Amazon Lambda function logging in TypeScript

Initialize the application using the Hello World TypeScript template.

sam init --app-template hello-world-powertools-typescript --name sam-app --package-type Zip --runtime nodejs18.x

Build the app.

cd sam-app && sam build

Deploy the app.

sam deploy --guided

Follow the on-screen prompts. To accept the default options provided in the interactive experience, press Enter.

Get the URL of the deployed application:

aws cloudformation describe-stacks --stack-name sam-app --query 'Stacks[0].Outputs[?OutputKey==`HelloWorldApi`].OutputValue' --output text

Invoke the API endpoint:

curl <URL_FROM_PREVIOUS_STEP>

If successful, you'll see this response:

{"message":"hello world"}

To get the logs for the function, run sam logs. For more information, see Working with logs in the Amazon Serverless Application Model Developer Guide.

sam logs --stack-name sam-app

The log output looks like this:

2023/01/31/[$LATEST]4d53e8d279824834a1ccd35511a4949c 2022-08-31T09:33:10.552000 START RequestId: 70693159-7e94-4102-a2af-98a6343fb8fb Version: $LATEST
2023/01/31/[$LATEST]4d53e8d279824834a1ccd35511a4949c 2022-08-31T09:33:10.594000 2022-08-31T09:33:10.557Z 70693159-7e94-4102-a2af-98a6343fb8fb INFO {"_aws":{"Timestamp":1661938390556,"CloudWatchMetrics":[{"Namespace":"sam-app","Dimensions":[["service"]],"Metrics":[{"Name":"ColdStart","Unit":"Count"}]}]},"service":"helloWorld","ColdStart":1}
2023/01/31/[$LATEST]4d53e8d279824834a1ccd35511a4949c 2022-08-31T09:33:10.595000 2022-08-31T09:33:10.595Z 70693159-7e94-4102-a2af-98a6343fb8fb INFO {"level":"INFO","message":"This is an INFO log - sending HTTP 200 - hello world response","service":"helloWorld","timestamp":"2022-08-31T09:33:10.594Z"}
2023/01/31/[$LATEST]4d53e8d279824834a1ccd35511a4949c 2022-08-31T09:33:10.655000 2022-08-31T09:33:10.655Z 70693159-7e94-4102-a2af-98a6343fb8fb INFO {"_aws":{"Timestamp":1661938390655,"CloudWatchMetrics":[{"Namespace":"sam-app","Dimensions":[["service"]],"Metrics":[]}]},"service":"helloWorld"}
2023/01/31/[$LATEST]4d53e8d279824834a1ccd35511a4949c 2022-08-31T09:33:10.754000 END RequestId: 70693159-7e94-4102-a2af-98a6343fb8fb
2023/01/31/[$LATEST]4d53e8d279824834a1ccd35511a4949c 2022-08-31T09:33:10.754000 REPORT RequestId: 70693159-7e94-4102-a2af-98a6343fb8fb Duration: 201.55 ms Billed Duration: 202 ms Memory Size: 128 MB Max Memory Used: 66 MB Init Duration: 252.42 ms
XRAY TraceId: 1-630f2ad5-1de22b6d29a658a466e7ecf5 SegmentId: 567c116658fbf11a Sampled: true

This is a public API endpoint that is accessible over the internet. We recommend that you delete the endpoint after testing.

sam delete

Create a project directory for your new application.

mkdir hello-world
cd hello-world

Initialize the app.

cdk init app --language typescript

Add the @types/aws-lambda package as a development dependency.

npm install -D @types/aws-lambda

Install the Powertools Logger utility.

npm install @aws-lambda-powertools/logger

Open the lib directory. You should see a file called hello-world-stack.ts. Create new two new files in this directory: hello-world.function.ts and hello-world.ts.

Open hello-world.function.ts and add the following code to the file. This is the code for the Lambda function.

import { APIGatewayEvent, APIGatewayProxyResult, Context } from 'aws-lambda';
import { Logger } from '@aws-lambda-powertools/logger';
const logger = new Logger();
  
export const handler = async (event: APIGatewayEvent, context: Context): Promise<APIGatewayProxyResult> => {
  logger.info('This is an INFO log - sending HTTP 200 - hello world response');
  return {
    statusCode: 200,
    body: JSON.stringify({
      message: 'hello world',
    }),
  };
};

Open hello-world.ts and add the following code to the file. This contains the NodejsFunction construct, which creates the Lambda function, configures environment variables for Powertools, and sets log retention to one week. It also includes the LambdaRestApi construct, which creates the REST API.

import { Construct } from 'constructs';
import { NodejsFunction } from 'aws-cdk-lib/aws-lambda-nodejs';
import { LambdaRestApi } from 'aws-cdk-lib/aws-apigateway';
import { RetentionDays } from 'aws-cdk-lib/aws-logs';
import { CfnOutput } from 'aws-cdk-lib';
  
export class HelloWorld extends Construct {
  constructor(scope: Construct, id: string) {
    super(scope, id);
    const helloFunction = new NodejsFunction(this, 'function', {
      environment: {
        Powertools_SERVICE_NAME: 'helloWorld',
        LOG_LEVEL: 'INFO',
      },
      logRetention: RetentionDays.ONE_WEEK,
    });
    const api = new LambdaRestApi(this, 'apigw', {
      handler: helloFunction,
    });
    new CfnOutput(this, 'apiUrl', {
      exportName: 'apiUrl',
      value: api.url,
    });
  }
}

Open hello-world-stack.ts. This is the code that defines your Amazon CDK stack. Replace the code with the following:

import { Stack, StackProps } from 'aws-cdk-lib';
import { Construct } from 'constructs';
import { HelloWorld } from './hello-world';
    
export class HelloWorldStack extends Stack {
  constructor(scope: Construct, id: string, props?: StackProps) {
    super(scope, id, props);
    new HelloWorld(this, 'hello-world');
  }
}

Go back to the project directory.

cd hello-world

Deploy your application.

cdk deploy

Get the URL of the deployed application:

aws cloudformation describe-stacks --stack-name HelloWorldStack --query 'Stacks[0].Outputs[?ExportName==`apiUrl`].OutputValue' --output text

Invoke the API endpoint:

curl <URL_FROM_PREVIOUS_STEP>

If successful, you'll see this response:

{"message":"hello world"}

To get the logs for the function, run sam logs. For more information, see Working with logs in the Amazon Serverless Application Model Developer Guide.

sam logs --stack-name HelloWorldStack

The log output looks like this:

2023/01/31/[$LATEST]2ca67f180dcd4d3e88b5d68576740c8e 2022-08-31T14:48:37.047000 START RequestId: 19ad1007-ff67-40ce-9afe-0af0a9eb512c Version: $LATEST
2023/01/31/[$LATEST]2ca67f180dcd4d3e88b5d68576740c8e 2022-08-31T14:48:37.050000 {
"level": "INFO",
"message": "This is an INFO log - sending HTTP 200 - hello world response",
"service": "helloWorld",
"timestamp": "2022-08-31T14:48:37.048Z",
"xray_trace_id": "1-630f74c4-2b080cf77680a04f2362bcf2"
}
2023/01/31/[$LATEST]2ca67f180dcd4d3e88b5d68576740c8e 2022-08-31T14:48:37.082000 END RequestId: 19ad1007-ff67-40ce-9afe-0af0a9eb512c
2023/01/31/[$LATEST]2ca67f180dcd4d3e88b5d68576740c8e 2022-08-31T14:48:37.082000 REPORT RequestId: 19ad1007-ff67-40ce-9afe-0af0a9eb512c Duration: 34.60 ms Billed Duration: 35 ms Memory Size: 128 MB Max Memory Used: 57 MB Init Duration: 173.48 ms

This is a public API endpoint that is accessible over the internet. We recommend that you delete the endpoint after testing.

cdk destroy

Open the Log groups page on the CloudWatch console.

Choose the log group for your function (/aws/lambda/your-function-name).

Choose a log stream.