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Legacy Software Re-engineering: Risks and Mitigations

It does not matter how well your current product is built if it is not supported by a well-designed software development process. Every software product becomes obsolete at some point in its lifetime and stakeholders have no option but to upgrade or discard it. 

New devices, software, and operating systems are being released all the time, creating an environment where old software no longer works as it did a few decades back. As a result, many businesses have turned to software modernization for the following reasons:

  • Cost – the costs of maintaining legacy software far outweigh its benefits.
  • People – an ever-growing workload on in-house engineers and a shortage of qualified specialists to keep an eye on outdated technologies means that more resources have to be spent on newer products.
  • Security – legacy code is easily vulnerable to cyber-attacks because it lacks security updates. Besides, old software may not comply with modern regulations.
  • New technologies – outdated technologies have limited flexibility to integrate with other technologies, making it harder or even impossible to customize the application and add new features.

When a business decides to modernize the software application, there can be three general approaches to solve the problem:

  • Move somewhere, for example, to the cloud or a new platform, or refactor some parts.
  • Change something in the codebase – this involves restructuring and cleaning up the code and or changing its architecture and programming language.
  • Change everything – a complete re-engineering of legacy software could mean having to rewrite the application from scratch.

In this article, we’ll focus on legacy application re-engineering, the pros and cons for enterprises, and how to create an effective and up-to-date re-engineering strategy.

What is Legacy Software Re-engineering?

Legacy software re-engineering is one of the effective software models to solve the legacy app issues and modernize the outdated code.

There seems to be no universal definition of what software reengineering is. Different authors imply various techniques when talking about re-engineering. Starting from the software maintenance automation and even all activities performed after the software implementation. In our opinion, the most relevant definition of the re-engineering process is understanding and changing a legacy system, and after that, reconstructing and implementing it in a new form.

Legacy System Re-engineering vs. Other Software Modernization Approaches

As mentioned earlier in the introduction, the software modernization problem can be solved in the following ways:

  • Move – migrate the application to the cloud or to a new platform.
  • Change something.
  • Change everything and rewrite the application.

Let’s explore each of the software modernization approaches in depth. 

Moving the application. This means moving the application “as-is” to a more modern environment. For example, from on-premises to cloud environments or moving to new hardware entirely. It is useful when the company resources are limited, and the code is relatively well-built. In most cases, when you need to migrate .NET Framework to .NET Core, the process involves well-defined steps without a total system makeover.     

Such an approach uses rehosting or replatforming techniques. Their main benefits are the following:

  • Minimal changes in the code,
  • No change in the core features,
  • Moderate resources and expertise are required to do everything promptly.

However, there are obvious disadvantages of the given approaches:

  • Migration may entail porting code errors and legacy components into the target system
  • The owner can’t adjust the software to its needs;
  • Can’t expand functionality on the go.

Changing everything. In comparison to legacy system re-engineering, this means software redevelopment – starting from rethinking business requirements, redocumenting, and even rewriting the application. This does not mean the whole application at once but incrementally throughout time. It can be useful for extremely problematic projects, in which there is no technical or business documentation, no original developers, and no robust software architecture. 

Differences between software re-engineering vs rehosting and replatforming | ModLogix

Such an approach uses rewriting and rebuilding techniques, or total replacing – using a third-party alternative product with utterly different infrastructure. As an example, it can be complex re-architecting of monolith systems to service-oriented architectural style. Oftentimes, organizations apply a split of these software modernization services to achieve better results.

Their main benefits are as follows:

  • Significant changes and introduction of new features,
  • Revision of project goals and business processes,
  • Future-proof solutions.

The challenges and pitfalls of changing everything in software are also substantial:


Changing something. Finally, we get to the bottom of things! Here’s where software reengineering comes to play. This approach concentrates on improving the technology itself either modifying the software architecture or the code structure and refactor problematic code pieces. It requires highly skilled engineers and a software architect for the project. 

Re-engineering of legacy systems is used when the codebase is far from perfect, and the team can justify the benefits of new technologies for the enterprise. This is probably the most common case with a vast variety of implementation techniques. Legacy software reengineering has the following main benefits:

  • Increased performance,
  • Code transparency and predictability,
  • Overall software enhancement,
  • Reduced maintenance costs.

What about the major drawbacks of this approach?  

  • Lack of documentation can lead to poor programming decisions,
  • Require a dedicated team that’s familiar with the system.

Legacy Software Re-engineering Process

Re-engineering legacy system includes three stages:

  1. Reverse engineering
  2. System transformation
  3. Forward engineering
Detailed software re-engineering process | ModLogix

What’s hidden inside this terminology?    

Reverse engineering (backward engineering or back engineering). This is the key point of software platform re-engineering, which is the understanding of the initial program. Depending on the nature of software properties to be discovered, reverse engineering performs a static or dynamic analysis.

  • During the static analysis, programmers examine the source code and create data structure representations.
  • The dynamic analysis is done during the code execution.

The result of reverse engineering is a set of abstract representations of the software system under consideration.

System transformation. This is the second stage of legacy software re-engineering. In the system transformation stage, the abstract representations obtained during the reverse engineering are further transformed into other representations at the same abstraction level. The aim is to improve the software structure, quality, and stability. The system transformation stage includes the following processes: refactoring, rearchitecting, and rewriting.

  • Refactoring – is restructuring the code at the level of methods and classes.
  • Rearchitecting – is refactoring at the level of modules and components.
  • Rewriting – is rearchitecting at the highest possible level.

Forward engineering. After system transformation, the transformed system representations can be used to generate physical implementations of the initial system – at a low abstraction level. Forward engineering starts with system specification and includes the design and implementation of a new system – like an ordinary software development process.

This step completes the re-engineering legacy application process where the renewed software meets the ultimate criteria of upgrading. 

When It’s Time to Re-engineer Your Legacy Software

Software re-engineering as one of legacy system modernization approaches is simple – not to rework the whole application while also being effective enough to improve the codebase. Consider re-engineering the software system in the following situations:

Three vital signs showing the time for software re-engineering | ModLogix

You want to save resources:

  • reduce the maintenance cost,
  • reduce the load on the qualified engineers,
  • save time – compared to redevelopment.

You want to clean up the codebase and remove the code “bad smells”, for example:

  • duplicate code
  • very long methods
  • not-needed generality
  • commented-out and expired code
  • dead and zombie code
  • non-testing and falling tests
  • null references and unnecessary mutable states.

You have ambitious future plans regarding your software:

  • switch to a modern technology
  • migrate to another platform
  • introduce new features
  • update the business logic

For example, AngularJS to Angular migration, that’s considered a platform upgrade entails rewriting and, subsequently, legacy software re-engineering services. Although these frameworks have common roots, their architectures have a world of differences. That’s why re-engineering the system is one of the most crucial steps to migrating to a reliable platform that we’ve described in our case study

Risks and Pitfalls of the Legacy Application Re-engineering and How to Mitigate Them

Software re-engineering is a complex task that has its risks and possible issues:

Development issues. Highly-skilled developers are required for this task. Initial developers have already switched to other projects or even left the company. However, the company typically has no money to hire new professionals and no time to teach the low or medium-skilled employees.

Management issues. Legacy software maintenance can stop being a top priority for businesses. In such a case, the top management loses interest in the software support, and it can be hard to justify the need to spend on updating the working code. Possible advantages are remote and not clear to stakeholders.

Cost risks. It can be hard to make exact cost predictions for the legacy re-engineering project due to a lack of expertise and documentation. It can become even more complicated because there is typically a need to expand the existing functionality, and at the same time, maintain compatibility with previous product versions.

Potential threats of changing environments. It is always risky to perform “live” changes in the working functionality – in real-time in production environments.

At ModLogix, a legacy software modernization company, we work with the whole spectrum of software modernization approaches, including application re-engineering. So far, our team knows all of the ins and outs of the re-engineering process, and we are eager to share our expertise in dealing with some of the most challenging projects.   

To mitigate the possible software re-engineering problems, we recommend the following preventive measures:

  • Try to gather the dev team with the senior architects and designers.

  • Make only minimum, necessary, and sufficient corrections and enhancements to the core logic.

  • Restructure the code and data to remove unnecessary complexity – to make the codebase manageable by the available human resources.

  • Perform code modifications step-by-step, not for the whole application at once. Select code parts for re-engineering thoroughly – only the most critical and less risky ones.

  • Automate everything that can be automated.

  • Document all the changes – not to generate a new legacy.

  • Communicate with all the parties involved in the re-engineering process – to clear the goals and available resources.

  • Report about the results as early as possible – to confirm the necessity of expended resources.

Final Thoughts

Software re-engineering helps to eliminate or at least reduce the inevitable legacy code risks, such as the departure of key developers, deeply-hidden bugs, server overload, overwhelming maintenance costs, and more. As with any methodology, it should be used carefully and adapted thoroughly to the particular application, its main tasks, and business processes.

Keep balance. Software improvements must not turn to ‘programming for the sake of programming‘. Don’t forget that the software works to solve users’ problems, but not to improve the development process itself, thus making it beautiful and convenient.

Keep calm and use force. Involve the team experience and prepare the dollar-based argumentation – to convince the business of the validity of the legacy software changes. Be consistent and patient, get ready to convert technical problems into measurable business metrics this way you can explain the necessity of long-term investments.

Speaking of the force. If there are any difficulties in preparing for legacy software re-engineering in your company, contact ModLogix professionals for a free consultation. We believe that there are no complex systems, but there are real experts who turn challenges into solutions.

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