# Replication

> A mechanism that keeps copies of data on several nodes under a declared consistency policy, such as a write quorum.

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

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Redundancy](https://banes-lab.com/records/architecture/redundancy.md) and before [Auto-Scaling](https://banes-lab.com/records/architecture/auto-scaling.md).

## Repair

- Refactored by: Add Replica, Define Consistency Model
- Detected by: SPOF data stores
- Violated by: unreplicated critical state
- Measured by: replication lag, replica count
- Enforced by: infrastructure policy

## Requires

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

## Reinforces

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

## Enables

- [Read Scaling](https://banes-lab.com/records/lexicon/read-scaling.md)
- [Failover](https://banes-lab.com/records/architecture/failover.md)

## Conflicts with

- [Single Copy State](https://banes-lab.com/records/lexicon/single-copy-state.md)

## In tension with

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

## Tensions

- [Replication / Consistency Lag](https://banes-lab.com/records/tension/consistency-lag-replication.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)

## Required by

- [Read Replica](https://banes-lab.com/records/architecture/read-replica.md)

## Linked from

- [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)
- [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)