System Design Concepts: A Comprehensive Guide to Modern Architectural Principles
Introduction
To master system design, a complete understanding of core architectural concepts is essential. Here is a comprehensive breakdown of key system design concepts required to build robust, efficient, and scalable distributed systems.
1. Domain Name System (DNS)
The Domain Name System (DNS) maps human-readable domain names (like `www.koushiksaha.dev`) to machine-readable IP addresses (like `192.0.2.1`). The DNS lookup process goes through several layers: - **Recursive Resolver**: The initial server that receives the client request. - **Root Server**: Directs the resolver to the appropriate Top-Level Domain (TLD) server (e.g., `.dev`). - **TLD Server**: Provides the location of the Authoritative Name Server for the domain. - **Authoritative Name Server**: Returns the final target IP address to the client browser.
2. Load Balancing
Load Balancers distribute network traffic across multiple backend servers to prevent overloads and ensure high availability. Common algorithms include: - **Round Robin**: Distributes requests sequentially. - **Least Connections**: Routes traffic to the server with the fewest active connections. - **IP Hash**: Hashing client IP addresses to pin requests to the same server (session persistence). - **Geographic Routing**: Directing traffic to servers closest to the user’s physical location.
3. API Gateway
An API Gateway acts as a single entry point for external clients, managing traffic routing, rate limiting, and security headers before requests reach backend microservices. Key features include dynamic routing, JWT authentication, and SSL termination.
4. Content Delivery Network (CDN)
CDNs are globally distributed networks of edge servers that cache static assets (images, JS, CSS, videos) closer to the user to minimize latency and offload traffic from origin servers.
5. Forward vs. Reverse Proxies - **Forward Proxy**: Acts on behalf of the client (hides client IP from the internet, filters content). - **Reverse Proxy**: Acts on behalf of the server (hides backend infrastructure, load balances traffic, handles SSL encryption).
6. Caching and Eviction Policies
Caches store frequently queried data in memory (e.g. Redis, Memcached) to reduce database read overhead. Standard eviction policies include: - **LRU (Least Recently Used)**: Evicts the least recently accessed items first. - **LFU (Least Frequently Used)**: Evicts items with the lowest hit count. - **TTL (Time-to-Live)**: Automatically purges items after a set duration.