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SAM CLI

This topic describes how to use the AWS SAM CLI with the AWS CDK to test a Lambda function locally. For further information, see Invoking Functions Locally. To install the SAM CLI, see Installing the AWS SAM CLI.

  1. The first step is to create a AWS CDK application and add the Lambda package.

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

  2. Add a Lambda reference to lib/cdk-sam-example-stack.ts:

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

  3. Replace the comment in lib/cdk-sam-example-stack.ts with the following Lambda function:

    new lambda.Function(this, 'MyFunction', {
  runtime: lambda.Runtime.PYTHON_3_7,
  handler: 'app.lambda_handler',
  code:    lambda.Code.asset('./my_function'),
});

  4. Create the directory my_function

    mkdir my_function

  5. Create the file app.py in my_function with the following content:

    def lambda_handler(event, context):
  return "This is a Lambda Function defined through CDK"

  6. Run your AWS CDK app and create a AWS CloudFormation template

    cdk synth --no-staging > template.yaml

  7. Find the logical ID for your Lambda function in template.yaml. It will look like MyFunction12345678, where 12345678 represents an 8-character unique ID that the AWS CDK generates for all resources. The line right after it should look like:

    Type: AWS::Lambda::Function

  8. Run the function by executing:

    sam local invoke MyFunction12345678 --no-event

    The output should look something like the following.

    2019-04-01 12:22:41 Found credentials in shared credentials file: ~/.aws/credentials
2019-04-01 12:22:41 Invoking app.lambda_handler (python3.7)

Fetching lambci/lambda:python3.7 Docker container image......
2019-04-01 12:22:43 Mounting D:\cdk-sam-example\.cdk.staging\a57f59883918e662ab3c46b964d2faa5 as /var/task:ro,delegated inside runtime container
START RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 Version: $LATEST
END RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72
REPORT RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72     Duration: 3.70 ms       Billed Duration: 100 ms Memory Size: 128 MB     Max Memory Used: 22 MB

"This is a Lambda Function defined through CDK"