Realtime Serverless Voting App on AWS

A fully serverless, real-time voting application built with AWS CDK, Lambda, API Gateway (REST + WebSocket), DynamoDB, S3, and CloudFront (OAC).

Users can vote on a topic with 4 options and see results update instantly — no login required, no servers to manage.

This repository is the companion project for my Medium story explaining the full architecture and step-by-step implementation.

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Features

• Real-time voting with WebSocket updates
• Atomic counters with DynamoDB (safe under high concurrency)
• REST API for submitting votes
• WebSocket API for broadcasting results
• Static frontend hosted on S3 and delivered via CloudFront
• Secure private bucket with Origin Access Control (OAC)
• Infrastructure as Code with AWS CDK
• No authentication required (public voting)

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Architecture Overview

Browser
│
▼
CloudFront (HTTPS)
│
▼
Private S3 Bucket (OAC)
│
▼
Frontend (HTML + JS)
│
├── REST → API Gateway → Lambda → DynamoDB (atomic counters)
│
└── WebSocket → API Gateway → Lambda → DynamoDB (connections)
│
└── Broadcast results to clients

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Tech Stack

• AWS CDK (TypeScript)
• AWS Lambda (Node.js 18)
• API Gateway REST API
• API Gateway WebSocket API
• DynamoDB
• S3 Static Website Hosting
• CloudFront with Origin Access Control (OAC)
• Vanilla HTML + JavaScript frontend

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Project Structure

.
├── bin/
│ └── app.ts
├── lib/
│ └── realtime-voting-app-stack.ts
├── src/
│ ├── lambdas/
│ │ ├── vote.ts
│ │ ├── ws-connect.ts
│ │ └── ws-disconnect.ts
│ └── shared/
│ └── dynamo.ts
├── frontend/
│ ├── index.html
│ └── app.js
├── cdk.json
└── package.json

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Deployment

1. Prerequisites

• AWS account
• AWS CLI configured
• Node.js 18+

npm install -g aws-cdk

2. Install Dependencies

npm install

3. Bootstrap CDK (First Time Only)

cdk bootstrap

4. Deploy the Stack

cdk deploy

After deployment, CDK will output:

• REST API URL
• CloudFront Frontend URL

Open the Frontend URL in your browser to start voting.

Open it in multiple browsers or devices to see real-time updates.

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How Voting Works

1. User clicks a vote button
2. Browser sends REST request to /vote
3. Lambda increments DynamoDB atomic counter
4. Lambda broadcasts updated results to all WebSocket clients
5. Browsers update charts instantly

No polling. No refresh required.

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Security Notes

• S3 bucket is private
• Only CloudFront can access S3 using Origin Access Control (OAC)
• HTTPS enforced by CloudFront
• No public bucket access

This is production-grade static hosting.

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Ideas for Extension

If you want to evolve this project:

• Multiple topics / voting rooms
• Admin dashboard
• Vote reset and scheduling
• Rate limiting or CAPTCHA
• Authentication with Cognito
• DynamoDB Streams → Analytics pipeline

This architecture is a great base for any real-time public interaction system.

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Related Medium Story

This repository is built step-by-step in my Medium article:

Building a Real-Time Voting App with AWS CDK, API Gateway WebSocket, and DynamoDB