Abstract

This systematic review examines application modernization strategies through the lens of modular and service-oriented design principles, exploring their effectiveness in contemporary software development. As organizations face the challenges of transitioning from legacy systems to more agile, scalable architectures, modernizing with modularization and service decomposition has emerged as a key strategy. The review synthesizes findings across a range of industries, including finance, healthcare, and government, identifying common modernization approaches such as rehosting, replatforming, and refactoring. It emphasizes the role of service-oriented architecture (SOA) and microservices in achieving greater system agility, scalability, and maintainability. The paper also discusses the evolving frameworks and models used in these transformations, such as the Strangler Fig Pattern and Gartner's Pace Layered Strategy, which facilitate the gradual evolution of legacy systems into modern platforms. The review offers practical implications for software developers, architects, and enterprise IT planners, suggesting avenues for future research, including the integration of artificial intelligence, domain-driven design, and cloud-native transformations in application modernization.