Stateful vs. Stateless Applications in Containers
Definitions
Stateless applications do not retain any data or session information between requests. Each request is handled independently.
Stateful applications maintain session state or persistent data between operations, either in-memory or stored externally.
Stateless apps are ideal for scaling. Stateful apps require careful management of persistent storage.
Stateless Applications
- Each instance is identical and independent
- Easily scalable and resilient
- No reliance on local storage or session data
- Common in APIs, web servers, microservices
- Can be quickly recreated or relocated
Stateful Applications
- Store data, sessions, or user context between requests
- Require persistent storage (volumes, databases)
- Examples: databases, caches, message queues
- Less flexible for dynamic scaling
- Often need sticky sessions or storage replication
Comparison Table
| Aspect | Stateless | Stateful |
|---|---|---|
| Session/Data Storage | None or external | Maintains internal or persistent state |
| Scaling | Horizontal scaling is easy | Requires special handling (storage, sessions) |
| Failure Recovery | Recoverable by spinning up new instances | Needs data recovery or state syncing |
| Deployment | Fast and uniform | Slower, more complex |
| Examples | Frontend apps, APIs | Databases, StatefulSets |
In Kubernetes
- Stateless: Use Deployments for easy scaling and rollouts
- Stateful: Use StatefulSets with Persistent Volumes for stable identities and storage