Difference Between Stateless and Stateful Applications

Stateless and stateful applications differ mainly in whether they store session data or state information between requests. Here’s a detailed comparison:

1. Stateless Application

• Definition: A stateless application does not store any session information on the server side. Each request is independent and does not rely on any previous requests.
• Characteristics:
  • Independent Requests: Every request must contain all information required for processing, as the server does not remember any user state.
  • High Scalability: Stateless applications are easy to horizontally scale because different requests can be processed by different servers.
  • High Availability: Since there’s no reliance on any particular server for user state, the application remains available even if a node fails.
  • Stateless means not storing session state on the server, not storing data at all.
  • Data can be passed through the client or token, or persisted in the database, but context information between requests will not be kept in the server's memory.
• Typical Use Cases: RESTful APIs, most web applications, microservices architecture.

2. Stateful Application

• Definition: A stateful application stores user session information on the server, meaning subsequent requests rely on data from previous requests.
• Characteristics:
  • Persistent Session: The user’s session state (e.g., login information, shopping cart) is stored on the server, allowing future requests to access this data.
  • Server Dependency: Subsequent requests typically need to be routed to the same server to access the user’s state. This dependency can make scaling and load balancing more complex.
  • Long-Connection Suitability: Stateful applications are suited for scenarios requiring long connections, such as online games or video streaming.
• Typical Use Cases: Online games, video streaming, shopping cart applications, web applications requiring user login.

Summary

• Stateless Applications are ideal for systems requiring high availability and easy scalability, especially in microservice architectures.
• Stateful Applications are suitable for applications that need to track user state or require long sessions, though they generally have lower scalability and fault tolerance.