---
title: Shared System Invariants
document_id: shared-system-invariants
owner: Product Spec Maintainers
status: draft
created: 2026-03-16
last_updated: 2026-03-16
---

# Shared System Invariants

Feature PRDs should reference the relevant invariant IDs from this document explicitly and explain any feature-local constraints or exceptions. If a feature cannot preserve one of these invariants, the exception should be called out directly in the PRD and design review.

## How to Use

- Cite applicable invariant IDs in the PRD `System Invariants` section.
- Reuse these invariants in architecture reviews and scenario validation.
- Add feature-local invariants only when they tighten or extend these global expectations.

## INV-GLOBAL-001 Acknowledged Writes Are Durable

Statement:
No write acknowledged as committed by the system may be lost during normal operation, restart, failover, or recovery within the documented durability model.

Rationale:
Durability is the baseline trust contract for database and infrastructure products.

## INV-GLOBAL-002 Commit Visibility Follows Defined Ordering

Statement:
When a feature depends on transactional or ordered state changes, externally visible effects must follow the documented commit or sequencing rules of the source system.

Rationale:
Ordering drift creates correctness bugs that are difficult for application teams to detect or repair.

## INV-GLOBAL-003 Metadata Must Remain Readable and Durable

Statement:
Configuration, schema metadata, checkpoints, and other control metadata required for safe operation must remain durable and recoverable across restart and upgrade boundaries.

Rationale:
Operational recovery depends on trustworthy metadata, not only on user data durability.

## INV-GLOBAL-004 Silent Corruption Is Unacceptable

Statement:
The system must not silently corrupt, truncate, misroute, or reinterpret user data or control metadata without detection or operator-visible signals.

Rationale:
Silent correctness failures are more damaging than explicit, observable faults.

## INV-GLOBAL-005 Unhealthy States Must Be Observable

Statement:
Materially unhealthy states such as stalled progress, replication failure, backlog growth, degraded quorum, or persistent retry loops must be detectable through supported observability surfaces.

Rationale:
Operators cannot manage distributed systems safely if failure is hidden or ambiguous.

## INV-GLOBAL-006 Recovery Paths Must Be Operationally Safe

Statement:
Restart, failover, repair, and replacement workflows must converge to a valid operating state without requiring undocumented manual intervention in normal recovery scenarios.

Rationale:
Recoverability is part of product correctness, not only an operational convenience.

## INV-GLOBAL-007 Upgrades Must Preserve Control

Statement:
Supported upgrade workflows must preserve service control, management access, and the integrity of persisted state throughout the documented upgrade path.

Rationale:
An upgrade path that compromises manageability or state safety is not operationally viable.

## INV-GLOBAL-008 Mixed-Version Operation Must Be Bounded and Defined

Statement:
When rolling upgrades or staggered deployments are supported, mixed-version behavior must remain within explicitly documented compatibility boundaries.

Rationale:
Distributed systems often run temporarily mixed-version, and undefined behavior in that state creates rollout risk.

## INV-GLOBAL-009 Authorization Boundaries Must Hold Under Failure

Statement:
Failures, retries, partial outages, and degraded modes must not bypass defined authentication, authorization, or tenancy boundaries.

Rationale:
Security guarantees must survive the same failure conditions as availability guarantees.

## INV-GLOBAL-010 Operator Actions Must Be Traceable

Statement:
Privileged control-plane actions that materially change system state should remain attributable through durable logs, audit surfaces, or equivalent operator-visible records.

Rationale:
Traceability is required for incident response, compliance review, and safe team operations.