Rearchitecting Legacy Systems

Today’s organizations are operating in a challenging environment. The pace of change is unprecedented. Regulators and institutions are imposing new reporting and security requirements, new technologies are disrupting consumers’ expectations and perceptions, and the ecosystem is constantly evolving as new players enter the market. As a result, organizations are redefining their business models to provide the customer focus, agility, and technology they need to attract talent, be competitive, and grow.

Application modernization has become a critical component of these new business models to set up dev/test environments rapidly, experiment with new ideas, and develop new products and services. In addition to eliminating the need to invest in expensive and cumbersome infrastructure, a new system enables innovation through a broad set of available technologies.

Legacy systems are applications that have been deployed in your data center...

Learning the challenges of legacy systems

A legacy application presents significant challenges for an organization. On the one hand, there are critical applications that an organization has used for decades. On the other hand, legacy applications hold back the organization’s pace of innovation.

End users are looking for the most modern, technologically advanced applications in a hugely competitive environment. All new features usually come with the latest software, and legacy applications limit your ability to add those features that benefit end users.

The following diagram shows some significant challenges that organizations face with legacy systems:

Figure 15.1: Challenges with a legacy system

Before we dive into the solution, it’s essential to understand the issues clearly. Let’s explore the challenges of legacy systems in more depth to understand them better.

Difficulty in keeping up with user demand

Customer focus is the key...

Defining a strategy for system modernization

Often, a legacy system gets left out of an enterprise’s overall digital strategy, and issues get addressed as needed. A reactive approach prevents organizations from executing overall system modernization and benefits.

If your legacy system has serious business challenges, such as security and compliance issues, or cannot address a business need, you can take a big-bang approach. In the big-bang method, you build a new system from scratch and shut down the old system. This approach is risky but addresses a business need that can be mitigated from the existing legacy system.

The other approach is a phased approach, where you upgrade one module at a time and keep running both the old and the new systems. A phased approach is less risky but takes a long time and may be more expensive, as you need to maintain both environments with increased network and infrastructure bandwidth.

Approaching your application portfolio, prioritizing...

Looking at legacy system modernization techniques

Per your existing application analysis, you can take various approaches to upgrade your legacy system. The most straightforward approach is migration and rehosting, where you don’t need to change the existing system. However, a simple migration may not solve the long-term problem or provide any benefits.

You can take a more complex approach, such as rearchitecting or redesigning the entire application if the system no longer meets business needs. The following diagram illustrates the impact of the various methods:

Figure 15.4: Legacy system modernization techniques

Let’s examine the various modernization techniques shown in the preceding diagram.

Encapsulation, rehosting, and replatforming

Encapsulation is the most straightforward approach. If the system is business-critical and needs to communicate with other applications running on the latest technology, you should use this approach. With encapsulation...

Defining a cloud migration strategy for legacy systems

As the cloud becomes increasingly popular, more organizations are looking to migrate to the cloud for their legacy application modernization needs. You learned about various cloud migration techniques in Chapter 3, Cloud Migration and Hybrid Cloud Architecture Design. The cloud allows you to scale your application while keeping costs low and helps you achieve desirable performance, high availability, and reliability while maintaining application security.

Cloud providers such as AWS, Microsoft Azure, and GCP provide many options that can help you modernize your system. For example, you can take a serverless approach to build a microservice using AWS Lambda and Amazon API Gateway, with Amazon DynamoDB as the backend.

In the previous section, we discussed various legacy system modernization techniques and their application in moving to the cloud. The flow illustrated in the following diagram will help you decide whether...

Mainframe migration with the public cloud

Many enterprises are moving their mainframe workloads to the cloud to take advantage of cost reduction, increased agility, technical debt reduction, digital strategy support, the legacy mainframe skills gap, and data analytics. Mainframe workloads are more challenging to migrate than x86-based workloads because legacy mainframe applications are often developed and deployed in a tightly coupled manner. For example, a mainframe application might include programs used by several subsystems or directly called by other applications. In these cases, changes made to the underlying programs also affect the associated subsystems and applications.

Transitioning from mainframe systems to the cloud presents a unique opportunity, even though cloud providers may not support the exact mainframe hardware architecture. For organizations, this transition involves strategic choices: they can emulate mainframe environments on x86 platforms or refactor their...

Modernizing legacy code with generative AI

Modernizing legacy code with GenAI represents a cutting-edge approach to software development. GenAI tools can analyze and understand legacy code, often written in outdated programming languages, and assist in rewriting or translating it into modern, more efficient languages or frameworks. This process accelerates code modernization and helps maintain the functionality of legacy systems while leveraging the advantages of current technologies.

By automating part of the code conversion process, genAI reduces the manual effort and expertise required, making the modernization process more accessible and less error-prone. This approach mainly benefits businesses looking to update their legacy systems without disrupting operational efficiency. Modernizing legacy code with GenAI involves tools like Codex, part of OpenAI’s offerings (which powers GitHub Copilot), and, potentially, foundation models. These tools leverage AI to understand...

Summary

In this chapter, you learned about the various challenges with legacy applications and why it is essential to modernize them. You learned about the benefits an organization can get by upgrading its application to the latest technology. Application modernization can be complicated and risky, but it is often worthwhile.

The outcome you get from the upgrade is a trade-off against the amount of investment and energy you put into it. Before defining the modernization approach, it’s essential to understand your legacy system thoroughly, and you learned about various assessment attributes of an application in technology, architecture, and code.

After the assessment, the next step is to define the modernization approach, and you learned about various modernization approaches, including architecture-driven, system re-engineering, and migration approaches. You also learned about multiple techniques for system modernization, including straightforward approaches (encapsulation...