Build a Basic Web Application


In this module, you will deploy your serverless function using Amazon API Gateway


In this module, we will use Amazon API Gateway to create a RESTful API that will allow us to make calls to our Lambda function from a web client (typically refers to a user's web browser). API Gateway will act as a middle layer between the HTML client we created in module one and the serverless backend we created in module two.

What you will accomplish

In this module, you will:

  • Create a new API using API Gateway
  • Define HTTP methods on your API
  • Trigger a Lambda function from an API
  • Enable cross-origin resource sharing (CORS) on an API so you can consume resources from a different origin (domain)
  • Test an API created with API Gateway from the AWS Management Console

Key concepts

RESTful API – REST stands for "Representational State Transfer" and is an architectural pattern for creating web services. API stands for "application programming interface." Thus, a RESTful API is one that implements the REST architectural pattern.

HTTP request methods – HTTP methods are designed to enable communications between clients and servers. Methods, like GET or PUT defined by the HTTP protocol, are used to indicate what action to take on a resource.

CORS – The CORS browser security feature uses HTTP headers to tell a browser to allow a given web application running at one origin (domain) to access selected resources from a server at a different origin.

Edge optimized – A resource that uses AWS global infrastructure to better serve geographically diverse clients.

 Minimum time to complete

5 minutes

 Services used

 Last updated

April 4, 2023


    1. Log in to the API Gateway console.
    2. In the Choose an API type section, find the REST API card and choose the Build button on the card.
    3. Under Choose the protocol, select REST.
    4. Under Create new API, select New API.
    5. In the API name field, enter HelloWorldAPI.
    6. Select Edge optimized from the Endpoint Type dropdown. (Note: Edge-optimized endpoints are best for geographically distributed clients. This makes them a good choice for public services being accessed from the internet. Regional endpoints are typically used for APIs that are accessed primarily from within the same AWS Region.)
    7. Choose the blue Create API button. Your settings should look like the accompanying screenshot.
    Create API page, showing API selections and settings.
    1. In the left navigation pane, select Resources under API: HelloWorldAPI.
    2. Ensure the "/" resource is selected.
    3. From the Actions dropdown menu, select Create Method.
    4. Select POST from the new dropdown that appears, then select the checkmark.
    5. Select Lambda Function for the Integration type.
    6. Select the Lambda Region you used when making the function (or else you will see a warning box reading "You do not have any Lambda Functions in...").
    7. Enter HelloWorldFunction in the Lambda Function field.
    8. Choose the blue Save button.
    9. You should see a message letting you know you are giving the API you are creating permission to call your Lambda function. Choose the OK button.
    10. With the newly created POST method selected, select Enable CORS from the Action dropdown menu.
    11. Leave the POST checkbox selected and choose the blue Enable CORS and replace existing CORS headers button.
    Enable CORS configuration page.

    10. You should see a message asking you to confirm method changes. Choose the blue Yes, replace existing values button.

    Confirm method changes message.
    1. In the Actions dropdown list, select Deploy API.
    2. Select [New Stage] in the Deployment stage dropdown list.
    3. Enter dev for the Stage Name.
    4. Choose Deploy.
    5. Copy and save the URL next to Invoke URL (you will need it in module five).
    1. In the left navigation pane, select Resources.
    2. The methods for our API will now be listed on the right. Choose POST.
    3. Choose the small blue lightning bolt.
    4. Paste the following into the Request Body field:

    5. Choose the blue Test button.

    6. On the right side, you should see a response with Code 200.

    7. Great! We have built and tested an API that calls our Lambda function.

Application architecture

Module three is now complete. Time to review our architecture:

Architecture diagram showing services hosted in AWS Cloud, with connections shown from external users to interconnected AWS services.

We added API Gateway and connected it to our existing Lambda function. Now, we can trigger our function with an API call. We are still missing the ability to generate this call from our web client. We will add our data table first in module four and connect everything together in module five.

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