Retail & E-CommerceCloud Architecture

10K concurrent users, zero Black Friday incidents

IndustryE-Commerce / Retail

Team6 engineers

Timeline10 weeks

The Challenge

A UK-based e-commerce retailer experienced checkout failures during a flash sale that hit 800 concurrent users — 10× their usual traffic. Their Node.js monolith on a single EC2 instance couldn't handle session state under load, resulting in lost carts, failed payments, and £180K in abandoned orders. With Black Friday 3 months away, they needed to guarantee 10,000 concurrent users with zero incidents.

The Solution

TECHTIMIZE re-architected the platform onto AWS ECS with auto-scaling, moved session state to Redis ElastiCache, and implemented CloudFront CDN for static assets and pre-rendered product pages. The checkout flow was extracted as an independent microservice with dedicated resources. Stripe webhook processing moved to an SQS queue with exponential backoff retries. k6 load tests validated 12,000 concurrent users before go-live.

Technology Stack

ReactNode.jsMongoDBRedisAWS CloudFrontStripeAWS ECSk6

Results

Peak Capacity

Concurrent users handled on Black Friday with no incidents

Page Load Time

Product page load time reduced from 4.2s to 1.3s via CloudFront

Black Friday Revenue

Revenue uplift vs. previous year attributed to zero checkout failures

Infrastructure Cost

Monthly AWS cost reduced via Reserved Instances and right-sizing

How We Delivered It

Load Testing & Bottleneck Analysis

Ran k6 load tests against production to identify exact failure points: session store saturation at 800 concurrent users.

Architecture Redesign

Designed ECS auto-scaling topology, Redis session layer, CloudFront CDN strategy, and SQS payment processing queue.

Checkout Microservice Extraction

Extracted checkout, cart, and payment processing into isolated ECS services with dedicated task definitions and auto-scaling.

Redis & CloudFront Implementation

Deployed ElastiCache Redis cluster for session state and configured CloudFront with S3 origins and custom cache policies.

Load Testing & Validation

Ran progressive k6 load tests from 1K to 12K concurrent users, resolving 3 bottlenecks discovered during testing.

Black Friday Monitoring

War room with real-time CloudWatch dashboards and PagerDuty alerts during the live Black Friday sale.

"Black Friday was our best ever — 9,847 concurrent users at peak, zero errors, and our operations team had the quietest Friday in company history. Worth every penny."
CTO
UK E-Commerce Retailer

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