System Design Interview Prep — HLD & LLD Guide | Interview Prep Buddy
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Master High-Level Design (HLD) and Low-Level Design (LLD) from single-server monoliths to global-scale distributed systems handling billions of users.

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Architectural Case Studies

✅ 0 / 30 completed🏆 0 XP

Step-by-step scaling patterns from real-world products.

Showing 30 of 30 case studies — numbered badges below mark the curated 1-12 starter path

1⚡ InteractiveEasy

Design URL Shortener (TinyURL)

Key generation, redirection, caching, and database scaling.

Real-world parallel: Google, Bitly

2⚡ InteractiveEasy

Design a Rate Limiter

Token bucket in Redis for fair, distributed API request limiting.

Real-world parallel: Cloudflare, Stripe

3⚡ InteractiveMedium

Design a Distributed Cache

Consistent hashing, replication, and failover like Redis or Memcached.

Real-world parallel: Redis, Meta

4⚡ InteractiveMedium

Design Chat App (WhatsApp)

WebSocket servers, message queuing, delivery status checks, and presence store.

Real-world parallel: Meta, WhatsApp

5⚡ InteractiveMedium

Design a News Feed (Twitter/Instagram)

Fan-out write/read paths, feed caching, media storage, and scaling read paths.

Real-world parallel: Meta, Twitter/X

6⚡ InteractiveMedium

Design a Web Crawler

Frontier, politeness, deduplication, and storage at Googlebot scale.

Real-world parallel: Google

7⚡ InteractiveMedium

Design a Proximity Service (Yelp)

Geohashing and quadtrees for fast nearby-places search at scale.

Real-world parallel: Yelp, Google Maps

8⚡ InteractiveMedium

Design a Ticket Booking System (BookMyShow)

Seat-hold locking to prevent double-booking and flash-sale traffic spikes.

Real-world parallel: BookMyShow, Ticketmaster

9⚡ InteractiveHard

Design a Distributed Key-Value Store (DynamoDB)

Quorum reads/writes, vector clocks, hinted handoff, and LSM-trees.

Real-world parallel: Amazon DynamoDB

10⚡ InteractiveHard

Design a Distributed Lock Service

Leases, fencing tokens, and consensus-backed mutual exclusion.

Real-world parallel: ZooKeeper, Google Chubby

11⚡ InteractiveHard

Design a Payment System

Idempotent transactions, reconciliation loops, and ledger architecture.

Real-world parallel: Stripe, PayPal

12⚡ InteractiveHard

Design a Collaborative Editor (Google Docs)

Operational Transformation, CRDTs, and live multi-user presence.

Real-world parallel: Google Docs, Figma

⚡ InteractiveMedium

Design a Distributed Job Scheduler

Leader election, exactly-once triggers, and DAG dependencies.

Real-world parallel: Airbnb, LinkedIn

⚡ InteractiveMedium

Design a Notification System

Batching, delivery, and multi-channel (push, email, SMS) fan-out.

Real-world parallel: Amazon, Uber

Medium

Design an API Gateway

Routing, auth, request aggregation, and per-dependency circuit breaking.

Real-world parallel: Netflix, Kong

Medium

Design Instagram

Async image processing pipeline, TTL-based ephemeral Stories, and embedding-based discovery feed.

Real-world parallel: Instagram, Meta

⚡ InteractiveMedium

Design Search Autocomplete

Real-time typeahead suggestions like Google Search autocomplete.

Real-world parallel: Google, Amazon

Hard

Design a Distributed Search Engine

Sharded inverted index, scatter-gather queries, and BM25 relevance ranking.

Real-world parallel: Elastic, Google

⚡ InteractiveHard

Design an Ad Click Aggregation System

Streaming aggregation, HyperLogLog counting, and fraud dedup.

Real-world parallel: Google Ads, Meta Ads

⚡ InteractiveHard

Design an E-commerce Order System (Amazon)

Inventory reservation, order state machine, and saga-coordinated checkout.

Real-world parallel: Amazon, Walmart

⚡ InteractiveHard

Design Cloud Storage (Google Drive)

Chunking uploads, sync conflict resolution, and metadata sharding.

Real-world parallel: Dropbox, Google

⚡ InteractiveHard

Design Distributed Message Queue (Kafka)

Partitioned commit logs, consumer groups, OS zero-copy (sendfile), and ISR replicas.

Real-world parallel: LinkedIn, Confluent

⚡ InteractiveHard

Design Metrics & Monitoring System (Prometheus)

Pull metrics scraper, Gorilla XOR TSDB compression, and rollup downsampling.

Real-world parallel: Datadog, Prometheus

⚡ InteractiveHard

Design Property & Hotel Booking (Airbnb)

365-day availability bitmaps, 15-min SETNX reservation holds, and Quadtree search.

Real-world parallel: Airbnb, Booking.com

⚡ InteractiveHard

Design Real-Time Chat & Voice (Discord/Slack)

Elixir WS gateway, ScyllaDB channel logs, WebRTC SFUs, and presence aggregation.

Real-world parallel: Discord, Slack

⚡ InteractiveHard

Design Ride-Sharing (Uber)

Geospatial indexing (Geohash), WebSocket connections, and matching service.

Real-world parallel: Uber, Lyft

⚡ InteractiveHard

Design Short Video Platform (TikTok/Reels)

Parallel chunk uploads, HLS transcoding, recommendation feed ranker, and Flink analytics.

Real-world parallel: TikTok, ByteDance

Hard

Design Twitter/X

Retweet fan-out amplification and real-time trending topics via Count-Min Sketch.

Real-world parallel: Twitter/X

⚡ InteractiveHard

Design UPI

VPA resolution, switch-coordinated interbank debit/credit, and deferred net settlement.

Real-world parallel: NPCI, Google Pay, PhonePe

⚡ InteractiveHard

Design Video Streaming (YouTube/Netflix)

Transcoding pipelines, CDN delivery, view counters, and upload flow.

Real-world parallel: YouTube, Netflix

📚 HLD Fundamentals Course

Master the building blocks of distributed systems before diving into case studies.