Getting started with AWS SAM and the AWS CDK

This topic describes what you need to use the AWS SAM CLI with AWS CDK applications, and provides instructions for building and locally testing a simple AWS CDK application.

Prerequisites

To use the AWS SAM CLI with AWS CDK, you must install the AWS CDK, and the AWS SAM CLI.

• For information about installing the AWS CDK, see Getting started with the AWS CDK in the AWS Cloud Development Kit (AWS CDK) Developer Guide.

• For information about installing the AWS SAM CLI, see Install the AWS SAM CLI.

Creating and locally testing an AWS CDK application

To locally test an AWS CDK application using the AWS SAM CLI, you must have an AWS CDK application that contains a Lambda function. Use the following steps to create a basic AWS CDK application with a Lambda function. For more information, see Creating a serverless application using the AWS CDK in the AWS Cloud Development Kit (AWS CDK) Developer Guide.

Note

The AWS SAM CLI supports AWS CDK v1 starting from version 1.135.0 and AWS CDK v2 starting from version 2.0.0.

Step 1: Create an AWS CDK application

For this tutorial, initialize an AWS CDK application that uses TypeScript.

Command to run:

AWS CDK v2

mkdir cdk-sam-example
cd cdk-sam-example
cdk init app --language typescript

AWS CDK v1

mkdir cdk-sam-example
cd cdk-sam-example
cdk init app --language typescript
npm install @aws-cdk/aws-lambda

Step 2: Add a Lambda function to your application

Replace the code in lib/cdk-sam-example-stack.ts with the following:

AWS CDK v2

import { Stack, StackProps } from 'aws-cdk-lib';
import { Construct } from 'constructs';
import * as lambda from 'aws-cdk-lib/aws-lambda';

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

    new lambda.Function(this, 'MyFunction', {
      runtime: lambda.Runtime.PYTHON_3_9,
      handler: 'app.lambda_handler',
      code: lambda.Code.fromAsset('./my_function'),
    });
  }
}

AWS CDK v1

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

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

    new lambda.Function(this, 'MyFunction', {
      runtime: lambda.Runtime.PYTHON_3_9,
      handler: 'app.lambda_handler',
      code: lambda.Code.fromAsset('./my_function'),
    });
  }
}

Step 3: Add your Lambda function code

Create a directory named my_function. In that directory, create a file named app.py.

Command to run:

mkdir my_function
cd my_function
touch app.py

Add the following code to app.py:

def lambda_handler(event, context):
    return "Hello from SAM and the CDK!"

Step 4: Test your Lambda function

You can use the AWS SAM CLI to locally invoke a Lambda function that you define in an AWS CDK application. To do this, you need the function construct identifier and the path to your synthesized AWS CloudFormation template.

Command to run:

cdk synth --no-staging

sam local invoke MyFunction --no-event -t ./cdk.out/CdkSamExampleStack.template.json

Example output:

Invoking app.lambda_handler (python3.9)
     
START RequestId: 5434c093-7182-4012-9b06-635011cac4f2 Version: $LATEST
"Hello from SAM and the CDK!"
END RequestId: 5434c093-7182-4012-9b06-635011cac4f2
REPORT RequestId: 5434c093-7182-4012-9b06-635011cac4f2	Init Duration: 0.32 ms	Duration: 177.47 ms	Billed Duration: 178 ms	Memory Size: 128 MB	Max Memory Used: 128 MB

For more information about options available to test AWS CDK applications using the AWS SAM CLI, see Locally testing AWS CDK applications with AWS SAM.