distributed-systems-patterns ยท diff
git:20260519.bd4658a to git:20260712.a867952
30 added, 23 removed. Audit A to A.
---
name: distributed-systems-patterns
- description: Use when designing or reviewing multi-service, message-driven, or eventually
- consistent systems. Covers service boundaries, consistency tradeoffs, event workflows,
- outbox and inbox patterns, sagas, ordering, and idempotency.
+ description: Use when designing or reviewing multi-service, message-driven, or eventually consistent systems. Covers service boundaries, consistency tradeoffs, event workflows, outbox and inbox patterns, sagas, ordering, and idempotency.
metadata:
portable: true
compatible_with:
- - Codex
+ - claude-code
- codex
---
# Distributed Systems Patterns
Acknowledgement: Shared by Peter Bamuhigire, techguypeter.com, +256 784 464178.
<!-- dual-compat-start -->
## Use When
- Use when designing or reviewing multi-service, message-driven, or eventually consistent systems. Covers service boundaries, consistency tradeoffs, event workflows, outbox and inbox patterns, sagas, ordering, and idempotency.
- - The task needs reusable judgment, domain constraints, or a proven workflow rather than ad hoc advice.
## Do Not Use When
- - The task is unrelated to `distributed-systems-patterns` or would be better handled by a more specific companion skill.
- - The request only needs a trivial answer and none of this skill's constraints or references materially help.
+ - The change is a single-process transaction with no remote dependency, asynchronous delivery, or independently failing component.
+ - The task is mainly service decomposition or API shape; use `system-architecture-design` or `api-design-first` and return here for cross-boundary failure semantics.
## Required Inputs
- - Gather relevant project context, constraints, and the concrete problem to solve; load `references` only as needed.
- - Confirm the desired deliverable: design, code, review, migration plan, audit, or documentation.
+ | Input | Required | Why it matters |
+ |---|---|---|
+ | Workflow steps and system boundaries | yes | Identifies where atomicity ends and partial failure begins |
+ | Delivery, ordering, and consistency requirements | yes | Determines idempotency, sequencing, and reconciliation choices |
+ | Failure and recovery expectations | yes | Sets timeout, retry, compensation, and operator intervention rules |
+ | Throughput and latency constraints | conditional | Tests whether the coordination pattern is viable |
## Workflow
- - Read this `SKILL.md` first, then load only the referenced deep-dive files that are necessary for the task.
- - Apply the ordered guidance, checklists, and decision rules in this skill instead of cherry-picking isolated snippets.
- - Produce the deliverable with assumptions, risks, and follow-up work made explicit when they matter.
+ Draw state transitions and ownership boundaries, enumerate failure windows, choose consistency and coordination patterns, define idempotency and recovery, then verify duplicate, reordered, delayed, and partially applied events.
## Quality Standards
- - Keep outputs execution-oriented, concise, and aligned with the repository's baseline engineering standards.
- - Preserve compatibility with existing project conventions unless the skill explicitly requires a stronger standard.
- - Prefer deterministic, reviewable steps over vague advice or tool-specific magic.
-
- ## Anti-Patterns
-
- - Treating examples as copy-paste truth without checking fit, constraints, or failure modes.
- - Loading every reference file by default instead of using progressive disclosure.
+ Every remote interaction has a timeout and failure policy. Every retried side effect has an idempotency rule. Consistency claims state their scope, and recovery does not assume exactly-once delivery.
## Outputs
- - A concrete result that fits the task: implementation guidance, review findings, architecture decisions, templates, or generated artifacts.
- - Clear assumptions, tradeoffs, or unresolved gaps when the task cannot be completed from available context alone.
- - References used, companion skills, or follow-up actions when they materially improve execution.
+ | Output | Consumer | Acceptance condition |
+ |---|---|---|
+ | Distributed workflow model | Architecture and implementation teams | Shows state ownership, message boundaries, consistency guarantees, and failure windows |
+ | Failure-handling contract | Service owners | Defines timeout, retry, deduplication, compensation, replay, and reconciliation behavior |
+ | Verification scenarios | Test and operations teams | Cover duplicates, reordering, concurrency, dependency outage, and partial completion |
## Evidence Produced
| Category | Artifact | Format | Example |
|----------|----------|--------|---------|
| Operability | Service consistency and idempotency note | Markdown doc covering chosen consistency model, idempotency keys, and saga sequences | `docs/dist/consistency-note-checkout.md` |
| Operability | Failure-mode catalogue | Markdown doc listing partition, retry, and replay failure modes with mitigations | `docs/dist/failure-modes-checkout.md` |
## References
- Use the `references/` directory for deep detail after reading the core workflow below.
- Load `references/event-driven-architecture.md` for event choreography, event contracts, brokers, and asynchronous workflow design.
- Load `references/realtime-systems.md` for WebSocket, SSE, pub/sub, and realtime delivery concerns.
<!-- dual-compat-end -->
Use this skill when a design crosses process, service, queue, or region boundaries. The goal is to keep distributed complexity deliberate and bounded rather than accidental.
## Load Order
1. Load `world-class-engineering`.
2. Load `system-architecture-design` first for the overall shape.
3. Load this skill only when the system genuinely needs multiple services, asynchronous workflows, or weakly consistent boundaries.
## Decision Workflow
### 1. Justify Distribution
State why distribution is necessary:
- team ownership and release independence
- scaling asymmetry
- fault isolation
- compliance or tenancy isolation
- long-running or bursty workflows
If none of these are strong, prefer a modular monolith.
### 2. Define Boundaries and Contracts
For each service or asynchronous component, define:
- owned data
- API or event contracts
- consistency expectation
- failure effect on upstream and downstream flows
- observability and ownership requirements
### 3. Choose Interaction Patterns
Use:
- synchronous calls when the caller needs immediate confirmation
- messaging when work is slow, bursty, or naturally eventual
- outbox and inbox patterns when reliability across boundaries matters
- sagas or compensations when one business workflow spans multiple durable states
### 4. Design Consistency and Recovery
Make explicit:
- source of truth
- ordering requirements
- deduplication strategy
- reconciliation path
- timeout and retry policy
- compensation or manual repair path
### 5. Prove the Design
Before calling it production-ready, provide:
- consistency model
- failure-mode examples
- idempotency and replay notes
- contract evolution rules
- operational signals for stuck or divergent workflows
## Non-Negotiable Standards
### Service Boundaries
- Each service owns its data and rules.
- Do not share databases across services as a convenience.
- Keep contracts narrow and versionable.
- Avoid chatty request chains on critical paths.
### Messaging
- Assume at-least-once delivery unless proven otherwise.
- Design consumers to be idempotent and replay-safe.
- Define ordering needs explicitly; unordered by default is safer to assume.
- Include correlation IDs and causation metadata.
### Consistency
- Strong consistency has operational cost; use it where business correctness needs it.
- Eventual consistency requires visible user and operator handling.
- If divergence is possible, define reconciliation before shipping.
### Sagas and Compensation
- Use compensation when the workflow spans multiple irreversible boundaries.
- Compensation must be explicit, auditable, and tested.
- Never describe a workflow as atomic if it crosses systems that cannot commit atomically.
## Deliverables
For distributed-system work, produce:
- service and ownership map
- contract list
- consistency decision table
- event and retry flow notes
- reconciliation or compensation plan
- stuck-workflow and replay detection signals
## Review Checklist
- [ ] Distribution is justified by real constraints.
- [ ] Data ownership is explicit and not undermined by shared persistence shortcuts.
- [ ] Idempotency and replay behavior are defined.
- [ ] Ordering assumptions are explicit.
- [ ] Consistency and compensation strategy match business risk.
- [ ] Operational detection exists for stuck, duplicated, or divergent workflows.
## References
- [references/consistency-decision-matrix.md](references/consistency-decision-matrix.md): How to choose synchronous, asynchronous, strong, or eventual consistency.
- [references/messaging-checklist.md](references/messaging-checklist.md): Event, queue, and saga review prompts.
+
+ ## Capability contract
+ Model boundaries, messages, and failure semantics by default. Do not provision brokers, replay events, or mutate production state unless explicitly authorised.
+
+ ## Degraded mode
+ If topology or failure evidence is unavailable, return a read-only pattern comparison and assumptions register; withhold recommendations dependent on unknown delivery guarantees.
+
+ ## Domain Anti-Patterns
+ - Assuming exactly-once delivery. Fix: define idempotency and deduplication.
+ - Sharing one database across autonomous services. Fix: assign data ownership.
+ - Publishing before the state change commits. Fix: use a transactional outbox.
+ - Retrying non-idempotent commands blindly. Fix: add keys and retry limits.
+ - Omitting poison-message handling. Fix: define dead-letter and replay controls.