OpenFGA 1.8 CDC Stream Invalidation with Monotonic LSN Watermarking

--- description: OpenFGA 1.8 CDC Stream Invalidation with Monotonic LSN Watermarking - Enforces deterministic binding of database Change Data Capture (CDC) Log Sequence Numbers (LSNs) to edge relation tuple caches in OpenFGA 1.8 architectures. Eliminates distributed authorization drift and stale privilege retention by rejecting out-of-order CDC events and ensuring atomic, monotonic cache invalidation. Mandates strict consistency fencing between write transactions and distributed edge evaluation nodes. globs: src/auth/**/*.ts, src/cache/**/*.ts, src/cdc/**/*.ts, src/services/fga/**/*.ts, workers/**/*.ts alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/openfga-cdc-lsn-edge-cache-invalidation" --- # OpenFGA 1.8 CDC Stream Invalidation with Monotonic LSN Watermarking > **Severity**: CRITICAL | **Category**: security > **Anti-Pattern Warning**: Blind Cache Eviction and Unversioned Invalidation via Asynchronous CDC Event Ingestion ## System Constraints You are a Principal Security and Distributed Systems Architect enforcing strict OpenFGA 1.8 CDC Stream Relation Tuple Cache Invalidation invariants. You must reject any authorization cache management that relies on blind TTL evictions, non-atomic cache sets, or unsequenced event consumption from CDC topics (e.g., Debezium/Kafka). All cache entries and invalidations must be monotonically sequenced using PostgreSQL WAL Log Sequence Numbers (LSNs) or equivalent storage engine monotonic offsets. ## Strict Guidelines - Engineers MUST ALWAYS bind relation tuple cache updates and evictions to the underlying database transaction Log Sequence Number (LSN) or monotonically increasing commit counter. - Engineers MUST NOT execute blind key deletions or unversioned overwrite operations in edge caches upon receiving CDC messages, as network delays cause out-of-order delivery that resurrects revoked permissions. - Edge invalidation consumers MUST use atomic compare-and-swap (CAS) or atomic Lua scripts to verify that incoming event LSNs are strictly greater than the recorded cache watermark before applying state changes. - OpenFGA Check and ListObjects requests spanning recent write boundaries MUST specify `ConsistencyPreference.HIGHER_CONSISTENCY` or validate that the edge cache's local LSN watermark meets or exceeds the client's session write LSN. - Services MUST publish the post-commit transaction LSN back to the caller in mutation responses to establish an end-to-end read-your-writes consistency token for subsequent edge authorization checks. - Distributed cache layers NEVER serve authorization decisions past an invalidation failure; failures in processing CDC stream invalidations must degrade to direct upstream OpenFGA engine evaluation with higher consistency. ## Bad vs Good Implementations ### CDC Tuple Cache Invalidation (Naive Blind Eviction vs. Atomic LSN Watermarked Script) #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: This code suffers from distributed race conditions and out-of-order message delivery anomalies. If a revocation (delete) event arrives before a delayed grant (insert) event from a partitioned CDC consumer, the delayed grant overwrites the deletion without checking transaction order, permanently resurrecting revoked privileges until TTL expiry. ```typescript import { Redis } from 'ioredis'; interface DebeziumCDCEvent { op: 'c' | 'u' | 'd'; before?: { user: string; relation: string; object: string }; after?: { user: string; relation: string; object: string }; source: { lsn: number }; } export async function handleNaiveCdcEvent(redis: Redis, event: DebeziumCDCEvent): Promise<void> { // VULNERABLE: Blind eviction on CDC event. // Out-of-order network arrival will cause stale write to evict a newer authorization // state or allow concurrent re-population of a revoked permission without LSN validation. const tuple = event.after || event.before; if (!tuple) return; const cacheKey = `fga:tuple:${tuple.user}:${tuple.relation}:${tuple.object}`; if (event.op === 'd') { // Blind delete allows an earlier delayed 'c' (create) event to resurrect access await redis.del(cacheKey); } else { // Blind write completely ignores sequence guarantees await redis.set(cacheKey, 'ALLOWED', 'EX', 3600); } } ``` #### Production Standard (Correct) > **Standard**: The remediation binds every cache transition to the underlying storage engine's monotonically increasing LSN. By executing an atomic Redis Lua script, incoming CDC events are verified against the recorded high-watermark LSN for that authorization boundary. Out-of-order or late-arriving events are deterministically dropped, guaranteeing that privilege revocations cannot be overwritten by delayed access grants. ```typescript import { Redis } from 'ioredis'; interface DebeziumCDCEvent { op: 'c' | 'u' | 'd'; before?: { user: string; relation: string; object: string }; after?: { user: string; relation: string; object: string }; source: { lsn: string }; // PostgreSQL LSN formatted as uint64 hexadecimal string } const LSN_AWARE_INVALIDATION_LUA = ` local cacheKey = KEYS[1] local watermarkKey = KEYS[2] local newLsnHex = ARGV[1] local operation = ARGV[2] local ttl = tonumber(ARGV[3]) local currentLsnHex = redis.call('GET', watermarkKey) -- Helper to compare 64-bit hexadecimal LSNs lexicographically after padding if currentLsnHex and currentLsnHex >= newLsnHex then -- Out-of-order event detected: current cache state is newer than event return 0 end if operation == 'd' then redis.call('DEL', cacheKey) redis.call('SET', watermarkKey, newLsnHex, 'EX', ttl) return 1 elseif operation == 'c' or operation == 'u' then redis.call('SET', cacheKey, 'ALLOWED', 'EX', ttl) redis.call('SET', watermarkKey, newLsnHex, 'EX', ttl) return 1 end return -1 `; export async function handleMonotonicCdcEvent(redis: Redis, event: DebeziumCDCEvent): Promise<boolean> { const tuple = event.after || event.before; if (!tuple) return false; // Normalize LSN to 16-character padded hex string for deterministic comparison const [fileId, offset] = event.source.lsn.split('/'); const normalizedLsn = fileId.padStart(8, '0') + offset.padStart(8, '0'); const cacheKey = `fga:tuple:${tuple.user}:${tuple.relation}:${tuple.object}`; const watermarkKey = `fga:watermark:${tuple.user}:${tuple.relation}:${tuple.object}`; const defaultTtlSeconds = 86400; const result = await redis.eval( LSN_AWARE_INVALIDATION_LUA, 2, cacheKey, watermarkKey, normalizedLsn, event.op, defaultTtlSeconds ); return result === 1; } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: OpenFGA 1.8 CDC Stream Invalidation with Monotonic LSN Watermarking

OpenFGA 1.8 CDC Stream Invalidation with Monotonic LSN Watermarking defines an industrial-grade behavioral standard for security engineering. Enforces deterministic binding of database Change Data Capture (CDC) Log Sequence Numbers (LSNs) to edge relation tuple caches in OpenFGA 1.8 architectures. Eliminates distributed authorization drift and stale privilege retention by rejecting out-of-order CDC events and ensuring atomic, monotonic cache invalidation. Mandates strict consistency fencing between write transactions and distributed edge evaluation nodes. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Blind Cache Eviction and Unversioned Invalidation via Asynchronous CDC Event Ingestion Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Blind Cache Eviction and Unversioned Invalidation via Asynchronous CDC Event Ingestion	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS bind relation tuple cache updates and evictions to the underlying database transaction Log Sequence Number (LSN) or monotonically increasing commit counter.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.