CDK package.
npm i @aws-cdk/aws-lambda-event-sources
Open lib/how-to-trigger-lambda-from-s3-stack.ts, add a new S3EventSource to the Lambda Function.
import * as cdk from '@aws-cdk/core';
import * as s3 from '@aws-cdk/aws-s3';
import * as lambda from '@aws-cdk/aws-lambda';
import * as lambdaEventSources from '@aws-cdk/aws-lambda-event-sources';
export class HowToTriggerLambdaFromS3Stack extends cdk.Stack {
constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
super(scope, id, props);
const bucket = new s3.Bucket(this, 'OurBucket', {
/**
* The following properties ensure the bucket is properly
* deleted when we run cdk destroy */
autoDeleteObjects: true,
removalPolicy: cdk.RemovalPolicy.DESTROY
});
const lambdaFunction = new lambda.Function(this, 'Function', {
code: lambda.Code.fromAsset('src'),
handler: 'index.handler',
functionName: 'BucketPutHandler',
runtime: lambda.Runtime.NODEJS_12_X,
});
const s3PutEventSource = new lambdaEventSources.S3EventSource(bucket, {
events: [
s3.EventType.OBJECT_CREATED_PUT
]
});
lambdaFunction.addEventSource(s3PutEventSource);
}
}
One more deployment ...
npm run cdk deploy
One last time, you may need to approve IAM changes.
Testing
Create a text file that we will use to upload to the S3 bucket.
echo "This is a test" > testFile.txt
Use the AWS CLI to upload this file into our S3 bucket from earlier. Your bucket name will vary, but for me this command looks like this.
aws s3 cp ./testFile.txt s3://howtotriggerlambdafroms3stack-ourbucket48caf57c-1p9g74rol1cza/testFile.txt
Verify that the Lambda executed by looking in CloudWatch. Find the LogGroup named /aws/lambda/BucketPutHandler
and open up the latest LogStream. You should see some log messages that look similar to this.
Clean Up
Don't forget to delete your stack when you are finished!
npm run cdk destroy
Thanks for reading! If you found this useful, please follow me here
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Top comments (2)
Helpful!
This is all good and all but I need it to run as a single rerunnable deployment script