Client-server architecture is the backbone of modern networked applications. It's like a restaurant where clients (customers) order food, and servers (kitchen staff) prepare and deliver it. This setup allows for efficient resource sharing and scalable systems.

The client-server model involves two main players: clients that request services and servers that provide them. They communicate using protocols like HTTP, with servers listening on specific ports. This setup can be tweaked to handle different workloads and user needs.

Client-Server Basics

Fundamental Components and Models

• Client functions as the user-facing application or device requesting services or resources
• Server operates as a dedicated computer or program providing resources, services, or data to clients
• Request-response model forms the basis of client-server communication involves clients sending requests and servers responding with data or services
• Thin client relies heavily on the server for processing and data storage minimizes local resource usage (web browsers)
• Thick client performs significant processing locally reduces server load and enhances offline capabilities (desktop applications)

Communication Protocols and Interactions

• HTTP (Hypertext Transfer Protocol) facilitates communication between web clients and servers
• TCP/IP (Transmission Control Protocol/Internet Protocol) ensures reliable data transmission across networks
• Clients initiate connections to servers using specific port numbers (HTTP uses port 80, HTTPS uses port 443)
• Servers listen for incoming client requests on designated ports
• Multiple clients can simultaneously connect to a single server enabling concurrent service provision

Server Characteristics

Server Types and State Management

• Stateless servers treat each request independently maintain no information about previous client interactions
• Stateful servers preserve client session information between requests enable personalized experiences and transaction management
• Load balancing distributes incoming client requests across multiple servers improves performance, reliability, and fault tolerance
• Round-robin load balancing assigns requests to servers in a circular sequence
• Least connections load balancing directs requests to servers with the fewest active connections

Scalability and Performance Optimization

• Vertical scaling involves increasing the resources (CPU, RAM, storage) of individual servers
• Horizontal scaling adds more servers to the system distributes the workload across multiple machines
• Caching mechanisms store frequently accessed data in memory reduce database queries and improve response times
• Content Delivery Networks (CDNs) distribute server content across geographically dispersed locations minimize latency for users in different regions
• Database sharding partitions data across multiple servers improves query performance and enables handling of large datasets

Architecture

Three-tier Architecture Components

• Presentation tier handles user interface and client-side logic (web browsers, mobile apps)
• Application tier processes business logic, applies rules, and manages data flow between presentation and data tiers
• Data tier stores and retrieves data typically implemented using databases (MySQL, PostgreSQL, MongoDB)

Three-tier Architecture Benefits and Implementation

• Separation of concerns enhances modularity and maintainability allows independent development and scaling of each tier
• Improved security isolates sensitive data in the data tier from direct client access
• Scalability enables independent scaling of each tier based on specific performance requirements
• Load balancing can be applied at multiple levels (presentation tier, application tier) for optimal resource utilization
• Microservices architecture extends the three-tier model by further decomposing the application tier into smaller, independent services