Building a REST API with AWS Gateway and Python
Tags: rest, aws, python, tutorial
Published: 2023-02-17 22:26:47

AWS Gateway is a powerful tool for building APIs that scale to meet the demands of modern web and mobile applications. With AWS Gateway, you can create RESTful APIs that expose your data and business logic to developers who can then build rich, interactive applications that consume your API.

REST API is an industry standard for building scalable, distributed web applications. With AWS Gateway, you can easily build a REST API that supports both GET and POST methods, as well as complex query parameters. You can also add support for other HTTP methods, such as PUT, DELETE, and HEAD.

Using AWS Gateway, you can quickly create APIs that are secure and robust. You can also use it to deploy your code to a production environment with minimal effort. Additionally, AWS Gateway allows for seamless integration with other AWS services, such as S3 and DynamoDB, enabling you to easily add complex functionality to your APIs.

## Prerequisites
Before building a RESTful API with AWS Gateway, you should have the following in place:

- [Create an AWS account](https://portal.aws.amazon.com/billing/signup?nc2=h_ct&src=header_signup&redirect_url=https%3A%2F%2Faws.amazon.com%2Fregistration-confirmation#/start/email) if you don’t have one already.
- Log in to the AWS Management Console and navigate to the Amazon API Gateway service.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/bj9sox7nrl7foho1scpo.png)

- Click on “Create API” and select “REST API”.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/31okfo4pkjaefyzdka0p.png)

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ejm6t0uqyc1skh8g210s.png)

- Click on “Actions” and define the resource and click “Create Resource”.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/pli6seqzowyl3bhhm10t.png)

- Select the newly created resource and click on “Create Method”.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/s1taq5kv2x7zimvrd81u.png)

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/eqxu03zkj3jhs0gg0t6c.png)

- Choose the HTTP verb (e.g. GET, POST, PUT, etc.) and click on the checkmark to create the method.

- In the “Integration type” section, select “Lambda Function” and enter the name of the Lambda function you want to use to handle the API requests.

- Click on “Save” to create the API.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/v0kaj8l5uqf8yldmmohh.png)

-Select Node from the Runtime Dropdown.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/gztv8f4fsg3xcpzl945r.png)

## Code Example
`import json
# Example data

data = {
    "items": [
        {"id": 1, "name": "Item 1", "price": 10.99},
        {"id": 2, "name": "Item 2", "price": 15.99},
        {"id": 3, "name": "Item 3", "price": 20.99},
    ]
}

def lambda_handler(event, context):
    # Determine the HTTP method of the request
    http_method = event["httpMethod"]
    # Handle GET request
    if http_method == "GET":
        # Return the data in the response
        response = {
            "statusCode": 200,
            "body": json.dumps(data)
        }
        return response

    # Handle POST request
    elif http_method == "POST":
        # Retrieve the request's body and parse it as JSON
        body = json.loads(event["body"])
        # Add the received data to the example data
        data["items"].append(body)
        # Return the updated data in the response
        response = {
            "statusCode": 200,
            "body": json.dumps(data)
        }
        return response

    # Handle PUT request
    elif http_method == "PUT":
        # Retrieve the request's body and parse it as JSON
        body = json.loads(event["body"])
        # Update the example data with the received data
        for item in data["items"]:
            if item["id"] == body["id"]:
                item.update(body)
                break
        # Return the updated data in the response
        response = {
            "statusCode": 200,
            "body": json.dumps(data)
        }
        return response

         # Handle DELETE request
    elif http_method == "DELETE":
        # Retrieve the request's body and parse it as JSON
        body = json.loads(event["body"])
        # Find the item with the specified id in the example data
        for i, item in enumerate(data["items"]):
            if item["id"] == body["id"]:
                # Remove the item from the example data
                del data["items"][i]
                break
        # Return the updated data in the response
        response = {
            "statusCode": 200,
            "body": json.dumps(data)
        }
        return response

    else:
        # Return an error message for unsupported methods
        response = {
            "statusCode": 405,
            "body": json.dumps({"error": "Method not allowed"})
        }
        return response`

This code defines a Lambda function, lambda_handler, that handles different types of HTTP requests (GET, POST, PUT, DELETE) on some data. The data is an object containing an array of items, each item has an id, name, and price.

When the function is called, it first determines the HTTP method of the request from the event object. Then it handles the request accordingly:
- GET: returns the data in the response with a status code of 200.
- POST: retrieves the request’s body and parse it as JSON, then add the received data to the example data, then returns the updated data in the response with a status code of 200.
- PUT: retrieves the request’s body and parse it as JSON, then update the example data with the received data, then returns the updated data in the response with a status code of 200.
- DELETE: retrieves the request’s body and parse it as JSON, then find the item with the specified id in the example data and remove it, then returns the updated data in the response with a status code of 200.
- If the method is not supported, it will return an error message with a status code of 405.

Deploy the API by clicking on “Actions” and selecting “Deploy API”.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/nvhnz58iz9ev3849l7bm.png)

Select a deployment stage (e.g. “prod” or “test”) and click on “Deploy”. Use the generated API endpoint to make requests to your API.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/a4a22jvtlpmqv497yike.png)

## Running and Testing The Code in Postman

Now, our API is up and running. You can send a test HTTP request through Postman. By sending a request to your invoke URL, you should see a 200 OK status code. For this test, no request body is needed for the incoming request.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/jgtj8ywgp68gm8pb6jcy.png)

## Wrapping Up

With that, we’ve created a simple RESTful API using AWS Lambda and Python. This code can serve as a foundation for creating more complex APIs for your application. As you continue to develop the API, you may want to consider implementing security measures such as an API key, integrating with an API gateway, [monitoring the usage of the API](https://www.moesif.com/features/api-analytics?utm_campaign=DevTo&utm_source=placed-article&utm_medium=body-cta&utm_content=build-rest-api-aws), or generating revenue through [API monetization](https://www.moesif.com/solutions/metered-api-billing?utm_campaign=DevTo&utm_source=placed-article&utm_medium=body-cta&utm_content=build-rest-api-aws). If you are interested in exploring options for API analytics and monetization check out [Moesif](https://www.moesif.com/wrap?onboard=true&utm_campaign=DevTo&utm_source=placed-article&utm_medium=body-cta&utm_content=build-rest-api-aws).