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lambda-nodejs.md

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Building Lambda functions with Node.js

You can run JavaScript code with Node.js in AWS Lambda. Lambda provides runtimes for Node.js that execute your code to process events. Your code runs in an environment that includes the AWS SDK for JavaScript, with credentials from an AWS Identity and Access Management (IAM) role that you manage.

Lambda supports the following Node.js runtimes.

Node.js runtimes

Name Identifier AWS SDK for JavaScript Operating system
Node.js 12 nodejs12.x 2.631.0 Amazon Linux 2
Node.js 10 nodejs10.x 2.631.0 Amazon Linux 2

Lambda functions use an execution role to get permission to write logs to Amazon CloudWatch Logs, and to access other services and resources. If you don't already have an execution role for function development, create one.

To create an execution role

  1. Open the roles page in the IAM console.

  2. Choose Create role.

  3. Create a role with the following properties.

    • Trusted entity – Lambda.
    • Permissions – AWSLambdaBasicExecutionRole.
    • Role name – lambda-role.

    The AWSLambdaBasicExecutionRole policy has the permissions that the function needs to write logs to CloudWatch Logs.

You can add permissions to the role later, or swap it out for a different role that's specific to a single function.

To create a Node.js function

  1. Open the Lambda console.

  2. Choose Create function.

  3. Configure the following settings:

    • Name – my-function.
    • Runtime – Node.js 12.x.
    • Role – Choose an existing role.
    • Existing role – lambda-role.

  4. Choose Create function.

  5. To configure a test event, choose Test.

  6. For Event name, enter test.

  7. Choose Create.

  8. To execute the function, choose Test.

The console creates a Lambda function with a single source file named index.js. You can edit this file and add more files in the built-in code editor. To save your changes, choose Save. Then, to run your code, choose Test.

Note
The Lambda console uses AWS Cloud9 to provide an integrated development environment in the browser. You can also use AWS Cloud9 to develop Lambda functions in your own environment. For more information, see Working with AWS Lambda Functions in the AWS Cloud9 user guide.

The index.js file exports a function named handler that takes an event object and a context object. This is the handler function that Lambda calls when the function is invoked. The Node.js function runtime gets invocation events from Lambda and passes them to the handler. In the function configuration, the handler value is index.handler.

Each time you save your function code, the Lambda console creates a deployment package, which is a ZIP archive that contains your function code. As your function development progresses, you will want to store your function code in source control, add libraries, and automate deployments. Start by creating a deployment package and updating your code at the command line.

Note
To get started with application development in your local environment, deploy one of the sample applications available in this guide's GitHub repository.
blank-nodejs – A Node.js function that shows the use of logging, environment variables, AWS X-Ray tracing, layers, unit tests and the AWS SDK. nodejs-apig – A function with a public API endpoint that processes an event from API Gateway and returns an HTTP response. rds-mysql – A function that relays queries to a MySQL for RDS Database. This sample includes a private VPC and database instance configured with a password in AWS Secrets Manager. efs-nodejs – A function that uses an Amazon EFS file system in a Amazon VPC. This sample includes a VPC, file system, mount targets, and access point configured for use with Lambda. list-manager – A function processes events from an Amazon Kinesis data stream and update aggregate lists in Amazon DynamoDB. The function stores a record of each event in a MySQL for RDS Database in a private VPC. This sample includes a private VPC with a VPC endpoint for DynamoDB and a database instance. error-processor – A Node.js function generates errors for a specified percentage of requests. A CloudWatch Logs subscription invokes a second function when an error is recorded. The processor function uses the AWS SDK to gather details about the request and stores them in an Amazon S3 bucket.

The function runtime passes a context object to the handler, in addition to the invocation event. The context object contains additional information about the invocation, the function, and the execution environment. More information is available from environment variables.

Your Lambda function comes with a CloudWatch Logs log group. The function runtime sends details about each invocation to CloudWatch Logs. It relays any logs that your function outputs during invocation. If your function returns an error, Lambda formats the error and returns it to the invoker.

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