COBOL Modernization: Your Complete Guide to Modernizing COBOL-Based Applications

Companies looking to update their legacy COBOL-based mainframe systems should consider a number of COBOL modernization approaches to find the best fit for their organization. 

While some may prefer to go down the minimally-disruptive rehosting route to preserve existing data models, others might opt for a rewriting approach to completely overhaul their system within a brand new cloud architecture. 

We’re going to look at why you should consider COBOL modernization, and the options that are available for achieving it successfully. We’ll also look at a few of the challenges you may encounter during the process, and how you can make sure these don’t disrupt your day-to-day operations.

COBOL modernization: Key takeaways

• COBOL is a well-established coding language that powers a wide variety of data-heavy applications, but wasn’t designed to integrate directly into modern architectures.
• Upgrading legacy COBOL mainframe applications can help streamline operations and reduce costs. Outcomes depend on workload design.
• You could choose to modernize in place, refactor existing code, or build a completely new solution, depending on your business goals and needs.
• To minimize the risk of downtime, use secure APIs and gateways to connect functions to modern architectures during a phased transition.

What is COBOL?

COBOL stands for COmmon Business-Oriented Language. It’s a programming language that was developed back in 1959 in response to the need for a common programming language that could be used across multiple business systems.

What made COBOL different in those relatively early days was its use of English words and phrases for coding rather than more arcane commands. This made it easier for non-experts to maintain the code, so it was ideal for businesses.

What is COBOL (still) used for?

Given how long ago COBOL was invented, you may be surprised to learn how widespread it still is, principally in mainframe applications. 

Its great strength is that it’s very good for handling large amounts of data efficiently. This means it’s still very common in legacy systems that need to process and manage large amounts of information, such as you might typically find in the finance sector, or complex administrative systems used by larger corporations. 

COBOL is particularly useful for helping users interact with structured data records and translating high-level source code into machine-readable code.

Bear in mind that many organizations that have been in business for many decades tend to have adapted existing systems over time rather than creating completely new ones as new tech has become available.

This makes sense from the point of view of avoiding operational disruption, since COBOL has been used to code core systems that can be pretty complex. No-one wants to dismantle such a system unless doing so is completely unavoidable.

That said, modernizing COBOL applications is becoming an ever more acute issue for many businesses as part of their mainframe modernization strategy. 

But why would such a strategy be necessary? After all, if it’s not broken, why fix it? Well, it turns out things aren’t quite that simple.

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Why should you consider COBOL modernization?

COBOL software modernization may be a good idea for a number of reasons. As time goes on, your business needs to adapt to the evolving digital environment, which means the technology you use has to remain up-to-date as well. 

Here are a few reasons you may want to consider COBOL modernization:

You need to integrate legacy applications with modern systems

When COBOL was first developed, the cloud didn’t exist. Nowadays, many businesses use cloud-based tools as a matter of course, and COBOL-based software isn’t set up for direct integration into cloud applications. 

In order to get legacy systems to communicate properly with modern tools, you need to find a way of integrating them.

You need more advanced features and capabilities

COBOL-based systems are reliable and robust, but there’s no doubt they’re beginning to show their age. If you want to deploy more advanced features and functionality, often the only option is using more modern applications.

Your workforce is lacking COBOL-specific expertise

Another factor that often pushes organizations to implement mainframe to cloud migration is that it can be difficult to access the required expertise. While COBOL specialists do exist, it’s not a skillset that’s common among today’s programmers, who usually specialize in more modern coding languages.

You want to cut operational costs

Businesses are sometimes pushed into adopting COBOL modernization platforms if the cost of maintaining their legacy system becomes prohibitive. Integrating old mainframes into modern solutions is usually pretty cost-effective over the long term.

You need to keep up with security, privacy, and regulatory requirements

The regulatory framework many businesses operate within is ever-changing, particularly in fields such as finance or healthcare. To stay compliant, it may be necessary to make crucial updates to existing systems and data processing procedures.

What are the main challenges in modernizing COBOL applications?

If you’re looking to modernize your mainframe COBOL-based applications, there are a number of issues you might encounter during the process. Here are some of the common challenges:

Complexity of the legacy codebase

Imagine if you’d started building a small house in 1959. Every few years, another builder comes along and adds another section however they see fit, in line with whatever it is they need at that moment. Eventually, you’d end up with a huge structure that’s both solid and slightly uneven-looking, because it was built ad hoc according to changing design trends.

That’s legacy code. Over time, multiple programmers with completely different coding styles contribute to it, meaning it ends up being extremely complex. Worse, making changes to COBOL code can sometimes have unexpected knock-on effects elsewhere in the system, so anyone working on it has to understand the system well before they tinker with it.

Limited documentation and access to skilled developers

A related issue is that early programmers weren’t always careful about drawing up comprehensive documentation, which can be a real headache for anyone coming to the code for the first time.

And, of course, we’ve already mentioned the key problem of being able to find programmers with expertise in COBOL, since it’s a fairly niche skill these days. While the modernization platforms and frameworks can mitigate this problem to a certain extent, finding someone with the skills to grapple with legacy code effectively can still be a challenge.

Risk of downtime and business disruption

Because COBOL-based legacy systems tend to be the foundation upon which core business operations are built, there’s a real risk of significant downtime happening during the modernization process.

Companies are obviously concerned about this, since it can potentially lead to considerable business disruption that hits the bottom line. That said, experienced modernization partners do focus on addressing this dilemma by offering a range of possible modernization solutions, so there’s usually a way of minimizing the effects.

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What are traditionally the best ways to modernize COBOL applications?

COBOL modernization services​ use a variety of approaches, depending on a company’s specific business and technological needs. These vary by scope and complexity, and today can incorporate the use of APIs or microservices to simplify the process.

The three traditionally most common approaches, though, are rewriting, refactoring, and replatforming/rehosting.

Rewriting

You could describe this as the “translation” option. In other words, you take the COBOL code and completely rewrite it in a modern programming language such as Java or C#.

As you can imagine, this is something of a nuclear option. It represents a complete overhaul of your existing systems, so it’s highly time-consuming and resource-hungry.

However, sometimes it’s the best choice, even if it’s disruptive to ongoing operations in the short term. If your existing systems are simply becoming impossible to maintain, a fresh start will mean you can do a full reset with a new system that’s fit for purpose.

Refactoring

In principle, refactoring is generally less disruptive but does present its own challenges. It involves tidying up and refining the existing code to make it more efficient and easier to maintain.

For example, the programmer may decide to optimize PERFORM statements or standardize data structures like COPYBOOKS across multiple programs.

The main drawback here is that it can take a long time to complete the project, depending on the complexity of the existing code.

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Replatforming or rehosting

Replatforming involves taking a COBOL application and moving it to a new infrastructure with minimal code changes. For that reason, it is a popular approach for cloud modernization projects.

Typically, COBOL modernization solutions that take the replatforming route will involve installing some new middleware or making changes to data access methods.

Replatforming is inherently less risky than rewriting or refactoring, and because it preserves the existing business logic and data models, it’s less disruptive overall.

Where OpenLegacy fits (capability snapshot)

OpenLegacy’s core mission is to equip you with everything you need to achieve effective digital transformation. That includes providing a range of the best COBOL modernization solution alternatives​.

Modernize in place with an API-driven refactoring strategy that maintains core functionality with minimal code changes, creating a seamless bridge between your legacy system and modern cloud-native architectures. 

Alternatively, take advantage of integration-ready APIs so you can benefit from the best of both worlds, following a hybrid replatforming approach that supports a phased transition.

Or, if you prefer a complete overhaul of your system, OpenLegacy supports you through the process of decommissioning your legacy mainframe and migrating all of your applications to a new cloud architecture. 

Every step of the way, OpenLegacy helps you keep your key business-critical operations running as you move to a new system that gets your organization ready to meet the technological demands of the future.

Modernization isn’t one-size-fits-all. For many mainframe estates, the fastest safe path is phased; decouple a boundary, run in coexistence, then migrate at your pace with rollback ready. 

A modernization-first approach—decouple → coexist → migrate—delivers value incrementally while managing risk.

Mainframe realities to account for  

• Stateful transactions: CICS/IMS units of work and batch windows require transactional integrity; designs that assume stateless calls can break invariants.
• Data & protocol gaps: Copybooks, EBCDIC/packed decimals, Db2 for z/OS types, 3270 flows, MQ/CTG/IMS Connect aren’t first-class in typical cloud tooling.
• Security, governance & performance: RACF/ACF2, MFA, audit, data residency, and throughput/back‑pressure require specialized gateways and patterns.

A coexistence phase keeping operations online while you redirect traffic gradually helps contain risk and preserves service levels.

Choosing the right path

• Analyze & plan: Map dependencies and identify safe decoupling points for phased modernization.
• Generate & standardize: Produce modernization‑ready APIs (no/low/full code) directly from legacy assets and copybooks.
• Coexist & cut over: Keep legacy and cloud in sync; shape traffic gradually; keep rollback ready.
• Avoid lock‑in: Direct connectivity to core systems reduces dependency on generic middleware and one‑size iPaaS.