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Banking

API Integration Layer over Core Banking for Digital Channels

We built an API and integration layer that decouples mobile and internet banking from the core banking system. The bank now launches digital features without risky core changes, while protecting core performance.

Asia Pacific mid-market bank (composite) · Banking

API Integration Layer over Core Banking for Digital Channels

Challenge

Keeping balances accurate in the read store while offloading the core. We used CDC with sequence checks, cached reads with clear consistency rules, and kept all postings authoritative in the core.

Approach

We designed domain APIs (accounts, customers, transfers, cards, loans) exposed through an API gateway with OAuth2 and fine-grained consent. An integration layer translates to the core banking system's interfaces, with a CDC-fed read store (event-sourced projections) that serves balance and transaction queries without loading the core. New mobile app features are built on these APIs, and partner/open-banking APIs reuse the same layer with separate rate limits and monitoring.

Outcome

Illustratively ~50–70% reduction in read load on the core banking system Faster digital feature delivery without core release dependencies More stable performance during salary-day and month-end peaks Reusable APIs for partners and open banking Clear security and consent controls across channels

~50–70%Illustratively reduction in read load on the core banking system
✓Faster digital feature delivery without core release dependencies
✓More stable performance during salary-day and month-end peaks

Problem solved

Digital channels called the core directly, so every new feature risked core stability and month-end peaks caused slow or failed logins.

What we built

We designed domain APIs (accounts, customers, transfers, cards, loans) exposed through an API gateway with OAuth2 and fine-grained consent. An integration layer translates to the core banking system's interfaces, with a CDC-fed read store (event-sourced projections) that serves balance and transaction queries without loading the core. New mobile app features are built on these APIs, and partner/open-banking APIs reuse the same layer with separate rate limits and monitoring.

Benefits

Illustratively ~50–70% reduction in read load on the core banking system Faster digital feature delivery without core release dependencies More stable performance during salary-day and month-end peaks Reusable APIs for partners and open banking Clear security and consent controls across channels

API gatewayOAuth2CDCEvent-sourced projectionsOpen bankingConsent

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