Challenges of Migrating Monolithic Banking Systems to Microservices Architecture: A Case Study Approach

Modern banking systems increasingly rely on distributed payment infrastructures, yet many financial institutions continue to operate legacy monolithic architectures. This paper examines the practical challenges of migrating monolithic Spring Boot banking systems to microservices architecture, drawing from a real-world case study in the financial payments domain. We analyze a system comprising three independent payment processing modules — Visa ClickToPay, Visa Subscription Service, and Visa Concierge — which, despite their logical independence, share a common database and unified deployment pipeline. Our analysis identifies five core migration challenges: deployment dependency conflicts arising from inconsistent Java runtime environments, shared database coupling, inadequate test environment parity, performance bottlenecks under transaction load, and resource constraints in small development teams. We discuss how microservices principles, including containerization, database-per-service patterns, and independent deployment pipelines, can address these challenges. Our findings provide practical insights for small-scale financial institutions undertaking similar architectural transitions.