NorthBank: rebuilding the core in 9 months.
A fragile monolith handling $4B/year was holding back every product launch. We replaced it without missing a transaction.
0%
P95 latency reduction
0 mo
From kickoff to cutover
0
Customer-impacting incidents during migration
0
Engineers across both sides
The brief
NorthBank's core banking platform had grown organically over a decade — a single Java monolith, a single Postgres, and a queue system held together by goodwill. Every product change took six weeks of regression testing. The CTO wanted a clean slate without taking the bank offline.
What we did
Three engineers from our side, eight from theirs. Twelve weeks of architecture + greenfield work to get a parallel system up. Then a series of dual-write phases — every transaction landed in both the legacy and new system, with reconciliation jobs proving they matched. Cutover happened over a single weekend after four months of dual-write soak.
What changed
- P95 latency: down 73% (from 410ms to 110ms on the auth path).
- Deploy frequency: from monthly to multiple times per day.
- On-call pages: down 60% (from ~14/week to ~5/week).
- Time-to-launch: a typical product change went from six weeks of regression to two days.
It's the project that justified my hiring decision. Three engineers from Technology & SaaS demo did the work of fifteen.
Daniel K.
CTO, NorthBank
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