In the refactoring approach, you can refactor your code to accommodate the new system. In refactoring, the overall architecture will be the same, yet you are upgrading your code to make it more suited for the latest version of the programming language and operating system. You can refactor the portion of code to apply automation and perform feature enhancement. You may want to take this approach if your technology is still relevant and able to accommodate business needs with code changes.

In the rearchitecting approach, you decide to change the system architecture by reutilizing the existing code as much as possible. For example, you want to create a microservices architecture out of your existing monolithic architecture. You can take one module at a time and convert it into a service-oriented architecture by giving each module a RESTful endpoint. The rearchitecting option helps you to achieve the desired scalability and reliability; however, overall performance results may be average due to the reutilization of existing code.