# Failover

> A mechanism that switches traffic or reads to a standby instance when the active one fails.

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

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Health Checks](https://banes-lab.com/records/architecture/health-checks.md) and before [Redundancy](https://banes-lab.com/records/architecture/redundancy.md).

## Repair

- Refactored by: Add Replica, Add Failover Routing
- Detected by: single active dependency with no failover
- Violated by: no alternate instance/path for critical dependency
- Measured by: failover time, [availability](https://banes-lab.com/records/lexicon/availability.md)
- Enforced by: disaster recovery tests

## Requires

- [Redundancy](https://banes-lab.com/records/architecture/redundancy.md)
- [Health Detection](https://banes-lab.com/records/lexicon/health-detection.md)

## Reinforces

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

## Enables

- [Continuity During Failure](https://banes-lab.com/records/lexicon/continuity-during-failure.md)

## Conflicts with

- [Single Instance Dependency](https://banes-lab.com/records/lexicon/single-instance-dependency.md)

## In tension with

- [Consistency](https://banes-lab.com/records/architecture/consistency.md)

## Tensions

- [Failover / Consistency](https://banes-lab.com/records/tension/consistency-failover.md)

## Severity

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

## Category

- [Self-Healing / Recovery / Deployment Safety](https://banes-lab.com/records/architecture-category/self-healing-recovery-deployment-safety.md)

## Enabled by

- [Service Discovery](https://banes-lab.com/records/architecture/service-discovery.md)
- [Replication](https://banes-lab.com/records/architecture/replication.md)

## Linked from

- [Runtime Discovery / Dynamic Binding](https://banes-lab.com/ontology/principles/architecture-category-runtime-discovery-dynamic-binding.md)
- [Error Handling / Resilience](https://banes-lab.com/ontology/principles/architecture-category-error-handling-resilience.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)
- [Quality Attributes](https://banes-lab.com/ontology/lexicon/lexicon-category-quality-attributes.md)
- [Self-Healing / Recovery / Deployment Safety](https://banes-lab.com/ontology/lexicon/lexicon-category-self-healing-recovery-deployment-safety.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)