How to Build a Serverless Application on AWS

Are you ready to dive into the exciting world of serverless applications on AWS? In this tutorial, we'll guide you through the steps to build a fully functional serverless app on AWS using AWS Lambda, API Gateway, and DynamoDB. You'll learn how to create your Lambda function, define your API endpoints, and configure your database. So buckle up, and let's get started!

What is a Serverless Application on AWS?

First things first, let's get clear about what we mean by "serverless application." In a traditional application, you would have to provision a server, install an operating system, configure libraries, install dependencies, etc. But with serverless applications, you don't have to worry about any of that. You just write your code, deploy it to AWS, and let AWS take care of everything else.

With the AWS Serverless Application Model (SAM), you can define your serverless application using infrastructure as code. SAM provides a simplified way of defining the Amazon API Gateway APIs, AWS Lambda functions, and Amazon DynamoDB tables needed by your serverless application.

Setting up your AWS Environment

Before we dive into building our serverless application, we need to make sure we have our environment set up in AWS. Here are the steps:

1. Sign up for an AWS Account
2. Create an IAM User
3. Install the AWS CLI
4. Configure the AWS CLI

Don't worry if you've never done any of these before. AWS has clear documentation to guide you through each step.

Creating a Lambda Function

We'll start by creating a simple Lambda function that returns "Hello World" when called.

First, we'll create a zip file with our code in it. In our root directory, create a file called index.js, and paste the following code:

exports.handler = async (event, context) => {
    return {
        statusCode: 200,
        body: "Hello World"
    };
};

Now, let's zip the file by running the following command in our terminal:

zip function.zip index.js

Next, we'll create the Lambda function through the console. Navigate to the AWS Lambda service page, and click "Create function". Choose "Author from scratch", and give your function a name. For the runtime, we'll choose "Node.js 14.x", and for the execution role, choose "Create a new role with basic Lambda permissions."

In the Function code section, choose "Upload a .zip file", and upload our function.zip.

Finally, click "Create Function". Our Lambda function is now live on AWS! To test it out, click "Test" and choose "API Gateway AWS Proxy" as our Test Event. Click "Create", and then "Test" again. We should see "Hello World" returned in the response.

Giving our Lambda Function an API

Now that we have our Lambda function working, let's expose it through an API Gateway endpoint.

1. In the AWS Console, go to API Gateway.
2. Click "Create API".
3. Choose "REST API", and then "Build".
4. Choose a name for our API Gateway, and click "Create API".

Now we need to create a method for our Lambda function.

1. In the Resources section, click "Create Resource".
2. Choose "Create Method".
3. Choose "GET", and then "Lambda Function".
4. Choose our Lambda function in the drop-down menu, and click "Save".

Finally, let's deploy our API Gateway.

1. Click "Deploy API".
2. Choose a name for our deployment stage, and click "Deploy".

Our API Gateway is now live! In the Stages section, we can see our endpoint URL. Copy the URL, and paste it into a browser. We should see "Hello World" returned.

Storing Information in DynamoDB

Our final step will be to store and retrieve data from DynamoDB. First, we need to create a table.

1. In the AWS Console, go to DynamoDB.
2. Click "Create Table".
3. Choose a name for our table, and choose a primary key. For this example, we'll use "id" as our primary key.
4. Click "Create".

Now we need to modify our Lambda function to put and get data from our DynamoDB table.

1. In the AWS Console, go to Lambda.
2. Choose our Lambda function, and click "Add Trigger".
3. Choose "API Gateway", and select the API Gateway we created earlier.
4. Choose "Create a new API Gateway", and click "Add".

Next, we'll install the AWS SDK for Node.js in our project.

npm install aws-sdk

Now let's modify our Lambda function to put and retrieve data from our DynamoDB table.

const AWS = require("aws-sdk");

const dynamodb = new AWS.DynamoDB();

exports.handler = async (event, context) => {
    const id = Date.now().toString();
    const item = {
        id: { S: id },
        message: { S: "Hello World" }
    };

    await dynamodb.putItem({
        TableName: "serverless-demo-table",
        Item: item
    }).promise();

    const data = await dynamodb.getItem({
        TableName: "serverless-demo-table",
        Key: {
            id: { S: id }
        }
    }).promise();

    return {
        statusCode: 200,
        body: JSON.stringify(data.Item.message.S)
    };
};

We're generating a unique id for each item we put in the table, and storing a "Hello World" message as a string. We then put the item in our DynamoDB table, and retrieve the message back in our response.

Let's redeploy our Lambda function, and test our API Gateway, just like we did earlier. This time, we should see our "Hello World" message stored in our DynamoDB table, and retrieved via our API Gateway endpoint.

Conclusion

Congratulations! You've built a fully functional serverless application on AWS. You've created a Lambda function, exposed it through API Gateway, and stored and retrieved data from DynamoDB. We hope this tutorial has provided you with a solid foundation to build your own serverless applications on AWS. Happy coding!

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