Legacy Software: Burden or Valuable Heritage?

Legacy software is often dismissed as outdated, but what’s really behind it? What does it actually mean for software to be “legacy”? Is it automatically a bad thing? What challenges do these systems bring—and should you act immediately? This article explores the definition, challenges, and opportunities of legacy systems and outlines strategic approaches for dealing with them.

What is Legacy Software?

Legacy software refers to systems still in use but made difficult to adapt due to outdated technologies, architectures, or lack of maintenance. Age alone doesn’t make software “legacy.” Three factors are crucial:

• Business-critical function: The system is essential for operations.

• Technical rigidity: Old technologies or monolithic architectures make changes hard.

• Pressure to change: New requirements (like compliance or security) demand updates the system can’t efficiently support.

A practical example: A Java application running version 8 (end of life: 2030) with 500,000 lines of code, unchanged since 2012, is considered legacy—even if it works flawlessly.

Is Legacy Always Bad?

Not necessarily! Legacy systems often offer:

• Stability: Many run for decades without major issues. For example, IBM’s COBOL-based CICS platform has processed 30 billion transactions daily since 1968 without outages.

• Embedded business knowledge: These systems are tailored to a company’s needs and support critical processes, often containing valuable domain expertise.

• Familiarity and integration: Employees are efficient with these systems, and they are deeply woven into the IT landscape.

The Problems

• Security risks: Legacy systems are vulnerable to cyberattacks due to missing updates and outdated tech. The 2017 WannaCry attack hit many companies using old Windows versions.

• High maintenance costs: Specialized skills and old hardware are expensive to maintain. Companies spend millions annually on support and parts, tying up resources that could go to innovation.

• Limited flexibility: Monolithic legacy systems are hard to integrate with modern IT (cloud, APIs), leading to data silos and slow adaptation to change.

Why Do You Need Specialists?

• Obsolete frameworks: Many legacy systems use outdated frameworks (like Struts or old Spring versions) with poor documentation, requiring deep expertise.

• Lack of documentation: Changes were often made directly in code, making onboarding and modifications time-consuming and error-prone.

• Custom solutions: Proprietary code tailored to specific business needs is rarely standardized and hard to modernize.

Maintenance and Modernization

Legacy maintenance involves more than just code:

• Security updates: Often missing, requiring expensive support or custom patches.

• Integration with new tech: Cloud and database migrations are complex and resource-intensive.

• Compatibility fixes: Old systems may not work with new hardware or software, causing unexpected errors.

Updating to newer versions (e.g., Java 21) can reduce risks and improve performance but doesn’t solve fundamental architectural issues—monoliths remain monoliths.

How Common Are Legacy Systems?

On average, about 31% of all systems are considered legacy, with Java-based systems above average due to their historical use in many domains.

Language	Legacy Systems	Typical legacy indicators
Java	40-60%	Java 11 (72%), Spring 4.X
Python	12-15%	Python 3.7 (18%)
JavaScript	18-22%	AngularJS (54%), Node.js 17 LTS
PHP	30-50%	PHP < 7.4 (30%)
.NET	30-40%	.NET < 4.8

How Long Does Software Live?

Software lifespan depends on language and use case. For Java, distributions offer long-term support from 5 to 8 years.

Language	LTS Support
Java	5 to 8 years
Python	5 years
.NET	3 years
PHP	2 years

Modernization Strategies

Modernizing legacy systems is a balancing act between cost, stability, and innovation. Common strategies include:

1. Code migration: Gradually replace parts of the system (Strangler Fig pattern), start from scratch (Greenfield), or migrate data/settings (Brownfield).

2. Containerization: Move monoliths to Docker/Kubernetes or the cloud (“lift-and-shift”).

3. API wrapping: Expose old logic via modern APIs (REST/GraphQL) to make it accessible without full migration.

Legacy: Challenge or Opportunity?

Legacy systems aren’t necessarily a problem—they’re a challenge and often an opportunity. They form the backbone of many companies and contain valuable knowledge. With the right strategy—stepwise modernization, containerization, modular monoliths, and stable LTS versions—legacy can become a resource, not just a burden.

Legacy code isn’t automatically bad code. Often, systems are labeled “legacy” just because they’re not on the latest version, even if they work reliably. Ultimately, the value of code is its ability to adapt to new requirements. With the right approach, legacy systems can become valuable assets—sometimes, there’s more potential in the old than you think!

ℹ️ This post was created in collaboration with pep.digital GmbH. The content was produced as part of my professional work and is shared here with permission.