distributed-systems

# Distributed Systems Patterns Comprehensive patterns for building reliable distributed systems. Each category has individual rule files in `rules/` loaded on-demand. ## Quick Reference | Category | Rules | Impact | When to Use | |----------|-------|--------|-------------| | [Distributed Locks](#distributed-locks) | 1 | CRITICAL | Fencing tokens, owner validation; Redis/Redlock and Postgres advisory via upstream docs | | [Resilience](#resilience) | 3 | CRITICAL | Circuit breakers, retry with backoff, bulkhead isolation | | [Idempotency](#idempotency) | 1 | HIGH | Idempotency keys; dedup and database-backed storage via upstream docs | | [Rate Limiting](#rate-limiting) | 2 | HIGH | Token bucket, sliding window; SlowAPI integration via upstream docs | | [Edge Computing](#edge-computing) | 2 | HIGH | Edge workers, V8 isolates, CDN caching, geo-routing | | [Event-Driven](#event-driven) | 2 | HIGH | Event sourcing, CQRS, transactional outbox, sagas | **Total: 11 rules across 6 categories.** Removed topics point at first-party sources in [Upstream coverage](#upstream-coverage-do-not-restate); ork-specific scars live in `references/ork-delta.md`. ## Quick Start ```python # Redis distributed lock with Lua scripts async with RedisLock(redis_client, "payment:order-123"): await process_payment(order_id) # Circuit breaker for external APIs @circuit_breaker(failure_threshold=5, recovery_timeout=30) @retry(max_attempts=3, base_delay=1.0) async def call_external_api(): ... # Idempotent API endpoint @router.post("/payments") async def create_payment( data: PaymentCreate, idempotency_key: str = Header(..., alias="Idempotency-Key"), ): return await idempotent_execute(db, idempotency_key, "/payments", process) # Token bucket rate limiting limiter = TokenBucketLimiter(redis_client, capacity=100, refill_rate=10) if await limiter.is_allowed(f"user:{user_id}"): await handle_request() ``` ## Distributed Locks Coordinate exclusive access to resources across multiple service instances. | Rule | File | Key Pattern | |------|------|-------------| | Fencing Tokens | `rules/locks-fencing-tokens.md` | Owner validation, TTL, heartbeat extension | Redis single-node locks, Redlock quorum, and PostgreSQL advisory locks are first-party documented; see [Upstream coverage](#upstream-coverage-do-not-restate). ## Resilience Production-grade fault tolerance for distributed systems. | Rule | File | Key Pattern | |------|------|-------------| | Circuit Breaker | `rules/resilience-circuit-breaker.md` | CLOSED/OPEN/HALF_OPEN states, sliding window | | Retry & Backoff | `rules/resilience-retry-backoff.md` | Exponential backoff, jitter, error classification | | Bulkhead Isolation | `rules/resilience-bulkhead.md` | Semaphore tiers, rejection policies, queue depth | ## Idempotency Ensure operations can be safely retried without unintended side effects. | Rule | File | Key Pattern | |------|------|-------------| | Idempotency Keys | `rules/idempotency-keys.md` | Deterministic hashing, Stripe-style headers | Event-consumer dedup and database-backed idempotency storage follow the Stripe pattern; see [Upstream coverage](#upstream-coverage-do-not-restate). ## Rate Limiting Protect APIs with distributed rate limiting using Redis. | Rule | File | Key Pattern | |------|------|-------------| | Token Bucket | `rules/ratelimit-token-bucket.md` | Redis Lua scripts, burst capacity, refill rate | | Sliding Window | `rules/ratelimit-sliding-window.md` | Sorted sets, precise counting, no boundary spikes | SlowAPI + Redis wiring and tiered limits are first-party documented; see [Upstream coverage](#upstream-coverage-do-not-restate). ## Edge Computing Edge runtime patterns for Cloudflare Workers, Vercel Edge, and Deno Deploy. | Rule | File | Key Pattern | |------|------|-------------| | Edge Workers | `rules/edge-workers.md` | V8 isolate constraints, Web APIs, geo-routing, auth at edge | | Edge Caching | `rules/edge-caching.md` | Cache-aside at edge, CDN headers, KV storage, stale-while-revalidate | ## Event-Driven Event sourcing, CQRS, saga orchestration, and reliable messaging patterns. | Rule | File | Key Pattern | |------|------|-------------| | Event Sourcing | `rules/event-sourcing.md` | Event-sourced aggregates, CQRS read models, optimistic concurrency | | Event Messaging | `rules/event-messaging.md` | Transactional outbox, saga compensation, idempotent consumers | ## Upstream coverage (do not restate) These topics were removed from this skill on 2026-07-31 (wrap-plus-delta thinning) because a first-party source maintains them. Consult the source; do not re-add tutorials here. Ork-specific scars for these topics live in `references/ork-delta.md`. | Topic | First-party source | |-------|--------------------| | Redis single-node locks, Redlock algorithm and quorum | https://redis.io/docs/latest/develop/use/patterns/distributed-locks/ | | PostgreSQL advisory locks (session and transaction level) | https://www.postgresql.org/docs/current/explicit-locking.html#ADVISORY-LOCKS | | Circuit breaker pattern, thresholds, setup and rollout guides | https://learn.microsoft.com/azure/architecture/patterns/circuit-breaker | | Bulkhead pattern deep dive (thread pool, semaphore, tiers) | https://learn.microsoft.com/azure/architecture/patterns/bulkhead | | Retry strategies, exponential backoff, jitter, retry budgets | https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/ and https://tenacity.readthedocs.io | | HTTP and LLM provider error classification (retryable vs not) | https://docs.claude.com/en/api/errors and https://platform.openai.com/docs/guides/error-codes | | Idempotency keys, request dedup, database-backed idempotency | https://docs.stripe.com/api/idempotent_requests | | Token bucket algorithm and Redis rate-limiting patterns | https://redis.io/glossary/rate-limiting/ | | FastAPI distributed rate limiting (SlowAPI middleware, tiers) | https://slowapi.readthedocs.io/ | | LLM fallback chains, provider failover, cost tracking | https://vercel.com/docs/ai-gateway; model ids and pricing at https://docs.claude.com/en/docs/about-claude/pricing | ## Key Decisions | Decision | Recommendation | |----------|----------------| | Lock backend | Redis for speed, PostgreSQL if already using it, Redlock for HA | | Lock TTL | 2-3x expected operation time | | Circuit breaker recovery | Half-open probe with sliding window | | Retry algorithm | Exponential backoff + full jitter | | Bulkhead isolation | Semaphore-based tiers (Critical/Standard/Optional) | | Idempotency storage | Redis (speed) + DB (durability), 24-72h TTL | | Rate limit algorithm | Token bucket for most APIs, sliding window for strict quotas | | Rate limit storage | Redis (distributed, atomic Lua scripts) | ## When NOT to Use No separate event-sourcing/saga/CQRS skills exist; they are rules within distributed-systems. But most projects never need them. | Pattern | Interview | Hackathon | MVP | Growth | Enterprise | Simpler Alternative | |---------|-----------|-----------|-----|--------|------------|---------------------| | Event sourcing | OVERKILL | OVERKILL | OVERKILL | OVERKILL | WHEN JUSTIFIED | Append-only table with status column | | Saga orchestration | OVERKILL | OVERKILL | OVERKILL | SELECTIVE | APPROPRIATE | Sequential service calls with manual rollback | | Circuit breaker | OVERKILL | OVERKILL | BORDERLINE | APPROPRIATE | REQUIRED | Try/except with timeout | | Distributed locks | OVERKILL | OVERKILL | BORDERLINE | APPROPRIATE | REQUIRED | Database row-level lock (SELECT FOR UPDATE) | | CQRS | OVERKILL | OVERKILL | OVERKILL | OVERKILL | WHEN JUSTIFIED | Single model for read/write | | Transactional outbox | OVERKILL | OVERKILL | OVERKILL | SELECTIVE | APPROPRIATE | Direct publish after commit | | Rate limiting | OVERKILL | OVERKILL | SIMPLE ONLY | APPROPRIATE | REQUIRED | Nginx rate limit or cloud WAF | **Rule of thumb:** If you have a single server process, you do not need distributed systems patterns. Use in-process alternatives. Add distribution only when you actually have multiple instances. ## Anti-Patterns (FORBIDDEN) ```python # LOCKS: Never forget TTL (causes deadlocks) await redis.set(f"lock:{name}", "1") # WRONG - no expiry! # LOCKS: Never release without owner check await redis.delete(f"lock:{name}") # WRONG - might release others' lock # RESILIENCE: Never retry non-retryable errors @retry(max_attempts=5, retryable_exceptions={Exception}) # Retries 401! # RESILIENCE: Never put retry outside circuit breaker @retry # Would retry when circuit is open! @circuit_breaker async def call(): ... # IDEMPOTENCY: Never use non-deterministic keys key = str(uuid.uuid4()) # Different every time! # IDEMPOTENCY: Never cache error responses if response.status_code >= 400: await cache_response(key, response) # Errors should retry! # RATE LIMITING: Never use in-memory counters in distributed systems request_counts = {} # Lost on restart, not shared across instances ``` ## Detailed Documentation | Resource | Description | |----------|-------------| | `scripts/` | Templates: lock implementations, circuit breaker, rate limiter | | `references/ork-delta.md` | Ork-specific scars and house decisions kept after the wrap-plus-delta thinning | ## Related Skills - `caching` - Redis caching patterns, cache as fallback - `background-jobs` - Job deduplication, async processing with retry - `observability-monitoring` - Metrics and alerting for circuit breaker state changes - `error-handling-rfc9457` - Structured error responses for resilience failures - `auth-patterns` - API key management, authentication integration