Modernising a 220M-account retail bank to cloud-native in 18 months.
A European retail bank had already spent three years trying to replace its core in waves. We reset the program around domain-by-domain modernisation, an event backbone, and a managed cutover factory that could survive real regulatory scrutiny.
The situation we walked into.
The client carried 420 downstream applications on top of a 30-year-old core, with country-specific product logic hard-coded into nightly batches. Every prior migration attempt had stalled when finance, fraud, and servicing teams discovered a dependency too late.
We reframed the objective away from 'replace the core' and toward 'make product launches and resiliency materially better'. That let the bank sequence work by customer journeys, keep regulators informed with live evidence, and prove value before the final country cutover.
A simplified view of the delivery shape, the control points that mattered, and the signals the client team used to keep the program on track.
The changes that made the outcome possible.
Core decomposition
Deposits, cards, lending, and servicing were carved into independently releasable domains with shared policy services.
Event fabric
Kafka-backed canonical events replaced overnight file movement so risk, finance, and channels could subscribe in real time.
Cutover factory
Every rehearsal executed against the same runbooks, controls, rollback triggers, and executive command-centre dashboards.
Run transition
Managed services and SRE teams stood up 24x7 reliability coverage before the first production migration.
How the delivery moved from pilot to scaled operation.
Program reset
A single control tower, release calendar, and regulator-ready evidence pack replaced 17 local workstreams.
Foundations live
Deposits and onboarding domains launched behind APIs while the legacy core still handled settlement.
Dual-run scale-up
Cards, servicing, and customer messaging ran in parallel for six countries with automated reconciliation.
Country cutovers
Weekend migrations completed with rehearsed rollback points, war-room telemetry, and board-level dashboards.
What changed after the transformation settled into the run.
Product change moved from quarters to weeks
The retail product team can now ship rate, fee, and bundle changes through a governed API release path instead of core code freezes.
Run economics improved immediately
Legacy mainframe demand dropped, incident triage was automated, and the bank closed four expensive manual reconciliation towers.
Reliability became measurable
SLOs, golden signals, and resilience drills gave the COO the first real-time view of customer-impacting degradation across all markets.
The difference was not just better engineering. It was a delivery model that let compliance, operations, and product teams trust the move in real time.Group CIO - European retail bank