Goal: Understand distributed system tradeoffs (CAP, consistency, failover) and master the SOLID principles — the design vocabulary every interviewer expects you to speak fluently.
Topics
| Day | Focus | Topics |
|---|---|---|
| Mon | HLD Reliability | CAP Theorem · Consistency Models · Failover and Redundancy |
| Tue | HLD Communication | REST API Design · WebSockets · Polling, Long Polling, SSE |
| Wed | HLD Ops & Protection | Monitoring, Logging, Alerting · Rate Limiting |
| Thu | SOLID Principles (Part 1) | Single Responsibility Principle · Open/Closed Principle · Liskov Substitution Principle |
| Fri | SOLID Principles (Part 2) & DP | Interface Segregation Principle · Dependency Inversion Principle · 1D DP Patterns |
Key Concepts
- CAP theorem real-world examples — classify systems as CP (MongoDB, HBase) vs AP (Cassandra, DynamoDB)
- Strong vs eventual consistency — when each is acceptable and the spectrum in between
- Active-passive vs active-active failover — tradeoffs in cost, complexity, and recovery time
- REST best practices — idempotency, proper status codes (2xx/4xx/5xx), resource naming, HATEOAS
- WebSocket vs SSE vs polling — pick the right tool: bidirectional (WebSocket), server-push (SSE), simple (polling)
- Each SOLID principle with code violations and fixes — learn to spot and refactor anti-patterns
- SRP: one reason to change. OCP: extend without modifying. LSP: subtypes must be substitutable
- ISP: no client should depend on methods it doesn’t use. DIP: depend on abstractions, not concretions
- 1D DP patterns — climbing stairs, house robber, decode ways, coin change variations
Practice
- Classify 5 real databases as CP or AP and justify your reasoning
- Design a RESTful API for a bookstore — define resources, endpoints, status codes, and error responses
- Refactor a God class that handles user auth, email sending, and logging into SRP-compliant classes
- Solve the house robber problem using both top-down and bottom-up DP
~14 topics · ~1.5-2 hrs/day · Focus: read the linked notes, then code each concept