Enterprise Insurance Company
Migrating 2M+ Users from Legacy Java to a Modern TypeScript Stack with Zero Downtime
A Fortune 500 insurance company needed to migrate their legacy Java platform serving 2M+ users to a modern stack. Our team of 6 executed the migration with zero downtime and zero data loss.
2M+
Users migrated with zero downtime
65%
Reduction in infrastructure costs
87%
Test coverage (up from 12%)
The Challenge
The client operated a legacy Java EE platform built in 2009 that served their entire policyholder base of 2.1 million users. The system ran on aging on-premise infrastructure with manual deployments that took 3 days. The 400K+ lines of Java code had minimal test coverage (12%), and the team of 8 internal developers spent 70% of their time on maintenance and bug fixes rather than new features. Recruiting Java developers willing to work on the legacy codebase was proving nearly impossible, and the annual infrastructure costs were $2.4M. The board mandated a modernization within 18 months.
Our Solution
We provided a team of 6 — 2 senior TypeScript/React frontend engineers, 2 backend engineers (TypeScript/Node.js), 1 cloud architect (AWS), and 1 DevOps engineer — who embedded with the client's internal team. We adopted a strangler fig migration pattern, replacing modules incrementally while the legacy system continued running. The team built a modern React frontend with a design system, migrated backend services to TypeScript with comprehensive test suites (achieving 87% coverage), containerized everything with Docker and deployed to AWS ECS with Terraform, and implemented feature flags to enable zero-downtime switchovers for each module. Data migration was handled through a custom dual-write system that kept both platforms in sync during the 14-month transition period.
Tech Stack
"Migrating a 15-year-old platform serving 2 million users with zero downtime seemed impossible. Quo's team made it look routine. Their strangler fig approach let us modernize incrementally without ever putting our policyholders at risk. The $1.5M in annual infrastructure savings alone justified the entire project."
Michael Torres
VP of Engineering, Enterprise Insurance Company
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