System Design

Stateful vs Stateless Architecture

System DesignArchitectureScaling

Understanding session management and architectural trade-offs.

Stateful Architecture

In a stateful architecture, the server retains information (state) about client sessions between requests. The server "remembers" who you are.

✓ Simpler to implement initially
✗ Hard to scale (needs Sticky Sessions)
✗ Single point of failure (memory loss)

Server Memory

Session: User_123

Server must trigger memory lookup

Stateless Architecture

In a stateless architecture, the server does not hold any data between requests. Each request is independent and must contain all necessary information (e.g., via a Token).

✓ Easy horizontal scaling
✓ Resilient (any server can handle any request)
! More complex validation (Cryptography)

Client Request

Token: "I am User_123"

Server validates signature only

Interactive Simulator

Client

Server

💾 Session: 123

Client sends login credentials

Server verifies credentials

Server creates session in memory

Server sends SessionID cookie

Client requests dashboard with Cookie

Server looks up SessionID in memory

Server returns sensitive data

Stateful Sequence Diagram

sequenceDiagram participant C as Client participant S as Server participant M as Memory/DB C->>S: 1. Login S->>M: 2. Create Session (ID: 123) S-->>C: 3. Set-Cookie: sid=123 C->>S: 4. Request (Cookie: sid=123) S->>M: 5. Verify Session 123 M-->>S: 6. Session Valid S-->>C: 7. Response Data

Comparison

Feature	Stateful	Stateless	Winner
Scalability	Hard (Sticky Sessions needed)	Easy (Horizontal scaling)	Stateless
Complexity	Low (Simple logic)	Medium (Token management)	Stateful
Server Memory	High (Stores all sessions)	Low (No storage)	Stateless
Revocation	Instant (Delete session)	Hard (Need blocklist/short try)	Stateful
Bandwidth	Low (Small cookie ID)	Medium (Large tokens)	Stateful
Resilience	Low (Session lost on crash)	High (Any server works)	Stateless

Resources

Title	Type	Link
Stateful vs Stateless Architecture	web	Open
REST API Design: Statelessness	web	Open
System Design: Scaling From Zero to Millions	youtube	Open
Session vs Token Authentication	web	Open

Guide Contributors

ObydulSenior Software Engineer

Edit this page on GitHub↗

Init guide environment...