Serverless REST API: AWS Lambda, API Gateway & DynamoDB

Why Serverless? Moving Beyond Always-On Provisioned Compute

In traditional infrastructure patterns—such as the EC2 instances provisioned in my Expense Tracker lab—virtual machines run 24 hours a day, 7 days a week, consuming compute budget regardless of whether incoming requests arrive. Managing VMs also imposes administrative friction: patching operating systems, handling SSH or SSM daemon connectivity, configuring reverse proxies like Nginx, and managing process managers.

For intermittent workloads, background webhooks, and lightweight CRUD microservices, an event-driven serverless architecture offers an alternative:

• Zero Idle Compute Costs: Compute execution billing only begins when an HTTP request arrives and terminates immediately after the response payload is returned.
• No Operating System Maintenance: The underlying runtime container environment, security patches, and hardware scaling are abstracted away by AWS.
• Elastic Concurrency: Invocations scale horizontally and automatically in response to request volume without pre-provisioning Auto Scaling Groups.

The objective of this project was to establish and verify an end-to-end serverless CRUD flow on AWS: deploying an HTTP API using Amazon API Gateway, proxying calls directly to an AWS Lambda function (gettodo), and storing state in Amazon DynamoDB (tasks table) with real-world verification through Hoppscotch and the AWS Management Console.

End-to-End Request Flow: API Gateway to DynamoDB

The architecture follows a classic serverless three-tier pattern in AWS ap-south-1. Every request flows through managed AWS services without a single long-running virtual machine:

+-----------------------+
|  HTTP Client          |
|  (Hoppscotch REST)    |
+-----------+-----------+
            |
            | 1. HTTPS POST /dev/tasks  {"title": "...", "status": "..."}
            |    HTTPS GET  /dev/tasks/{id}
            v
+-------------------------------------------------------------+
|  Amazon API Gateway (task-api · ID: sl0g7w7uli)             |
|  Region: ap-south-1 | Stage: dev                            |
|  - CORS Preflight (OPTIONS /tasks, OPTIONS /tasks/{id})     |
|  - Resource Tree: /tasks (GET, POST), /tasks/{id} (GET)     |
|  - AWS_PROXY Integration (Pass-through event mapping)       |
+-----------------------------+-------------------------------+
                              |
                              | 2. Lambda Proxy Event
                              |    (body, pathParameters, headers)
                              v
+-------------------------------------------------------------+
|  AWS Lambda Function (gettodo)                              |
|  - Parses event JSON payload                                |
|  - Generates UUID v4 identifier for new tasks               |
|  - Executes PutItem / GetItem operations via AWS SDK        |
|  - Formats structured HTTP response (200 / 201)             |
+-----------------------------+-------------------------------+
                              |
                              | 3. DynamoDB SDK Read / Write
                              v
+-------------------------------------------------------------+
|  Amazon DynamoDB (Table: tasks)                             |
|  - Partition Key: id (String UUID)                          |
|  - Attributes: title (String), status (String)              |
|  - Consumed RCUs: 2 RCUs per item scan                      |
+-------------------------------------------------------------+

Verified Endpoints, Schemas & AWS Resources

All resource names, identifiers, and payload structures below correspond strictly to the actual AWS environment captured in the screen recording:

// Request Body:
{
  "title": "Learn AWS Lambda",
  "status": "pending"
}

// Response Body (201 Created):
{
  "id": "ba75fed5-9f42-4aa9-9f8a-165ab10d3600",
  "title": "Learn AWS Lambda",
  "status": "pending"
}

// Request Body:
{
  "title": "Learn AWS TF",
  "status": "done"
}

// Response Body (201 Created):
{
  "id": "2a54cc82-1faf-44d9-bacd-5ea316704f01",
  "title": "Learn AWS TF",
  "status": "done"
}

Authentic Screen Recording: Live End-to-End Verification

The video below demonstrates the full serverless flow in real time across the AWS Management Console and Hoppscotch API client:

Key Architectural Decisions & Observations

Implementation Status & Honest Technical Boundaries

What Building This Taught Me & Future Improvements