# Fail Safe

> A design rule that a failing operation leaves the system in the state that causes the least harm.

Record: `architecture:fail-safe`
Kind: principle
Layer: [Correctness Core](https://banes-lab.com/records/layer/correctness-core.md)
Severity: mandatory
Scope: runtime, operation, security
Canonical: https://banes-lab.com/ontology#architecture-fail-safe

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Fail Fast](https://banes-lab.com/records/architecture/fail-fast.md) and before [Fail Secure](https://banes-lab.com/records/architecture/fail-secure.md).

## Repair

- Refactored by: Add Safe Fallback, Stop Unsafe Operation
- Detected by: fallback to unsafe behavior
- Violated by: continuing in unsafe state
- Measured by: unsafe failure modes
- Enforced by: failure-mode tests

## Requires

- [Safe Defaults](https://banes-lab.com/records/lexicon/safe-defaults.md)

## Reinforces

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

## Enables

- [Damage Limitation](https://banes-lab.com/records/lexicon/damage-limitation.md)

## Conflicts with

- [Unsafe Default Continuation](https://banes-lab.com/records/lexicon/unsafe-default-continuation.md)

## In tension with

- [Availability](https://banes-lab.com/records/lexicon/availability.md)

## Tensions

- [Fail Safe / Availability](https://banes-lab.com/records/tension/availability-fail-safe.md)

## Severity

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

## Category

- [Error Handling / Resilience](https://banes-lab.com/records/architecture-category/error-handling-resilience.md)

## Linked from

- [Execution joins the halves](https://banes-lab.com/software-architecture/principles/execution-joins-the-halves.md)
- [Error Handling / Resilience](https://banes-lab.com/ontology/principles/architecture-category-error-handling-resilience.md)
- [Core Vocabulary](https://banes-lab.com/ontology/lexicon/lexicon-category-core-vocabulary.md)
- [Error Handling / Resilience](https://banes-lab.com/ontology/lexicon/lexicon-category-error-handling-resilience.md)
- [Quality Attributes](https://banes-lab.com/ontology/lexicon/lexicon-category-quality-attributes.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)