# Fault Tolerance

> The degree to which a system keeps operating correctly when some of its components fail.

Record: `architecture:fault-tolerance`
Kind: quality-attribute
Layer: [Correctness Core](https://banes-lab.com/records/layer/correctness-core.md)
Severity: contextual
Scope: service, system, infrastructure
Canonical: https://banes-lab.com/ontology#architecture-fault-tolerance

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Graceful Degradation](https://banes-lab.com/records/architecture/graceful-degradation.md) and before [Resilience](https://banes-lab.com/records/architecture/resilience.md).

## Repair

- Refactored by: Add Retry, [Failover](https://banes-lab.com/records/architecture/failover.md), [Redundancy](https://banes-lab.com/records/architecture/redundancy.md)
- Detected by: no retry/failover/fallback for critical path
- Violated by: unrecoverable dependency failure
- Measured by: failure recovery rate, [availability](https://banes-lab.com/records/lexicon/availability.md)
- Enforced by: resilience tests

## Requires

- [Redundancy](https://banes-lab.com/records/architecture/redundancy.md)
- [Error Handling](https://banes-lab.com/records/architecture/error-handling.md)

## Reinforces

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

## Enables

- [Continued Operation Under Failure](https://banes-lab.com/records/lexicon/continued-operation-under-failure.md)

## Conflicts with

- [Single Point of Failure](https://banes-lab.com/records/lexicon/single-point-of-failure.md)

## In tension with

- [Cost](https://banes-lab.com/records/lexicon/cost.md)

## Tensions

- [Fault Tolerance / Cost](https://banes-lab.com/records/tension/cost-fault-tolerance.md)

## Severity

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

## Category

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

## Reinforced by

- [Leader Election](https://banes-lab.com/records/architecture/leader-election.md)
- [Consensus](https://banes-lab.com/records/architecture/consensus.md)
- [Graceful Degradation](https://banes-lab.com/records/architecture/graceful-degradation.md)
- [Retry Pattern](https://banes-lab.com/records/architecture/retry-pattern.md)
- [Circuit Breaker Pattern](https://banes-lab.com/records/architecture/circuit-breaker-pattern.md)
- [Chaos Engineering](https://banes-lab.com/records/architecture/chaos-engineering.md)
- [RAID Redundancy](https://banes-lab.com/records/architecture/raid-redundancy.md)

## Linked from

- [Control / Coordination / Centralization](https://banes-lab.com/ontology/principles/architecture-category-control-coordination-centralization.md)
- [Error Handling / Resilience](https://banes-lab.com/ontology/principles/architecture-category-error-handling-resilience.md)
- [Observability / Auditability / Traceability](https://banes-lab.com/ontology/principles/architecture-category-observability-auditability-traceability.md)
- [Self-Healing / Recovery / Deployment Safety](https://banes-lab.com/ontology/principles/architecture-category-self-healing-recovery-deployment-safety.md)
- [Transactions / State / Concurrency](https://banes-lab.com/ontology/principles/architecture-category-transactions-state-concurrency.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)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)