Event-driven architecture — when to use events vs direct calls

Deciding between direct calls or event-based communication. Wrong choice leads to tight coupling or debugging nightmares.

Direct calls when: synchronous response needed, operation must succeed, single consumer, simple flow. Events when: multiple consumers, producer shouldn't know consumers, async processing OK, need deployment decoupling. Start with direct calls, extract to events when you see multiple consumers. Don't pre-optimize.

Events decouple but add complexity: eventual consistency, ordering, debugging difficulty. Direct calls are simpler but create coupling. Right choice is situational.