Stateful vs Stateless Architecture
A stateless service does not rely on a particular server remembering previous requests; each request carries or retrieves what it needs. Stateful services keep session or workflow information in local memory or another tied-to-instance store. Stateless application servers are easier to add, replace, and route around. Stateful designs can be useful, but need sticky routing or shared durable state when instances change.
Key idea
Stateless servers are interchangeable because state lives outside the request process.
See it in one picture
Follow the arrowsAny server can help
Memory stays nearby
Real-world example
A stateless API can verify a token and read a shared session store no matter which instance receives the request. A stateful chat connection may stay on one server while a shared broker coordinates events.
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