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Client-Server Architecture

Learn how clients and servers communicate over networks.

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Client-Server Model

The client-server model is the foundation of all web applications. A client sends requests, and a server processes them and sends back responses.

Client-Server Communication

    Client                    Server
  +--------+              +--------+
  | Browser | --Request--> | Web    |
  | App     | <--Response-- | Server |
  +--------+              +--------+
     |                         |
     |     HTTP/HTTPS          |
     +=========================+

Types of Clients

  1. Web Browser — Sends HTTP requests, renders HTML/CSS/JS
  2. Mobile App — Sends API requests (REST/GraphQL)
  3. CLI Tool — Sends requests from command line
  4. Service Client — Other backend services (microservices)

Types of Servers

  1. Web Server — Serves static files (Nginx, Apache)
  2. Application Server — Runs business logic (Tomcat, Spring Boot)
  3. Database Server — Stores and retrieves data (PostgreSQL, MySQL)
  4. Cache Server — Stores frequently accessed data (Redis)

The Request Lifecycle

1. Client constructs HTTP request
2. DNS resolves domain to IP address
3. TCP connection established
4. TLS handshake (for HTTPS)
5. Request sent to server
6. Server processes request
7. Server sends response
8. Client renders/processes response

Client-Server vs Peer-to-Peer

Feature Client-Server Peer-to-Peer
Structure Centralized Decentralized
Scalability Easier Harder
Security Easier to control Distributed trust
Use Case Web apps, APIs Blockchain, file sharing

Why This Matters for Backend

As a backend engineer, you are building the server side of this model. You need to:

  • Handle incoming requests efficiently
  • Process business logic correctly
  • Return appropriate responses
  • Handle errors gracefully
  • Scale to serve millions of clients

Architecture Patterns

Patterns

  • Layered: Traditional
  • Microservices: Distributed
  • Event-Driven: Async
  • Serverless: FaaS

Principles

  • Single Responsibility
  • loose coupling
  • High cohesion
  • Separation of concerns

Best Practices

  • Document decisions
  • Use ADRs
  • Consider trade-offs
  • Design for change

Key Points

  • Understanding Client-Server Architecture is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0/3solved
Implement Client-Server Architecture

Design and implement a solution for Client-Server Architecture in a backend system. Consider scalability, error handling, and production readiness.

Solution
// Client-Server Architecture implementation
// Key aspects: validation, error handling, logging, testing

public class ClientServerArchitecture {
    // Production-ready implementation
}
Client-Server Architecture Edge Cases

Identify and handle edge cases for Client-Server Architecture. What happens under high load, with invalid input, or during failures?

Solution
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
Client-Server Architecture Testing Strategy

Write a testing strategy for Client-Server Architecture. Include unit tests, integration tests, and performance tests.

Solution
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. In client-server architecture, where does business logic run?

Question 1 options

2. Which server type stores frequently accessed data?

Question 2 options

3. What is the primary purpose of Client-Server Architecture?

Question 3 options

4. What is a common mistake when implementing Client-Server Architecture?

Question 4 options

Flashcards

Question

What is client-server architecture?

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Answer

A model where clients send requests and servers process them

Question

Name 4 types of servers

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Answer

Web, Application, Database, Cache

Question

What is Client-Server Architecture?

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Answer

Client-Server Architecture is a key concept in backend development.

Question

When to use Client-Server Architecture?

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Answer

Use Client-Server Architecture when building production systems that require reliability, scalability, and maintainability.

Question

Client-Server Architecture best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1.Client sends requests, server processes and responds
  • 2.Multiple server types: web, application, database, cache
  • 3.The request lifecycle involves DNS, TCP, TLS, and HTTP

Interview Tips

  • •Be able to trace a request from browser to database
  • •Know the difference between web server and application server

Cheat Sheet

Client-Server

  • Client: Browser, mobile app, CLI, other services
  • Server: Web, Application, Database, Cache
  • Lifecycle: DNS -> TCP -> TLS -> HTTP Request -> Process -> Response