Serverless Data Retrieval using AWS Lambda and API Gateway

1. Create an S3 Bucket:

• Sign in to the AWS Management Console and open the Amazon S3 console at https://console.aws.amazon.com/s3/.
• On the S3 page, click on the "Create bucket" button.
• Provide a unique name for the bucket, select a region, and leave the other settings as default.
• Click "Create bucket" to complete the process.
• This bucket will be used to store your JSON data.

2. Upload JSON Data:

• After you have created the S3 bucket, click on the bucket to open it.
• Then, click on the "Upload" button.
• Select the JSON file you want to upload.
• Click on the “Upload” button at the bottom to start the upload.
  
• Once the file is uploaded you will see a success screen. Press the “Close” button at the top right
• You can now see the JSON file in your S3 bucket.

3. Create a Lambda Function:

• Open the Lambda console

• On the Lambda page, click on the "Create function" button.

• Select the "Author from scratch" option.

• Give your function a name (eg. GetTodos), select a runtime (e.g. Python)

• Expand the Change Default Execution dropdown, Select Create a new role from AWS policy templates, Assign a role name (eg. GetTodosLambdaRole) and from the policy templates select (search for) Amazon S3 object read-only permissions.

• Click on Create Function
  

• This function will be used to retrieve the JSON data from the S3 bucket and return it to the API endpoint.

4. Add Code to the Lambda Function:

• In the Lambda function editor, scroll to the bottom where you will find a code window with a file with a name like lambda_function.py open
• paste the following code, which will retrieve the JSON data from the S3 bucket:

import boto3
import json

def lambda_handler(event, context):
    s3 = boto3.client("s3")
    bucket = "your-bucket-name"
    key = "your-json-file-name.json"
    response = s3.get_object(Bucket=bucket, Key=key)
    json_data = response["Body"].read().decode("utf-8")
    json_content = json.loads(json_data)
    
    return {
        'statusCode': 200,
        'body': json_content
    }

• Replace "your-bucket-name" with the actual name of your S3 bucket and "your-json-file-name.json" with the actual name of the JSON file you uploaded.
• Save the changes by clicking on the “File” → "Save" button.
• Finally, click on “Deploy”

4. Test the Lambda Function:

• Click on the Test button,

• give a name to the test event (e.g. MyTestEvent), leave others setting as default and save the test event

• Click on the Test button again, and select the event you just created.

• The result will be shown in the execution tab, near your code window. If the status says succeeded, your lambda function works as expected.

  

5. Create an API Gateway:

• Sign in to the API Gateway console
• If this is your first time using API Gateway, you see a page that introduces you to the features of the service. Under REST API, choose Build. When the Create Example API popup appears, choose OK.
• If this is not your first time using API Gateway, choose Create API. Under REST API, choose Build.
• Create an empty API as follows:
  • Under Create new API, choose New API.
  • Under Settings:
    • Enter the API name, If desired, enter a description in the Description field; otherwise, leave it empty.
    • Leave Endpoint Type set to Regional.
  • Choose Create API.
    

6. Create a Resource:

• Choose the root resource (/) in the Resources tree.
• Choose Create Resource from the Actions dropdown menu.
• Leave Configure as proxy resource unchecked.
• Set **Resource Name (**eg get-todo) and Resource Path (eg /get-todo)
• Leave Enable API Gateway CORS unchecked.
• Click on Create Resource

7. Create A method:

• In the Resources list, choose the resource you just created (eg /get-todo)

• In the Actions menu, choose Create method.

• Choose GET from the dropdown menu, and choose the checkmark icon

  

• Leave the Integration type set to Lambda Function.

• Choose Use Lambda Proxy integration.

• From the Lambda Region dropdown menu, choose the region where you created the Lambda function.

• In the Lambda Function field, type any character and choose from the dropdown menu.

• Leave Use Default Timeout checked.

• Choose Save.

• Choose OK when prompted with Add Permission to Lambda Function.

8. Deploy the API:

• After you have created the resource and method, you'll need to deploy the API.
• Click on the "Actions" menu, and then select "Deploy API".
• Choose a deployment stage (e.g. "prod"), and then click on the "Deploy" button.
• You'll now see the "Invoke URL" for your API, which you can use to access the JSON data.

9. Test the API:

• Open a web browser, and paste the "Invoke URL" + “ResourceName” for your API into the address bar.
  • Eg: If Invoke URL is https://d0sqmtu4yg.execute-api.us-east-1.amazonaws.com/prod and Resource name is /get-todo, paste [https://d0sqmtu4yg.execute-api.us-east-1.amazonaws.com/pro](https://d0sqmtu4yg.execute-api.us-east-1.amazonaws.com/prod)d/get-todo
• You should see the JSON response similar to what we saw during the lambda testing