Stateful VS Stateless

The terms stateful and stateless are often used in software development to describe how systems, applications, or services handle and manage state, which refers to data or information about previous interactions.

Aspect	Stateful	Stateless
State Retention	Yes	No
Request Context	Depends on previous interactions	Independent
Complexity	Higher	Lower
Scaling	Challenging	Easier
Recovery	Requires state restoration	Simple, as no state exists
Examples	Online games, database sessions	RESTful APIs, HTTP, DNS

Stateful

A stateful system or application remembers the state of a client’s interactions across multiple requests or sessions.

Characteristics

• Maintains State: Keeps track of client-specific data or the progress of operations.

• Dependent on Context: Each request is tied to previous interactions.

• Session Management: Often requires mechanisms like session IDs or cookies to maintain state.

• Resource Intensive: Needs additional storage or memory to track state.

Advantages

• Tailored, context-aware experiences for users.

• Efficient for workflows requiring multiple steps.

Disadvantages

• Complex to scale because state must be shared or replicated across servers.

• More challenging to recover from failures as the state needs to be restored.

Examples

• TCP: because bot system need to maintain information about the session it self during it's life cycle.

• Session-based Authentication: because server save all the information about the session using session_id.

Stateless

A stateless system or application does not retain any state between requests. Each request is treated as independent and self-contained.

Characteristics

• No Memory of Previous Interactions: Every request contains all the information needed for processing.

• Easier to Scale: Each request is independent, allowing for horizontal scaling.

• Simpler Recovery: No state to restore after a failure.

• Lightweight: Requires fewer resources since no state is stored.

Advantages

• Scalability and fault tolerance are simpler to achieve.

• Easier to maintain and test due to independence of requests.

Disadvantages

• May require additional data to be sent with each request, increasing overhead.

• Limited suitability for complex workflows requiring state.

Examples

• HTTP Protocol: Each HTTP request is stateless by default.

• RESTful APIs: REST principles advocate for stateless communication.

• Serverless Computing: Functions are invoked and execute without retaining context.

• DNS: Resolves domain names to IP addresses without maintaining state.

Conclusion

• Stateless APIs are the preferred choice for scalable systems because they simplify horizontal scaling and fault tolerance.

• Stateless APIs are inherently easier to scale because each request is self-contained and does not rely on server-side state. This makes it easier to distribute requests across multiple servers.

• Use stateless communication protocols (e.g., REST) and include all necessary data (like authentication tokens or request context) in every API request.

• Use token-based authentication like JWT (JSON Web Tokens), where authentication data is encoded in tokens and verified without server-side state.