# Task 2: Build a Serverless Function
<a name="module-two"></a>


|  |  | 
| --- |--- |
|  **Time to complete**  |  5 minutes   | 
|  **Services used**  |  [AWS Lambda](https://aws.amazon.com/lambda/)  [AWS Amplify](https://aws.amazon.com/amplify/)   | 
|  **Requires**  |  A text editor. Here are a few free ones:  [\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/hands-on/latest/build-web-app-s3-lambda-api-gateway-dynamodb/module-two.html)  | 
|  **Get help**  |  [Learn more about functions](https://docs.amplify.aws/react/build-a-backend/functions/)   | 

## Overview
<a name="overview"></a>

Now that you have a React web app, you will use AWS Amplify and AWS Lambda to configure a serverless function. This function is invoked after a signed-up user confirms their user account. AWS Lambda is a compute service that runs your code in response to events and automatically manages the compute resources, making it the fastest way to turn an idea into a modern, production, serverless applications. 

## Key concepts
<a name="key-concepts"></a>

**Serverless function:** Piece of code that will be executed by a compute service, on demand. 

## Implementation
<a name="implementation"></a>

### Step 1: Set up an Amplify Function
<a name="set-up-an-amplify-function"></a>

1. Create files

   On your local machine, navigate to the **profilesapp/amplify/auth** folder. 

   **Create** a new folder inside the **amplify/auth** folder and name it ****post-confirmation****. 

   **Create** the files named **resource.ts** and **handler.ts** inside the folder.   
![\[A sample file structure for a basic web application tutorial, showing folders such as amplify, auth, and data, with TypeScript files like handler.ts and resource.ts highlighted under post-confirmation in the auth folder.\]](http://docs.aws.amazon.com/hands-on/latest/build-web-app-s3-lambda-api-gateway-dynamodb/images/basic-file-structure-ace-sample-folders.png)

1. Update the resources file

   **Update** the **amplify/auth/post-confirmation/resource.ts** file with the following code to define the **postConfirmation** function. Then, **save** the file. 

   ```
   import { defineFunction } from '@aws-amplify/backend'; 
   export const postConfirmation = defineFunction({ 
     name: 'post-confirmation',
   });
   ```  
![\[The file structure for a web application project, highlighting the update to 'resource.ts' in the amplify/auth/post-confirmation directory. Used in the 'Build a Basic Web Application' tutorial.\]](http://docs.aws.amazon.com/hands-on/latest/build-web-app-s3-lambda-api-gateway-dynamodb/images/basic-update-resource-file-structure.png)

1. Update the handler file

   **Update** the **amplify/auth/post-confirmation/handler.ts **file with the following code to define the function’s handler. Then, **save** the file. 

   ```
   import type { PostConfirmationTriggerHandler } from "aws-lambda"; 
   export const handler: PostConfirmationTriggerHandler = async (event) => { 
     return event;
   };
   ```  
![\[The folder structure of a web application project, highlighting the 'handler.ts' file in the 'amplify/auth/post-confirmation' directory. This illustrates the step to update the handler file as part of building a basic web application tutorial.\]](http://docs.aws.amazon.com/hands-on/latest/build-web-app-s3-lambda-api-gateway-dynamodb/images/fmpdokb-basic-update-handler-file-folder.png)

## Conclusion
<a name="conclusion"></a>

You have defined a Lambda function using Amplify.