Getting started with locally testing

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

Prerequisites

To test locally, you must install the AWS SAM CLI. see Install the AWS SAM CLI for installation instructions.

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.

Step 1: Create an AWS CDK application

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

Command to run:

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

Step 2: Add a Lambda function to your application

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

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_12,
      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.

Run the following command to go back to the lib directory:

$  cd ..

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