# Guided scenarios to build real intuition for distributed systems.

## Beginner

### [URL Shortener] (https://cascode.uk/canvas/?challenge=url-shortener)  
Design a URL shortener that handles 10,000 read requests per second with sub-10ms latency.  
*Technologies: API Gateway, Lambda, DynamoDB, ElastiCache*

### [Order Notification Pipeline] (https://cascode.uk/canvas/?challenge=order-notifications)  
When a customer places an order, send an email AND update inventory — reliably, even if one service is down.  
*Technologies: API Gateway, SNS, SQS, Lambda*

### [Async Image Processor] (https://cascode.uk/canvas/?challenge=image-processing)  
Users upload images to S3. A pipeline resizes them to 3 sizes without blocking the upload response.  
*Technologies: S3, SQS, Lambda*

### [Event-Driven Inventory Sync] (https://cascode.uk/canvas/?challenge=inventory-sync)  
A warehouse uploads a CSV to S3 every hour. Three downstream systems (pricing, search, analytics) each need the changes — at their own pace, without blocking each other.  
*Technologies: S3, SNS, SQS, Lambda, DynamoDB*

## Intermediate

### [Fraud Detection System] (https://cascode.uk/canvas/?challenge=fraud-detection)  
Flag suspicious orders in real time without blocking the checkout flow. High traffic: 500 orders/s at peak.  
*Technologies: API Gateway, Lambda, SQS, Step Functions, DynamoDB*

### [Real-Time Leaderboard] (https://cascode.uk/canvas/?challenge=leaderboard)  
A gaming leaderboard that serves 50,000 reads/s but only ~100 writes/s. Cost must be minimised.  
*Technologies: API Gateway, Lambda, ElastiCache, DynamoDB*

### [E-Commerce Checkout] (https://cascode.uk/canvas/?challenge=checkout-with-rds)  
Your checkout service hammers RDS with Lambda connections and crashes on Black Friday. Fix it without touching the schema.  
*Technologies: API Gateway, Lambda, RDS, ElastiCache, SQS*

### [Auto-Scaling Web Tier] (https://cascode.uk/canvas/?challenge=autoscaling-web-tier)  
A traditional web app on EC2 fails under 10× traffic spikes. Redesign it to scale automatically without over-provisioning.  
*Technologies: API Gateway, EC2, RDS, ElastiCache, S3*

## Advanced

### [Multi-Region Disaster Recovery] (https://cascode.uk/canvas/?challenge=multi-region-dr)  
A region-wide AWS outage would take your API completely offline. Design for RTO < 1 min and RPO < 5 seconds.  
*Technologies: API Gateway, Lambda, DynamoDB, S3, SNS*

### [Cost-Optimised Data Pipeline] (https://cascode.uk/canvas/?challenge=data-pipeline-cost)  
Your nightly pipeline processes 50 GB of events and costs $800/month. Cut it to under $200 using the right AWS options — without changing the output.  
*Technologies: S3, SQS, Lambda, DynamoDB, Step Functions*