🧩 Serverless To-Do App

🚀 A fully serverless CRUD API built with AWS Lambda, API Gateway, and DynamoDB.
Designed for beginners learning Python + AWS Cloud Integration.

🧩 Serverless To-Do Application (AWS Lambda + API Gateway + DynamoDB)

A fully serverless To-Do API built with AWS Lambda, API Gateway, and DynamoDB — designed for beginners learning AWS Cloud & Python integration.
This app supports Create, Read, Update, and Delete (CRUD) operations using a single Lambda function.

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⚙️ Features

• Single Lambda function handles all CRUD operations
• DynamoDB for To-Do storage
• API Gateway provides REST endpoints
• 100 % Serverless — no servers to manage
• Written in Python using boto3

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🧱 Architecture Diagram

                 ┌────────────────────────────┐
                 │     Client (Postman / UI)   │
                 └──────────────┬──────────────┘
                                │ HTTPS
                                ▼
                 ┌────────────────────────────┐
                 │     Amazon API Gateway      │
                 │  Routes: /todos , /todos/{id} │
                 └──────────────┬──────────────┘
                                │
                                ▼
                 ┌────────────────────────────┐
                 │     AWS Lambda (Python)     │
                 │  Single Function: CRUD Ops  │
                 └──────────────┬──────────────┘
                                │
                                ▼
                 ┌────────────────────────────┐
                 │     Amazon DynamoDB Table   │
                 │  Table: TodoTable (id: str) │
                 └────────────────────────────┘

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🪣 AWS Console Setup (Recommended)

Step 1 – Create DynamoDB Table

1. Go to AWS Console → DynamoDB → Tables → Create table
2. Table name → TodoTable
3. Partition key → id (String)
4. Leave defaults → Create Table

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Step 2 – Create Lambda Function

1. Go to AWS Console → Lambda → Create function
2. Choose Author from scratch
3. Function name → ServerlessToDoFunction
4. Runtime → Python 3.9 or later
5. Permissions → Attach AmazonDynamoDBFullAccess
6. Click Create Function
7. Paste your lambda_function.py code in the editor
8. Click Deploy

🧩 This one function handles all 4 methods (POST, GET, PUT, DELETE)

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Step 3 – Create API Gateway

1. API Gateway → Create API → HTTP API → Build
2. Name → ToDoAPI
3. Create these routes:

Method	Path	Description
POST	/todos	Create To-Do
GET	/todos	Get all To-Dos
PUT	/todos/{id}	Update To-Do
DELETE	/todos/{id}	Delete To-Do

4. For each route, choose:
   • Integration type → Lambda
   • Function → ServerlessToDoFunction
5. Deploy the API → Create a stage called prod
6. Copy your Invoke URL — example:

   https://abc123.execute-api.ap-south-1.amazonaws.com/prod
   

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Step 4 – Test with Postman

Operation	Method	Endpoint	Body Example
Create	POST	/todos	{ "task": "Learn AWS Lambda" }
Read	GET	/todos	—
Update	PUT	/todos/{id}	{ "status": "completed" }
Delete	DELETE	/todos/{id}	—

Example URL:

https://abc123.execute-api.ap-south-1.amazonaws.com/prod/todos

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💻 Local Setup (For VS Code Users)

If you prefer to test or modify the API locally before deploying to AWS:

1. Create and activate a virtual environment

python -m venv venv
venv\Scripts\activate   # On Windows
source venv/bin/activate  # On Mac/Linux

2. Install Dependencies

pip install -r requirements.txt

3. Set AWS credentials

aws configure

4. Run the script locally

python lambda_function.py

5. Test locally using Postman or curl

curl -X POST http://localhost:8000/todos -H "Content-Type: application/json" -d '{"task": "Test local To-Do", "status": "pending"}'

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📦 Example Inputs and Outputs

➕ Create To-Do (POST)

Input

{
  "task": "Complete AWS Serverless To-Do App",
  "status": "pending"
}

Output

{
  "message": "ToDo created",
  "item": {
    "id": "e43664c5-6ebc-4d28-987a-cc2c99b5fdee",
    "task": "Complete AWS Serverless To-Do App",
    "status": "pending",
    "created_at": "2025-11-03T10:51:40.727920"
  }
}

📋 Get All To-Dos (GET)

Output

[
  {
    "id": "e43664c5-6ebc-4d28-987a-cc2c99b5fdee",
    "task": "Complete AWS Serverless To-Do App",
    "status": "pending",
    "created_at": "2025-11-03T10:51:40.727920"
  }
]

✏️ Update To-Do (PUT)

Input

{
  "status": "completed"
}

Output

{
  "message": "ToDo updated",
  "item": {
    "id": "e43664c5-6ebc-4d28-987a-cc2c99b5fdee",
    "task": "Complete AWS Serverless To-Do App",
    "status": "completed",
    "created_at": "2025-11-03T10:51:40.727920"
  }
}

❌ Delete To-Do (DELETE)

Output

{
  "message": "ToDo deleted successfully",
  "deleted_id": "e43664c5-6ebc-4d28-987a-cc2c99b5fdee"
}

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🧩 How to Run This Project Locally

This project’s Lambda function can be tested in two ways — connected to AWS or offline.

🟢 Option 1: AWS-Connected Local Test (Real DynamoDB)

If you have AWS CLI configured (aws configure), and a DynamoDB table named TodoTable, follow these steps:

python -m venv venv
venv\Scripts\activate
pip install -r requirements.txt
python lambda_function.py

You’ll see the simulated event result printed in your terminal.

Example output:

{
  "statusCode": 201,
  "body": "{\"message\": \"ToDo created\", \"item\": {\"id\": \"abc123\", \"task\": \"Learn AWS Serverless\", \"status\": \"pending\"}}"
}

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🔵 Option 2: Offline Mock Test (No AWS Required)

To test without AWS:

1. Open lambda_function.py
2. Add this code block before your DynamoDB initialization:

   class MockTable:
       def __init__(self):
           self.storage = {}
   
       def put_item(self, Item):
           self.storage[Item["id"]] = Item
   
       def scan(self):
           return {"Items": list(self.storage.values())}
   
       def update_item(self, Key, UpdateExpression=None, ExpressionAttributeNames=None, ExpressionAttributeValues=None, ReturnValues=None):
           item = self.storage.get(Key["id"])
           if not item:
               return {"Attributes": {}}
           if ":s" in ExpressionAttributeValues:
               item["status"] = ExpressionAttributeValues[":s"]
           if ":t" in ExpressionAttributeValues:
               item["task"] = ExpressionAttributeValues[":t"]
           self.storage[Key["id"]] = item
           return {"Attributes": item}
   
       def delete_item(self, Key):
           self.storage.pop(Key["id"], None)
   
   # Uncomment below line for offline testing
   # table = MockTable()

3. Comment out your DynamoDB line:

   # table = dynamodb.Table('TodoTable')

4. Run:

   python lambda_function.py

Example output:

{
  "statusCode": 201,
  "body": "{\"message\": \"ToDo created (mock)\", \"item\": {\"id\": \"1234\", \"task\": \"Test offline mode\", \"status\": \"pending\"}}"
}

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👨‍💻 Author

Avinash S
AWS Cloud Engineer | Python Developer
🌐 GitHub Profile