Event sourcing provides immutable audit trails and temporal queries. Learn how we implemented event sourcing to power our financial platform.
Key Takeaways
- Multi-tenant ledger architecture requires strong isolation between tenant data paths
- Event sourcing provides immutable audit trails critical for financial compliance
- Idempotency keys are non-negotiable for any payment processing system
- Horizontal scaling must not compromise ACID transaction guarantees
Introduction
Financial technology infrastructure demands a fundamentally different approach than typical web applications. The systems we build must handle not only massive throughput but also maintain strict consistency guarantees, comprehensive audit trails, and regulatory compliance across multiple jurisdictions.
Engineering Context
Key Concepts
Understanding the foundational concepts is critical before diving into implementation details. Financial systems operate under constraints that require careful consideration of consistency models, failure handling, and data integrity guarantees.
Every architectural decision in a financial system carries compounding effects. A choice made at the data layer propagates through the API surface, affects operational procedures, and ultimately determines what regulatory controls are feasible.
Architecture Overview
The architecture follows a layered approach with clear boundaries between the API gateway, business logic services, and the persistence layer. Each layer has specific responsibilities for validation, transformation, and durability guarantees.
Peak throughput across all tenants
Platform availability target
End-to-end processing time
Implementation
Implementation follows a phased approach, starting with core transaction processing and building outward to reporting, reconciliation, and real-time notification systems. Each phase includes comprehensive testing against production-like workloads.
System Decision
Decision
Why we avoided event sourcing for the hot path
Why
While event sourcing provides excellent auditability, the latency overhead for synchronous reads was unacceptable for real-time balance queries. We use event sourcing for the audit trail while maintaining materialized views for hot-path reads.
Trade-offs
- Increased storage cost from dual-write pattern
- Additional complexity in ensuring consistency between views
- Higher operational overhead for managing two data models
Impact
Reduced P95 latency from 450ms to 180ms on balance queries while maintaining full audit capability.
The best financial infrastructure is invisible to the end user but provides absolute certainty to every stakeholder in the transaction chain.— Engineering Team
Conclusion
Building financial infrastructure requires balancing competing demands: performance vs. consistency, flexibility vs. compliance, and speed of development vs. operational safety. The patterns described in this article have been validated across production workloads and represent our current best thinking on these tradeoffs.