System Design

The interview round that decides senior offers — and the thinking that makes real systems survive.

1. Step 01

   Building blocks

   Load balancers, caches, CDNs, queues, object storage and how each fails.

   Architecture

2. Step 02

   Data layer

   SQL vs NoSQL choices, indexing, replication, sharding and consistency models.

   DatabasesCAP

3. Step 03

   Scaling patterns

   Read replicas, fan-out, rate limiting, backpressure and idempotency.

   Scalability

4. Step 04

   Reliability

   Redundancy, timeouts, retries, circuit breakers, graceful degradation and DR.

   Resilience

5. Step 05

   Case studies

   URL shortener, news feed, chat, ride matching, payment ledger, notification service.

   Case Studies

6. Step 06

   Communication

   Requirement clarification, capacity estimates, diagramming and defending trade-offs aloud.

   EstimationTrade-offs