Technical Debt - How Legacy Systems Are Created

Introduction

Technical debt is a major factor in how legacy systems are created.
It doesn't happen overnight. It accumulates over time.

If technical debt is neglected for a long time, even small changes become risky. A once easy system becomes one that teams are afraid to touch.

Technical Debt

Technical debt is one of the fastest ways for a healthy system to become difficult to maintain.
To understand how legacy systems are created, we first need to answer a few questions.

Technical Debt - What is it?

Technical debt is the accumulation of compromises made during software development that make future changes more difficult. Several compromises can eventually lead to technical debt.

Some of them are:

• Deadlines: Rushing through development to hit the deadline can lead to poor architecture design and implementation.

• Shortcuts: When the timeline for development is short, or when the deadline is close, shortcuts become a necessary evil. That usually leads to technical debt in the background.

• Poor documentation: Missing or poor documentation of the application will lead to a lot of technical debt in the future.

And much more, which I will try to cover in this article.

Technical Debt - Why does it happen?

There are several reasons which makes technical debt accumulate in a project, so why does it happen?
Let's explore these reasons in more detail and understand why they happen in a project.

• Deadlines: Rushing through development does lead to technical debt, but sometimes it's unavoidable.

Why do deadlines cause an issue? Can we push them back to avoid technical debt? Yes, but not always.
It mainly depends on the organization that's working on the project. Different entities can set a deadline, and the higher they are on the organization ladder, the harder it is to push the deadline back.

A deadline set by a Project Manager could be pushed back if they allow it.
A deadline set by a Stakeholder would be harder to push back.
A deadline set by a Governing body would be almost impossible to push back without risking financial costs or penalties.

A tight deadline leads to rushed development and poor architecture design. If the deadline is too tight, architecture design can even be neglected, and development starts immediately.

You will meet the deadline but risk a lot of technical debt that you need to resolve later.

• Shortcuts: Shortcuts are usually a choice to be made. Can you afford the time to stop and properly design the system architecture to be scalable in the future, or do you need to hit the deadline and gain financial profits earlier?

Sometimes they're unavoidable because of a tight deadline. And sometimes they're necessary because of a change in requirements unless you're prepared to spend time refactoring and redoing most of the work that was already done for a small change so it keeps up with the architecture that was designed in the first place.

• Poor documentation: Not everyone understands the importance of good documentation until it's too late.

You can design the perfect system, the perfect feature, and it works perfectly in production. It's left untouched for months until something suddenly breaks or requirements change.
Even if the original developer is still on the team, they may not remember every decision, assumption, or workaround months later. If someone else has to do the work, understanding the system becomes even harder.

At that point, the value of good documentation becomes very clear.

Development
           ↓
No documentation
           ↓
Requirements change
           ↓
Knowledge is lost
           ↓
Assumptions are made
           ↓
Workarounds instead of proper changes
           ↓
Technical debt

• Lack of experience: Experience can contribute to technical debt when teams don't have enough guidance to make good architectural and technical decisions.

A team may be composed of junior or mid-level developers without experienced engineers to review designs, challenge assumptions, and provide technical guidance. As a result, decisions that solve today's problem may introduce unnecessary complexity or make future changes more difficult.

If the team is not well equipped to handle the complexity of the project, the implementation may become difficult to maintain and scale over time. Small changes require more effort, encouraging more workarounds and shortcuts to meet deadlines, which increase technical debt.

Does that mean junior or mid-level developers equal technical debt? No.

• Changing requirements and business pressure: Changing requirements are a normal part of software development. Business priorities change, and new opportunities appear.

On their own, changing requirements do not create technical debt. The problem starts when those changes are expected to be implemented without adjusting the timeline or scope of the project. As the pressure to deliver increases, developers are encouraged to introduce workarounds and shortcuts to keep delivering features quickly.

Over time, temporary solutions become permanent ones. What was intended as a quick fix becomes another layer of the technical debt that makes future changes more difficult.

Technical Debt - How does it accumulate?

Technical debt is not always a bad decision. The problem is not taking on technical debt.
The problem is that when technical debt is neglected and never repaid.

Legacy systems are not created overnight. Most legacy systems started as well-designed applications.
They became legacy because every compromise was considered temporary, but very few were ever revisited. The accumulation of technical debt over a long period of time can lead to their creation.

The accumulation of technical debt happens for several factors. Ideally, a software development project will have a pipeline for developing new features which should include some of the following stages:

• Business Requirements

• Technical Requirements

• UI / UX Design

• Architecture Design and Documentation

• Development

• Testing

• Verification

• Deployment

However, there are times when this pipeline is intentionally bypassed because of an urgent requirement or an exceptional circumstance.
The urgency pushes the boundaries of what is acceptable during the development pipeline and leads to introducing some of the technical debt factors that were mentioned in the previous section.

• Temporary Workaround

• Shortcut

• Lack of documentation

• Temporary workaround built on top of an earlier workaround

The last point is painfully funny, because I have seen it happen multiple times and it always leads to technical debt.

One more thing that is a factor in the accumulation of technical debt is visibility.
Technical debt is rarely visible to everyone. It's usually visible only to the people maintaining the system.
You see it, struggle with it, and probably hate it.

However, from a customer and business perspective, it does not exist. Not always.
The issue of visibility is what makes it hard to pay back the technical debt.

Why would you spend time fixing something that's not broken? Instead of working on something useful?

But it is broken. You just don't see it.

That's why documenting technical debt and its long-term effect on the product is very important.
It helps communicate the impact clearly and explain why the debt should be repaid.

Technical Debt - Warning signs

Technical debt is not always bad. Sometimes it's intentional.
Every system carries technical debt at some point. The important part is to understand which technical debt needs immediate attention and which can be kept for later.

• Slow Delivery: When the delivery of changes and features becomes slow because of technical debt.

Resolving this item becomes a priority. Otherwise, you risk incurring more technical debt that will further delay your delivery. Once the system becomes hard to manage and change the risk of critical issues increases without proper refactoring and paying back the debt you incurred.

• Frequent Production Incidents: When production incidents increase because of small changes to the system.

Technical debt increases the risk of critical issues, and once the system becomes unstable because of the amount of technical debt that was never repaid, that's the sign to start paying back.

• Limited Scalability: When the system cannot scale to handle the increased requirements and users.

Almost every system needs to be scalable. If the system incurred a lot of technical debt and the architecture did not support scalability, it becomes harder to scale the system without paying back the technical debt first.

• Fear of Change: When developers become afraid to modify certain parts of the application because every change risks breaking unrelated functionality.

Developers stop trusting the system because even small isolated changes can have unexpected side effects.
That's a clear sign of accumulated technical debt. At that point, repaying the debt becomes essential.

Technical Debt - How to reduce it?

You cannot fully eliminate the technical debt, but you can manage it properly so it doesn't become a problem. When managed and controlled properly, it becomes a benefit instead of a problem.

Taking on technical debt deliberately can speed up delivery when time is critical, provided there is a clear plan to repay it later. When controlled properly, it can speed up delivery and development.
But if ignored or not managed, it will become a liability.

Technical debt can be controlled and reduced if a proper process is implemented for it.

• Continuous Refactoring: Every developed system needs refactoring at some point in the future.

Knowledge increases with time, technologies change, and implementations become outdated.
Someone once said:

But if we work on it today to refactor, then we will have to refactor it again in a few years, right?

Well, yeah. You cannot leave a system as it is and keep adding features on top of it.
It needs to be refactored and enhanced over time. This is because of visibility that was mentioned in the previous section.

If you're a software developer, try going back to a codebase you wrote a few years ago. Would you still write the same code?

• Good Documentation: Create a process where everything is documented.

Not only are the solutions documented, but every important decision that was taken to reach that solution.
Keep a reference of them to avoid the difficulties of understanding the system and the assumptions that will be made about it in the future.

Documenting the technical debt is also important. You might be aware of the technical debt today.
But you might forget about it later. Keep a reference of the debt you have to pay later.

• Architecture and Code Review: Review is an important part of development.

Architecture review is as important as code review. A second pair of eyes validating the implementation can enhance it. It's important to understand that everyone makes mistakes or introduces bugs at some point.

The review phase is not to catch mistakes, but to enhance the system and implementations.

• Allocating Time: You can't manage and repay technical debt if the time is not allocated for it.

Technical debt accumulates quickly if there is not time to repay it.
You can control and manage the debt properly by reviewing and documenting everything. But if there's no time allocation to start repaying the debt, then it will never be repaid.

Thus, allocating time is an essential part of how you manage and control technical debt.

• Automated Testing: Refactoring without testing is risky.

Unit, Integration, and UI testing provide confidence that paying back technical debt doesn't introduce new issues. They allow developers to move forward with the necessary enhancements while reducing the risk of breaking existing functionality.

However, implementing and maintaining automated tests also requires time and effort. That investment should be considered during development planning and estimation.

Technical Debt - Is every legacy system bad?

A legacy system is not necessarily a bad system. Some of the most reliable systems in the world are considered legacy systems because they've been running successfully for decades.

The challenge is not their age. It's whether they can continue evolving safely.

If a legacy system is reliable and can continue evolving to support business needs safely, then it is not necessarily a bad system. The issue is when the system cannot continue as it is and it becomes essential to scale it. That's a difficult task to achieve, especially if there's a lack of documentation and the knowledge about it is outdated.

Conclusion

There's a misconception about legacy systems and technical debt.

Legacy System → Bad
Technical Debt → Bad

That's not the case.

Sometimes a legacy system works perfectly, and sometimes technical debt is the right choice for a problem.

In conclusion, it's important to understand:

• Legacy systems can be reliable, scalable, and continue evolving safely.

• Technical debt is not always bad, but sometimes it is.

Technical debt rarely becomes a problem overnight. It quietly accumulates through compromises, shortcuts, and temporary solutions until a once-healthy system becomes difficult to manage. Managing technical debt isn't about eliminating it.

It's about preventing today's compromises from becoming tomorrow's legacy.