📝 Serverless To-Do List Web App (AWS Free Tier)

THis is a full-stack To-Do List Web App powered entirely by AWS Serverless Architecture — built to stay within the AWS Always Free Tier and designed to showcase practical, secure, and scalable cloud development.

🔗 Live Demo

👉 https://simple-to-do.pages.dev/home

🧰 Tech Stack

• Frontend: React, TypeScript, Vite, Cloudflare Pages

• Backend: AWS Lambda, Lambda Function URLs, DynamoDB, Cognito

• Reminders & Messaging: EventBridge Scheduler, SNS

• Monitoring & Security: CloudWatch, IAM Roles & Policies

  🚀 Features

• Sign up, log in, and manage personal to-dos

• Set email reminders for upcoming tasks

• Secure JWT-based authentication via AWS Cognito

• Built entirely using pay-as-you-go serverless services

• Frontend deployed on Cloudflare Pages

• Single-table DynamoDB design with flexible schema

• Real-time reminder scheduling via EventBridge

📸 Architecture Overview

🚀 Features

• Sign up, log in, and manage personal to-dos
• Set email reminders for upcoming tasks
• Built entirely with pay-as-you-go serverless services
• Deployed frontend via Cloudflare Pages

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🛠️ Core AWS Services & Their Roles

1. Amazon Cognito – User Management & Authentication

• Role: Handles sign-up, login, and JWT token issuance

• Key Configuration:

  • User Pool: Manages all users
  • App Client: Set as public client (no secret), ideal for SPAs

2. AWS Lambda – Serverless Backend Functions

• Role: Executes app logic (CRUD, reminders, notifications)

• Functions:

  • createTaskLambda, listTasksLambda, updateTaskLambda, deleteTaskLambda
  • setTaskReminderLambda, sendReminderNotificationLambda

3. Lambda Function URLs – Direct API Endpoints

• Role: Public HTTPS endpoints to invoke each Lambda
• Security: AuthType set to NONE; JWTs validated inside functions
• CORS: Configured for Cloudflare Pages & local development

4. Amazon DynamoDB – NoSQL Database

• Role: Stores users and tasks using a single-table design

• Schema:

  • PK: e.g., USER#<userId>
  • SK: e.g., TASK#<taskId>

• Flexible schema enables reminder attributes without altering structure

5. Amazon EventBridge Scheduler – Reminder Engine

• Role: Schedules one-time task reminders

• Workflow:

  • Triggers sendReminderNotificationLambda at specified time
  • Deletes itself after execution to stay within free tier limits

6. Amazon SNS – Email Notification Delivery

• Role: Sends reminder emails

• Workflow:

  • Lambda publishes reminder → SNS → Sends email to confirmed subscribers

7. Amazon CloudWatch – Logging & Monitoring

• Role: Collects logs from all Lambda functions for easy debugging

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🔐 IAM Roles & Policies

🔸 LambdaTodoAppRole (Worn by Lambda Functions)

• Permissions:

  • Full access to specific DynamoDB table
  • CloudWatch Logs access
  • EventBridge Scheduler management
  • SNS publishing

🔸 EventBridgeSchedulerToLambdaRole

• Used By: EventBridge
• Permission: Only invoke sendReminderNotificationLambda

🔸 Lambda Function URL Resource Policies

Each exposed function has a policy allowing public access via HTTPS:

{
  "Effect": "Allow",
  "Principal": "*",
  "Action": "lambda:InvokeFunctionUrl",
  "Condition": {
    "StringEquals": {
      "lambda:FunctionUrlAuthType": "NONE"
    }
  }
}

JWT-based auth is handled inside each function.

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🔁 How It Works

➕ Creating a Task with a Reminder

1. User logs in via React frontend (Cloudflare Pages)

2. Frontend sends JWT + task data to setTaskReminderLambda

3. Lambda:

   • Validates JWT
   • Updates DynamoDB with task & reminder
   • Creates a one-time EventBridge schedule

⏰ Sending Reminder Email

1. EventBridge fires at scheduled time
2. Triggers sendReminderNotificationLambda
3. Lambda publishes message to TaskRemindersTopic
4. SNS sends email to subscribed user

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🌐 Frontend

• Built with React + Vite
• Hosted on Cloudflare Pages
• Authenticates via AWS Cognito
• Communicates with Lambda URLs via HTTPS + JWTs

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💻 Local Development

1. Clone the repo and install frontend dependencies
2. Configure .env with AWS environment variables (Cognito IDs, Lambda URLs, etc.)
3. Use tools like Postman or browser for testing Function URLs

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