Building Blocks

Fundamental components used in almost every large-scale system. Each building block is a standalone deep dive with architecture, trade-offs, and real-world examples.

Index

Building Block	Description	When to Use
Load Balancers	Distribute traffic across multiple servers	Multiple app instances, high availability
Reverse Proxy	Single entry point; SSL termination, routing, caching	Fronting app servers, API gateway
CDN	Edge caching for static/dynamic content	Low-latency global delivery
Caching Layer	In-memory cache (e.g. Redis) for hot data	Read-heavy, latency-sensitive
Message Brokers	Queues and pub/sub for async processing	Decoupling, async jobs, events
Service Discovery	Find service instances in a dynamic cluster	Microservices, containers
API Gateway	Single entry for APIs; auth, rate limit, routing	Microservices, B2B APIs
Distributed Locks	Coordinate exclusive access across nodes	Leader election, critical sections
Rate Limiting	Limit requests per user/IP/key	Abuse prevention, fairness, cost control
Sharding	Partition data across multiple databases	Write scale, storage scale
Replication	Copy data across nodes for availability and read scale	HA, read scaling

How to Use

• Interview prep: Read each doc for concept overview, trade-offs, and real-world examples.

• Quick revision: Use the "Quick Revision" section at the end of each doc.

• Design discussions: Reference "When to use / When not to use" and "Failure scenarios."

Related

• Core concepts: core-concepts/ — Databases, caching, networking.

• Advanced: advanced-topics/ — Distributed systems, consistency, transactions.

• Case studies: hld-problems/ — URL shortener, cache, messaging, etc.