How to Build a Serverless Application on AWS

If you're looking to build a new application or migrate an existing one to the cloud, serverless architecture on AWS could be a great solution for you. With serverless, you don't have to worry about managing servers, scaling up or down, or provisioning resources. Instead, you can focus on writing code and delivering value to your users.

So, how do you get started building a serverless application on AWS? In this article, we'll walk through the basics of serverless architecture and showcase how to set up and deploy a serverless application on AWS.

What is Serverless Architecture?

Serverless architecture is a cloud computing model where the cloud provider manages the infrastructure and automatically allocates resources as needed. It is commonly used for building microservices, APIs, and event-driven processing. In serverless architecture, the application logic is broken down into small, independently deployable functions that run in a managed runtime environment.

One of the primary benefits of serverless architecture is that you only pay for the resources you consume, so it can be a cost-effective solution for many applications. Additionally, serverless applications are highly scalable and can handle sudden spikes in traffic without the need for additional resources.

Why use AWS for Serverless Architecture?

AWS offers a variety of services that support serverless architecture, including AWS Lambda, AWS API Gateway, AWS Step Functions, and more. These services work together to provide a fully managed serverless stack that allows developers to build, test, and deploy serverless applications quickly and easily.

AWS Lambda is a serverless compute service that lets you run code without provisioning or managing servers. It supports a variety of programming languages including Node.js, Python, Java, and more. With Lambda, you pay only for the compute time you consume, so it's a cost-effective solution for running small, short-lived functions.

AWS API Gateway is a fully managed service that makes it easy to create, publish, and manage APIs. It integrates with AWS Lambda to create a serverless API architecture that can scale automatically to handle any level of traffic. Additionally, API Gateway supports multiple protocols including HTTP, REST, and WebSocket, making it a versatile solution for building API-driven applications.

AWS Step Functions is a serverless workflow service that lets you coordinate distributed applications and microservices using visual workflows. It makes it easy to build complex workflows and handle different input and output formats without writing much code. With Step Functions, you can also easily incorporate AWS Lambda functions into your workflows.

How to Build a Serverless Application on AWS

Now, let's dive into how you can build a serverless application on AWS. In this example, we'll create a simple serverless application that reads data from Amazon S3 and sends it to a Slack channel.


Before we get started, make sure you have the following:

Step 1: Set up an S3 Bucket

Our serverless application needs to read data from an S3 bucket. To set up the S3 bucket, follow these steps:

  1. Log in to your AWS account and navigate to the S3 console.
  2. Click "Create bucket" and follow the prompts to create a new bucket.
  3. Upload a file to the S3 bucket. This could be any file - we'll just use a simple text file for this example.

Once you've completed these steps, note down the name of your S3 bucket. We'll need it later when we configure our Lambda function.

Step 2: Create a Slack Bot

Our serverless application will send data to a Slack channel using a Slack bot. To create a Slack bot, follow these steps:

  1. Log in to your Slack account and navigate to the "Apps" page.
  2. Click "Build" in the top right corner and select "Your apps".
  3. Click "Create New App" and follow the prompts to create a new app.
  4. Under the "Add features and functionality" section, click "Bots" and create a new bot user.
  5. Note down the bot token. We'll need it later when we configure our Lambda function.

Step 3: Set up a Lambda Function

Our serverless application will read data from the S3 bucket and send it to a Slack channel using a Lambda function. To set up the Lambda function, follow these steps:

  1. Open your terminal and run the following command to create a new serverless project:
$ serverless create --template aws-nodejs --path my-service
  1. Change into the "my-service" directory:
$ cd my-service
  1. Open the "serverless.yml" file and add the following to define a new Lambda function:
service: my-service
  name: aws
  runtime: nodejs14.x
    handler: handler.myFunction
      - s3:
          bucket: <YOUR S3 BUCKET NAME>
          event: s3:ObjectCreated:*
      - Effect: Allow
          - s3:GetObject
        Resource: arn:aws:s3:::<YOUR S3 BUCKET NAME>/*

In this configuration, we've defined a new Lambda function called "myFunction" that listens to the "s3:ObjectCreated:*" event on our S3 bucket. It also has an IAM role statement that allows it to read objects from the S3 bucket, and an environment variable that stores our Slack bot token.

  1. Create a new file called "handler.js" and add the following code:
const AWS = require('aws-sdk');
const Slack = require('slack');
const s3 = new AWS.S3({ apiVersion: '2006-03-01' });

exports.myFunction = async (event) => {
  const objectKey = event.Records[0].s3.object.key;
  const params = {
    Bucket: '<YOUR S3 BUCKET NAME>',
    Key: objectKey
  try {
    const data = await s3.getObject(params).promise();
    const message = {
      token: process.env.SLACK_BOT_TOKEN,
      channel: '<YOUR SLACK CHANNEL NAME>',
      text: `New file ${objectKey} uploaded to S3`
  } catch (error) {

In this code, we've defined the logic for our Lambda function. It reads the object key from the S3 event, retrieves the contents of the object from the S3 bucket, and sends a message to our Slack channel using the Slack API.

  1. Run the following command to deploy your Lambda function:
$ serverless deploy

Once the deployment is complete, note down the URL of your Lambda function endpoint. We'll need it later when configuring our S3 bucket.

Step 4: Set up S3 Event Notification

Our serverless application needs to be notified when a new file is uploaded to the S3 bucket. To set up S3 event notifications, follow these steps:

  1. Navigate to your S3 bucket and click the "Properties" tab.
  2. Click "Event notifications" and then click "Create Notification".
  3. Enter a name for the notification and select "All object create events".
  4. Under the "Send To" section, select "Lambda Function" and choose the Lambda function you deployed in the previous step.
  5. Click "Save".

Once you've completed these steps, your serverless application is ready to go! Whenever a new file is uploaded to your S3 bucket, it will trigger the Lambda function which will in turn send a message to your Slack channel.


Building a serverless application on AWS can be a quick and cost-effective way to get your application up and running in the cloud. With AWS Lambda, API Gateway, and Step Functions, you can build powerful applications without worrying about managing servers or scaling infrastructure.

In this article, we walked through the basics of serverless architecture and showed you how to set up and deploy a simple serverless application on AWS. With this knowledge, you can start building your own applications and taking advantage of the many benefits of serverless architecture on AWS. So, what are you waiting for? Get out there and start building!

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