design-event-sourcing-cqrs

Designing an event-sourced architecture involves defining immutable, past-tense event schemas and aggregate boundaries. This treats business history as the primary source of truth, ensuring every state transition in your financial ledger is verifiable and replayable.

The best way to decouple read and write operations in CQRS is to separate write-side command processing from read-side projections. This allows independent scaling and optimized query performance while maintaining state consistency across complex domain models.

You need event sourcing for audit trails and temporal queries when building compliance-heavy systems or complex workflow state machines. It ensures a perfect audit trail by storing immutable history, allowing temporal state reconstruction for verification.

Handle schema evolution in event-sourced systems via upcasting and ensure idempotent projections to manage data consistency. This addresses common pitfalls like projection lag by decoupling write-side commands from read-side query updates.

CQRS supports optimistic concurrency by separating command processing from read models, ensuring state consistency in complex domain models. This prevents concurrent write conflicts while maintaining an immutable, replayable event history.