Adapted from Mastering System Design from Basics to Cracking Interviews (Udemy) — https://www.udemy.com/course/mastering-system-design-from-basics-to-cracking-interviews/
How Clients and Servers Communicate
Communication follows a basic sequence:
- Client sends a request (HTTP, SQL, etc.).
- Request is transmitted over the network.
- Server receives and processes the request.
- Server sends a response.
- Client receives and processes the response.
The Request-Response Cycle (HTTP Example)
Browser requests https://example.com
- DNS resolves domain to IP
address
- Browser sends HTTP GET request to web server
- Web server processes request (queries DB if needed)
- Server sends HTTP response (e.g., 200 OK)
- Browser renders the webpage
Synchronous vs Asynchronous Communication
| Pattern | Description | Example |
|---|---|---|
| Synchronous | Client waits for a response before proceeding (Blocking). | REST APIs, Traditional web apps. |
| Asynchronous | Client doesn't wait and can perform other tasks (Non-Blocking). | WebSockets, Background jobs, AJAX. |
Synchronous Communication (Blocking)
Asynchronous Communication (Non-Blocking)
Stateless vs Stateful Servers
Stateless Servers
- No memory of past interactions; each request is independent.
- Benefits: Easily scalable, simple caching, better load balancing.
- Example: REST APIs, HTTP servers.
Stateful Servers
- Maintain session information across multiple requests.
- Benefits: Personalized user experiences, seamless state tracking.
- Example: Multiplayer games, Real-time banking.
Importance of DNS in Large-Scale Systems
DNS isn't just for naming; it's a tool for traffic management:
- Ensuring High Availability: Load balancing using DNS.
- DNS Failover: Automatically switching to a passive server if the primary goes down.
- CDN Integration: Directing users to the nearest "edge" node for content delivery.