What does stateless mean in REST?
Stateless means the server does not remember anything about previous requests. Every request from the client must include all the information the server needs to handle it, such as who the user is. Because nothing is stored between calls, any server can handle any request, which makes REST APIs easy to scale.
- Stateless means the server keeps no client session between requests.
- Each request carries all the information needed to process it, such as a token.
- Statelessness makes APIs easier to scale across many servers.
Why it matters
If the server kept session state in memory, a follow up request would have to hit the exact same server that stored it. With statelessness, requests can go to any server behind a load balancer, so you can add more servers freely.
- Each request carries its own auth, usually a token in a header.
- Any server can serve any request, which helps horizontal scaling.
- Failures are simpler because there is no lost session to recover.
A great point to add is that statelessness is what makes REST scale well behind load balancers. Tying the concept to scaling shows you understand why the rule exists, not just the definition.
Frequently asked questions
How do stateless APIs handle authentication?
The client sends a credential like a token with every request, so the server can authenticate it without storing session state between calls.
Why does statelessness help scaling?
Since no request depends on server stored session data, any server can handle any request, making it easy to add servers behind a load balancer.
Common follow up questions
Related interview questions
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