System design interview basics, visualized
System design interviews test a small set of building blocks combined under constraints. Learn each block by watching requests flow through it, then practise combining them on the study guides below.
Start with the interview methodology and the client-server model; the networking and scaling topics after them are what every design answer is made of.
Start here
Beginner topics, in the order they build on each other.
- System Design Interview MethodologyThe framework every system design interview actually follows — clarify requirements, estimate scale, define the API, sketch the high-level design, deep-dive on what the interviewer steers toward, and discuss tradeoffs — taught explicitly as its own transferable skill, worked through against a running example.Beginner20m
- Client-Server ModelAnimate the end-to-end data flow from client through the web and application tiers down to the database.Beginner10m
- OSI Model LayersAnimate data encapsulation and decapsulation as it travels through the 7 layers of the OSI model.Beginner20m
- TCP 3-Way HandshakeAnimate the standard Transmission Control Protocol handshake to understand connection reliability.Beginner10m
- Access Control StrategiesVisualize the difference between Whitelisting (Default Deny) and Blacklisting (Default Allow) access models.Beginner10m
- Git & Version Control InternalsExplore Git as a directed commit graph, the staging area, rebase vs. merge, undoing changes, remote synchronization, and the underlying object model — six interactive scenes covering the Git concepts you use every day.Beginner30m
- Testing Strategy: The Test PyramidUnderstand how unit, integration, and end-to-end tests differ in speed, cost, and scope — and why the right balance matters for sustainable software delivery.Beginner13m
Next
Intermediate topics.
- DNS Resolution & CachingVisualize the hierarchical Domain Name System and how local caching speeds up internet browsing.Intermediate15m
- Network Address TranslationVisualize how NAT routers allow entire private networks to share a single public IP address.Intermediate15m
- VPC & SubnetsAnimate traffic flowing through an Internet Gateway into Public and Private subnets within a Virtual Private Cloud.Intermediate15m
- Load BalancerVisualize how load balancers distribute incoming requests across multiple servers using round-robin, least-connections, and weighted strategies.Intermediate15m
- Forward vs Reverse ProxyDemonstrate the difference between Forward and Reverse proxies and how they route network traffic.Intermediate10m
- API GatewayVisualize the role of an API Gateway in handling routing, authentication, and rate limiting for microservices.Intermediate15m
- Rate LimiterAnimate token bucket and sliding window rate limiting algorithms to understand API throttling and traffic control.Intermediate15m
- Caching StrategiesExplore LRU cache eviction, write-through, and write-back caching patterns with visual animations.Intermediate20m
- OAuth, OIDC & JWTUnderstand the complete authentication and authorization flow using OAuth 2.0, OpenID Connect (OIDC), and JSON Web Tokens (JWT) with interactive diagrams.Intermediate25m
- Message QueueVisualize pub/sub and point-to-point messaging patterns with animated producers, queue, and consumers.Intermediate15m
- Real-Time ProtocolsCompare Short Polling, Long Polling, Server-Sent Events (SSE), and WebSockets in a side-by-side race.Intermediate15m
- Perimeter SecurityExplore how Firewalls, DMZs, VPNs, and SSH secure the boundary between a private network and the internet.Intermediate15m
- Design Patterns & SOLID PrinciplesMaster the five SOLID principles and six classic Gang-of-Four design patterns with interactive before/after code examples and a reference gallery.Intermediate16m
- Concurrency & Threading ModelsVisualise race conditions, mutex locking, and the difference between concurrency and parallelism through an animated shared-account withdrawal demo.Intermediate15m
- Microservices vs MonolithCompare monolithic and microservices architectures through interactive deployment and failure simulations, learning when each pattern is the right tool for the job.Intermediate14m
- Containers & OrchestrationVisualize how containers differ from VMs, then watch an orchestrator schedule replicas and self-heal when a node fails.Intermediate15m
- Circuit Breakers & Resilience PatternsSimulate the three-state circuit breaker pattern and learn how it prevents cascading failures when a downstream service becomes unhealthy.Intermediate14m
- Observability: Logs, Metrics & TracesExplore the three pillars of observability — logs, metrics, and traces — by simulating a checkout request flowing through a three-service distributed system.Intermediate15m
- Kafka Consumer LagProduction Kafka health: tune produce and consume rates and watch consumer lag (log-end-offset minus committed offset) grow, spike, and drain — the metric you alert on in production.Intermediate18m
Advanced
For when the rest feels solid.
- CIDR SubnettingAn interactive calculator that demonstrates how Classless Inter-Domain Routing breaks IP spaces into subnets.Advanced20m
- Bloom FiltersInteractive visualizer for the Bloom Filter, a space-efficient probabilistic data structure used to save expensive disk reads.Advanced15m
- Kafka ArchitectureExplore the high-throughput, distributed event streaming architecture of Apache Kafka.Advanced20m
- Consistent HashingUnderstand how distributed caches handle scaling without massive data remapping using a hash ring.Advanced20m
- Leader Election (Raft)Visualize how distributed databases elect a Leader and recover from crashes using the Raft Consensus Algorithm.Advanced20m
- Gossip ProtocolVisualize how decentralized, leaderless clusters synchronize state exponentially fast using peer-to-peer epidemic protocols.Advanced15m
- Distributed Transactions (Saga vs 2PC)Learn how microservices maintain data consistency across multiple databases using Two-Phase Commit and Saga patterns.Advanced20m
- Network IsolationUnderstand VLANs, Security Groups, and Software-Defined Networking (SDN).Advanced20m
- Kafka Replication & Leader ElectionProduction Kafka fault tolerance: replicate a partition across brokers, commit with acks=all, and watch the controller elect a new leader from the ISR when a broker crashes.Advanced22m
- Kafka Consumer Group RebalancingProduction Kafka scaling: watch a topic’s partitions get reassigned across a consumer group as consumers join and leave, under the Range and RoundRobin assignors.Advanced20m
Design walkthroughs
Interview-style study guides: requirements, estimates, API, data model and trade-offs. They open in the System Designer, which needs a desktop-width screen.