# Statelessness

> A design rule that a handler keeps no request state between calls, so any instance can serve any request.

Record: `architecture:statelessness`
Kind: principle
Layer: [Performance Core](https://banes-lab.com/records/layer/performance-core.md)
Severity: recommended
Scope: service, process, handler
Canonical: https://banes-lab.com/ontology#architecture-statelessness

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Caching](https://banes-lab.com/records/architecture/caching.md) and before [Concurrency](https://banes-lab.com/records/architecture/concurrency.md).

## Repair

- Refactored by: Move State to Store, Use Token/Session Store
- Detected by: mutable static/session-local state
- Violated by: correctness depends on in-memory instance state
- Measured by: state externalization coverage
- Enforced by: architecture tests

## Requires

- [Externalized State](https://banes-lab.com/records/lexicon/externalized-state.md)

## Reinforces

- [Horizontal Scaling](https://banes-lab.com/records/architecture/horizontal-scaling.md)
- [Resilience](https://banes-lab.com/records/architecture/resilience.md)

## Enables

- [Load Balancing](https://banes-lab.com/records/architecture/load-balancing.md)
- [Auto-Scaling](https://banes-lab.com/records/architecture/auto-scaling.md)

## Conflicts with

- [Instance Affinity](https://banes-lab.com/records/lexicon/instance-affinity.md)
- [Temporal Coupling](https://banes-lab.com/records/architecture/temporal-coupling.md)

## In tension with

- [State Access Latency](https://banes-lab.com/records/lexicon/state-access-latency.md)

## Tensions

- [Statelessness / State Access Latency](https://banes-lab.com/records/tension/state-access-latency-statelessness.md)

## Severity

- [recommended](https://banes-lab.com/records/vocabulary/severity-recommended.md)

## Category

- [Scalability / Performance / Optimization](https://banes-lab.com/records/architecture-category/scalability-performance-optimization.md)

## Linked from

- [Computation and resource](https://banes-lab.com/software-architecture/principles/computation-and-resource.md)
- [Separate, trade, or mitigate](https://banes-lab.com/software-architecture/principles/separate-trade-or-mitigate.md)
- [The principle architecture](https://banes-lab.com/software-architecture/glossary/the-principle-architecture.md)
- [Anti-patterns](https://banes-lab.com/ontology/principles/architecture-category-anti-patterns.md)
- [Error Handling / Resilience](https://banes-lab.com/ontology/principles/architecture-category-error-handling-resilience.md)
- [Scalability / Performance / Optimization](https://banes-lab.com/ontology/principles/architecture-category-scalability-performance-optimization.md)
- [Self-Healing / Recovery / Deployment Safety](https://banes-lab.com/ontology/principles/architecture-category-self-healing-recovery-deployment-safety.md)
- [Scalability / Performance / Optimization](https://banes-lab.com/ontology/lexicon/lexicon-category-scalability-performance-optimization.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)