How to Create AWS CDK Lambda Functions? 4 Easy Steps

• May 23rd, 2022

AWS CDK Lambda - Featured Image

When you start building a cloud-based back-end system for your application, you can manually build it using the graphical user interface (GUI) or command-line interface (CLI) provided by the cloud provider to provision cloud resources. Though, this manual approach is prone to human error and cannot be performed in a repeatable, reliable, or consistent manner due to the need for manual intervention. A popular solution is using an open-source software development framework like AWS CDK.

This comes with AWS Lamda which allows you to simply focus on your code while it manages and maintains your server resources. You can design your code into AWS CDK Lambda functions that process the events that you pass into the function. You can invoke your AWS CDK Lambda function via the Lambda API, or configure an AWS service or resource to run your function.

In this article, you will learn how to effectively create and deploy your AWS CDK Lambda function in 4 easy steps.

Table of Contents

What is AWS CDK?

AWS CDK Lambda - AWS CDK Logo
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The Amazon Web Services Cloud Development Kit (AWS CDK) is an open-source software development framework that allows you to easily define the cloud infrastructure needed for your application. You can do this using popular programming languages such as JavaScript, TypeScript, Python, Java & .NET. AWS CDK provides reusable cloud components called constructs that incorporate AWS best practices in your infrastructure definition. After you have modeled your application, you simply deploy it using AWS CloudFormation.    

What are AWS Lambda Functions?

AWS CDK Lambda - AWS CDK Lambda Function deployement
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AWS Lambda is a powerful compute service that allows you to run your code for virtually any type of application or backend service without worrying about configuring or managing servers. You can simply organize your application code in AWS CDK Lambda functions. To create or invoke your AWS CDK Lambda functions, you can use the AWS Lambda API or console. After creating your AWS CDK Lambda function, you can set multiple function capabilities and options such as permissions, environment variables, tags, and layers.

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Understanding the Salient Aspects of AWS Lambda Construct Library

The AWS construct library contains modules for each AWS service with constructs that provide an API that encapsulates the details of AWS usage. The AWS Construct Library reduces the complexity and connection logic required when integrating various AWS services to achieve your goals on AWS. You can check out the following aspects of the AWS Lambda construct library: 

Docker Images

You specify the Lambda function’s handlers within docker images. The docker image can be an image from ECR or a local asset that the CDK will package and load into ECR. 

  • To understand this, observe the DockerImageFunction construct that uses a local folder with a Dockerfile as the asset that will be used as the AWS CDK Lambda function handler.
new lambda.DockerImageFunction(this, 'AssetFunction', {
  code: lambda.DockerImageCode.fromImageAsset(path.join(__dirname, 'docker-handler')),
  • Apart from the local asset, you can follow the example given below to specify an image that already exists in ECR as the AWS CDK Lambda Function handler.
import * as ecr from '@aws-cdk/aws-ecr';
const repo = new ecr.Repository(this, 'Repository');

new lambda.DockerImageFunction(this, 'ECRFunction', {
  code: lambda.DockerImageCode.fromEcr(repo),

It is important to note that these docker image resources allow overriding the image’s CMD, ENTRYPOINT, and WORKDIR configurations and choosing a specific tag or digest.

Handler Code

You can deploy your code using lambda.Code class. This class has the following methods for different types of runtime code:

  • lambda.Code.fromBucket(bucket, key[, objectVersion]): Denotes the S3 object that has the archive of your runtime code.
  • lambda.Code.fromInline(code): You can use this to inline the handle code as a string. 
  • lambda.Code.fromAsset(path): This allows you to mention a directory or a .zip file in your local filesystem which will be zipped and uploaded to S3 before deployment. 
  • lambda.Code.fromDockerBuild(path, options): You can also use the result of a Docker build as code. Generally, the code is present at /asset in the image and will be zipped and uploaded to S3 as an asset.

For instance, you can go through the following python AWS CDK Lambda function example that deploys the code from the local directory new-aws-lambda-handler to it. Note that during synthesis, the CDK expects to find a directory on disk at the asset directory specified. 

new lambda.Function(this, 'NewLambda', {
  code: lambda.Code.fromAsset(path.join(__dirname, 'new-aws-lambda-handler')),
  handler: 'index.main',
  runtime: lambda.Runtime.PYTHON_3_6,

Function Timeout

With a default timeout of 3 seconds, AWS CDK Lambda functions allow you to increase it up to 15 minutes. You can reference this property elsewhere in your stack, for example, to create a CloudWatch alarm to report when your function timed out:

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

const fn = new lambda.Function(this, 'NewFunction', {
   runtime: lambda.Runtime.NODEJS_16_X,
   handler: 'index.handler',
   code: lambda.Code.fromAsset(path.join(__dirname, 'new-aws-lambda-handler')),
   timeout: cdk.Duration.minutes(5),

if (fn.timeout) {
   new cloudwatch.Alarm(this, `NewAlarm`, {
      metric: fn.metricDuration().with({
         statistic: 'Maximum',
      evaluationPeriods: 1,
      datapointsToAlarm: 1,
      threshold: fn.timeout.toMilliseconds(),
      treatMissingData: cloudwatch.TreatMissingData.IGNORE,
      alarmName: 'New Timeout',

Execution Role

AWS CDK Lambda functions assume an IAM(Identity and Access Management) role during runtime. By Default, AWS CDK Lambda functions will assume an autogenerated Role if you have not assigned it. Moreover, the autogenerated Role is automatically given permissions to run the Lambda function. You can use the following commands to reference the autogenerated Role:

const fn = new lambda.Function(this, 'NewFunction', {
  runtime: lambda.Runtime.NODEJS_16_X,
  handler: 'index.handler',
  code: lambda.Code.fromAsset(path.join(__dirname, 'new-aws-lambda-handler')),
const role = fn.role; // the Role

For better control, you can also provide your own IAM role, though permission will not automatically be granted to run the AWS CDK Lambda function. You can provide a role and grant it appropriate permissions by following the example given below: 

const myRole = new iam.Role(this, 'My Role', {
  assumedBy: new iam.ServicePrincipal(''),
const fn = new lambda.Function(this, 'NewFunction', {
  runtime: lambda.Runtime.NODEJS_16_X,
  handler: 'index.handler',
  code: lambda.Code.fromAsset(path.join(__dirname, 'new-aws-lambda-handler')),
  role: myRole, // user-provided role
myRole.addManagedPolicy(iam.ManagedPolicy.fromAwsManagedPolicyName("service-role/AWSLambdaVPCAccessExecutionRole")); // only required if your function lives in a VPC

Resource-based Policies

AWS Lambda supports resource-based policies to control access to AWS CDK Lambda functions and tiers on a per-resource basis. Moreover, it gives AWS services and other AWS accounts the right to change and call functions. You can also limit AWS service permissions by specifying a source account or ARN(Amazon Resource Name).

declare const fn: lambda.Function;
const principal = new iam.ServicePrincipal('my-service');


// Equivalent to:
fn.addPermission('my-service Invocation', {
  principal: principal,


You will observe that by default AWS CDK Lambda functions run on compute systems that have the 64-bit x86 architecture. They also run on the ARM architecture, which can reduce costs for some workloads. Depending on your requirement, you can configure an AWS CDK Lambda function can be configured to be run on one of these platforms:

new lambda.Function(this, 'NewFunction', {
  runtime: lambda.Runtime.NODEJS_16_X,
  handler: 'index.handler',
  code: lambda.Code.fromAsset(path.join(__dirname, 'new-aws-lambda-handler')),
  architecture: lambda.Architecture.ARM_64,

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Steps to create a Lambda Function in AWS CDK

To create and deploy an AWS CDK Lambda function. You can follow the easy steps given below:

Step 1: Instantiate Function Class

To create the AWS CDK Lambda Function, you have first instantiate the Function class.

import * as iam from 'aws-cdk-lib/aws-iam';
import * as lambda from 'aws-cdk-lib/aws-lambda';
import * as cdk from 'aws-cdk-lib';
import * as path from 'path';

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

    //  lambda function definition
    const lambdaFunction = new lambda.Function(this, 'lambda-function', {
      runtime: lambda.Runtime.NODEJS_14_X,
      memorySize: 1024,
      timeout: cdk.Duration.seconds(5),
      handler: 'index.main',
      code: lambda.Code.fromAsset(path.join(__dirname, '/../src/new-lambda')),
      environment: {
        REGION: cdk.Stack.of(this).region,
        AVAILABILITY_ZONES: JSON.stringify(

The above function configuration required the following properties:

  • runtime: Represents the programming language and version used for the AWS CDK Lambda function.
  • memorySize: 128 MB being the default value, this represents the amount of memory you want to allocate to the function. 
  • timeout: The time your function has to run before it is terminated.
  • handler: This denotes the file storing the lambda function named index.js and the handler function that is named main.
  • code: The source code of the lambda function.
  • environment: A complete map of your environment variables.

Step 2: Add the code for the Lambda Function

After instantiating the function class, now you can add the code for the AWS CDK Lambda function at src/new-lambda/index.js:

async function main(event) {
  console.log('region 👉', process.env.REGION);
  console.log('availability zones 👉', process.env.AVAILABILITY_ZONES);

  return {
    body: JSON.stringify({message: 'SUCCESS 🎉'}),
    statusCode: 200,

module.exports = {main};

Step 3: Adding IAM Permissions for Lambda Function

As discussed in the above section, IAM roles are automatically assigned for your AWS CDK Lambda functions. You can also view the already added CloudWatch logging permissions for your autogenerated role:

AWS CDK Lambda - CloudWatch logging permissions
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You can simply add permissions to an AWS CDK Lambda function by attaching policies to the auto-generated role of the function. For instance, you can add a permission to list all of the S3 buckets in the account:

import * as iam from 'aws-cdk-lib/aws-iam';
import * as lambda from 'aws-cdk-lib/aws-lambda';
import * as cdk from 'aws-cdk-lib';
import * as path from 'path';

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

    // ... rest

    // 👇 create a policy statement
    const listBucketsPolicy = new iam.PolicyStatement({
      effect: iam.Effect.ALLOW,
      actions: ['s3:ListAllMyBuckets'],
      resources: ['arn:aws:s3:::*'],

    // 👇 attach the policy to the function's role
      new iam.Policy(this, 'list-buckets', {
        statements: [listBucketsPolicy],

Here, you have created a policy statement that allows the s3:ListAllMyBuckets action on all s3 resources and then successfully attached the policy to the role of the AWS CDK Lambda function.

Step 4: Deploy the Function

Finally, you can deploy the AWS CDK Lambda function using the following command: 

npx aws-cdk deploy

To check if the desired permissions are added, you can navigate to the IAM management console and verify the role of the AWS CDK Lambda function. You will find that 2 permission policies are attached now, including the one that grants the s3:ListAllMyBuckets action.

AWS CDK Lambda - new permissions
Image Source


In this article, you have learned how to effectively create and deploy an AWS CDK Lambda function. AWS Lambda allows you to simply run your code as it manages the compute fleet that offers a balance of memory, CPU, network, and other resources for executing your code. It takes care of the operational and administrative activities on your behalf, including managing capacity, monitoring, and logging your AWS CDK Lambda functions. Using the AWS Lambda API or console, you can easily create, configure the additional properties and deploy them using programming languages such as JavaScript, TypeScript, Python, Java & .NET.

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Share your experience of creating and deploying AWS CDK Lambda functions! Let us know in the comments section below!

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