Event-Driven-Architecture

Overview Broker and mediator topology are the two core styles for structuring event-driven architectures, differing in who controls the flow of events between components. In a broker topology, events flow directly between producers and consumers through a distributed broker with no central authority, while a mediator topology routes every event through a central orchestrator that dictates the sequence of steps. The choice determines how easily the system scales versus how easily complex, stateful workflows can be managed and debugged. ...

Overview Orchestration and choreography are two ways to coordinate multiple services in a distributed system or workflow. Orchestration relies on a central controller that explicitly directs each step, while choreography lets services independently respond to event reactions with no single component in charge. The choice shapes coupling, visibility, and how easily the workflow evolves over time. Comparison Diagram OrchestrationChoreographyOrchestratorService AService BService CCentral controller directs each stepService XService YService ZeventeventeventServices react to each other's events Comparison Table Aspect Orchestration Choreography Control flow A central orchestrator explicitly invokes and sequences each step Each service reacts to events independently; no component sequences the whole flow Coupling Services couple to the orchestrator’s contract, not to each other Services couple to shared event schemas rather than a controller Workflow knowledge Orchestrator holds the full picture; services only know their own task No single component knows the entire workflow, only its trigger and reaction Failure handling Retries and compensation logic live centrally in the orchestrator Compensation is distributed, with services reacting to failure events themselves Adding new steps Requires modifying the orchestrator to include the new call A new service just subscribes to existing events with no central change Observability Single place to trace and inspect current workflow state Requires aggregating distributed logs and traces across services Failure/scaling risk Orchestrator can become a bottleneck or single point of failure Overall flow becomes hard to see, risking uncoordinated ’event sprawl' Typical tooling BPMN engines, AWS Step Functions, Temporal, Camunda Message brokers and event buses like Kafka, SNS/SQS, domain events Key Differences Orchestration uses a central controller; choreography relies on services reacting to events Orchestration couples services to the controller; choreography couples them to event contracts Extending orchestration means updating the orchestrator; extending choreography just means subscribing to events Orchestration gives centralized visibility; choreography requires distributed tracing to see the full flow Orchestration risks a bottleneck at the controller; choreography risks workflow sprawl across services When to Use Each Orchestration ...