How do SOLID principles apply to event-driven architectures?

SOLID principles remain highly relevant in event-driven architectures (EDA). SRP: each event handler has one responsibility — process one event type. Avoid handlers that react to many unrelated events. OCP: adding new behavior to a system by publishing new event types or adding new subscribers, not modifying existing handlers. The event bus itself is closed for modification but open for extension via new subscriber registrations. LSP: events in the same hierarchy (e.g., OrderPlaced, OrderCancelled both extending OrderEvent) must be handleable by code written against the base type without special-casing. ISP: subscribers subscribe to specific event types, not a fat interface of all possible events. DIP: producers and consumers are decoupled through the event bus abstraction — neither knows about the other. Saga patterns and process managers in DDD apply SRP within complex event choreography.