Cross-cutting Concepts

Circuit Breaker

The shared Opossum implementation offers the decorator @CircuitBreaker(name, fallbackMethod) for the service clients and the factory createCircuitBreaker(...) for the ClusterGateway, which knows ConfigClient and FluidsClient only via IConfigLookup and IAnalyze respectively; the fallback publishes failed, but no synthetic results.

Status Telemetry via Kafka

KafkaClient implements IEventPublisher and encapsulates the three topics: the algorithm services produce status and results, the coordinator consumes both for its read model, EMS the upstream status.

Server-Sent Events

AnalysisService holds a process-local ReplaySubject(50) per runId and forwards status, result and overall as SSE; after the overall the UI closes the stream.

Invalidation of Outdated EMS Runs

Every EMS run has a monotonically increasing version: failure or retry of an upstream increments it and invalidates the running attempt, which then discards its result.

Failure Simulation

POST /simulation/:cluster/down|up sets the state of a service whose /analyze then responds with 503 – a PoC variant of the Test Harness pattern according to Nygard (chapter 5). In production the trigger is a real failure; the breakers behave the same.

Interfaces as Contracts (Provided/Required)

The contracts are separated from the components and live in @shared/contracts; the rest of the library (http, kafka, circuit-breaker, simulation, …) is infrastructure. Required interfaces are injected as an abstraction: services and ClusterGateway depend via @Inject(TOKEN) on the contract, not on a client class. The @Module is the assembler that binds each token to an implementation – tokens instead of abstract classes, because TypeScript interfaces do not exist at runtime and Fluids needs two bindings of the same IAnalyze. Provided interfaces are enforced by implements on the controller; every service publishes them as OpenAPI 3 under /api-docs-json (UI under /api-docs), the exported documents are in docs/api/. The Kafka topics are typed via TopicContracts, so that a message can only be published on its topic. Limitation: the TypeScript contract is bound to language and monorepo (TS-1); only the generated OpenAPI document is independent of the component.