Legacy systems are the applications that have been deployed in your data center for decades without undergoing many changes. In a fast-changing technology environment, these systems get outdated and are challenging to maintain. Legacy systems are not only defined by their age but sometimes by their inability to meet growing business needs, due to the underlying architecture and technology.

Often, large enterprises deal with legacy applications to run crucial day-to-day business tasks. These legacy systems are spread across industries such as healthcare, finance, transportation, and supply chain industries, and so on. Companies have to spend heavily on maintenance and support of these systems, which warrants the need to architect legacy systems. Rearchitecting and modernizing legacy applications helps organizations to be more agile and innovative, and also optimizes cost and performance.

In this chapter, you will learn about challenges and issues with legacy applications, and techniques to rearchitect them. Rewriting complex legacy applications may pose an additional risk of business disruption, so you will learn about refactoring applications or considering the option to migrate into a more flexible infrastructure. The following major topics will be covered in this chapter:

• Learning the challenges of legacy systems
• Defining a strategy for system modernization
• Looking at legacy system modernization techniques
• Defining a cloud migration strategy for legacy systems

By the end of the chapter, you will have learned about various challenges and modernization drivers for legacy systems. You will learn various strategies and techniques for the modernization of legacy systems. As the public cloud is becoming a go-to strategy for many organizations, you will learn about cloud migration of legacy systems.