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name: event-driven-architecture description: | Guides event-driven systems—pub/sub, point-to-point, event sourcing, CQRS, schema versioning (Avro/JSON Schema), ordering, partitioning, delivery guarantees, idempotency, exactly-once tradeoffs, transactional outbox/inbox, choreography vs orchestration, sagas, dead-letter queues, replay, stream vs discrete events, microservice boundaries. Use when the user asks for event-driven architecture, event sourcing, CQRS, pub/sub, Kafka events, outbox pattern, idempotent consumer, event choreography, saga orchestration, dead letter queue, or event schema versioning—not microservice code only (microservices-developer), enterprise API/iPaaS only (enterprise-integration-api-developer), EDI (edi-engineer), classified promotion (classified-software-devsecops-engineer), solvers (operations-research-algorithm-developer), generic CRUD (senior-software-engineer).

Event-Driven Architecture

When to Use

• Design event-driven integration between bounded contexts or microservices
• Choose pub/sub vs point-to-point, topics vs queues, and broker capabilities
• Model domain events, integration events, and command vs event semantics
• Apply event sourcing or CQRS at architecture level (not framework tutorials only)
• Define schemas, compatibility rules, and event schema versioning strategy
• Specify ordering, partition keys, and delivery guarantees (at-least-once, etc.)
• Design idempotent consumers, deduplication, and exactly-once tradeoffs
• Implement transactional outbox or inbox for reliable publish/consume
• Decide choreography vs orchestration and saga compensation at pattern level
• Operate dead-letter queues, replay, and stream reprocessing safely
• Distinguish stream processing (Kafka Streams, Flink) from discrete business events

When NOT to Use

• Implement microservice code, gRPC/REST APIs, or twelve-factor deployables only → microservices-developer
• Design enterprise iPaaS hubs, canonical models, B2B partner APIs, or API gateway programs only → enterprise-integration-api-developer
• Map X12/EDIFACT segments, AS2/VAN, or EDI partner certification → edi-engineer
• Build generic application features without event/messaging architecture → senior-software-engineer
• Operate classified air-gapped pipelines, ATO evidence, cleared promotion → classified-software-devsecops-engineer
• Formulate VRP, MIP, scheduling, or optimization solvers → operations-research-algorithm-developer
• CI/CD YAML, GitOps, and release automation only → devops
• Landing zone, VPC, and managed cloud provisioning → cloud-engineer

Related skills

Need	Skill
Service boundaries, gRPC/REST, circuit breakers, contract tests	microservices-developer
Enterprise integration hub, OpenAPI/AsyncAPI, iPaaS, B2B gateways	enterprise-integration-api-developer
EDI standards and partner file exchange	edi-engineer
Application code and refactoring without EDA focus	senior-software-engineer
Classified DevSecOps and artifact promotion	classified-software-devsecops-engineer
OR models, routing, allocation solvers	operations-research-algorithm-developer
Kafka/Rabbit operational platform (brokers, K8s)	platform-engineer, devops
Cross-system ADRs and NFR sign-off	senior-system-architecture
Pipeline security and supply chain	devsecops

Core Workflows

1. Scope and event boundaries

Define event types, producers/consumers, sync vs async boundaries, and non-goals.

See references/event_driven_architecture_scope.md.

2. Messaging and brokers

Select patterns, topics/queues, partitioning, and broker fit (Kafka, Pulsar, SNS/SQS, etc.).

See references/messaging_patterns_and_brokers.md.

3. Event sourcing and CQRS

When to use write models, projections, snapshots, and read-model consistency.

See references/event_sourcing_and_cqrs.md.

4. Reliability, idempotency, outbox

Delivery semantics, deduplication, outbox/inbox, and failure handling.

See references/reliability_idempotency_outbox.md.

5. Orchestration, choreography, sagas

Coordinate long-running flows without turning the bus into a distributed monolith.

See references/orchestration_choreography_sagas.md.

6. Schema governance and operations

Version events, operate DLQs, replay, and observability for event pipelines.

See references/schema_governance_operations.md.

Outputs

• Event catalog — event name, schema version, producer, consumers, SLAs, PII classification
• Context diagram — services, topics/queues, sync fallbacks, trust zones
• Consistency note — outbox/saga/choreography choice with compensation and idempotency keys
• Partitioning and ordering spec — keys, guarantees, hot-partition risks
• Schema compatibility matrix — backward/forward rules, deprecation timeline
• Operations runbook — DLQ drain, replay procedure, lag alerts, poison-message handling

Principles

• Prefer explicit contracts (schemas, AsyncAPI/CloudEvents metadata) over implicit JSON blobs
• Design consumers idempotent by default; treat exactly-once as a bounded, measured goal
• Keep commands and events distinct—events are facts; commands request work
• Avoid chatty orchestration over the bus; sagas compensate, they do not hide missing boundaries
• Make failure observable—correlation ID, structured errors, DLQ with actionable payloads
• Replay is a product feature—document ordering, side effects, and deduplication before reprocessing