Mainframe migrations: how do you approach them?

Does your organization still rely on a mainframe and would you prefer to phase out? If so, it is essential to carefully plan this process to ensure that your systems continue to function throughout the migration. In this blog, we explain what to consider and outline several possible scenarios for a mainframe migration.

Why phase out your mainframe?

Phasing out a mainframe is an intensive process and not something you want to postpone for too long. Maintenance costs can be substantial, and it is becoming increasingly difficult to find developers with mainframe and COBOL expertise. As a result, making changes within a mainframe environment is often no longer feasible.

A mainframe is a textbook example of a classic monolith. Databases, user interfaces, business logic, and integrations all live in a tightly structured environment that no longer aligns with modern requirements. This makes it extremely difficult to achieve flexibility or modernize parts of the system. Over time, this creates a complex legacy challenge that can seriously limit the growth of your organization.

What should you consider when planning a mainframe migration?

Mainframes typically process data in batches, while modern organizations tend to be message driven. To gain flexibility, you often need to transition from batch processing to message-based communication.

In addition, functions in a mainframe environment are often used both internally and externally. This makes it difficult to move parts of the logic or data elsewhere, because they are still required by the internal application. External integrations frequently rely on mainframe-specific formats such as COBOL Copybook, which creates tight coupling between consuming systems and the mainframe.

An integration layer, such as the Frank!Framework, helps decouple systems and provides the flexibility to modify them independently.

How do you approach a mainframe migration?

There are multiple ways to carry out a mainframe migration. It is crucial to assess your specific situation carefully and perform a thorough analysis based on questions such as:

• What functions does the mainframe perform?
• Which connected systems are affected by phasing it out?
• Can parts of the system be separated and split up?
• Is tooling used to generate COBOL code, such as CoolGen?
• Where is the highest business value? Shutting down the machine entirely or introducing a more flexible system alongside it?

Converting COBOL code

One option is to convert COBOL code to another programming language. There are tools on the market that support this approach. The drawback is that converted code often still requires a runtime engine to function. In many cases, the interfaces remain based on COBOL Copybook formats. This means that only the programming language changes, while the system architecture and integrations remain largely the same. In this scenario, you mainly eliminate the need for mainframe hardware, but the underlying legacy remains.

The Strangler Fig method

With the Strangler Fig approach, you place an integration layer around the existing system and gradually redirect functionality from the outside. Step by step, you replace parts of the mainframe from within. This allows you to introduce alternative paths within the integration layer while continuing to use the existing hardware until the mainframe application is no longer needed.

Building a parallel system

Another approach is to build a new system alongside the mainframe and gradually replace it. Initially, data is synchronized between the new system and the mainframe. Over time, you shift ownership of the data entirely to the new system, reducing reliance on the mainframe until it can be fully retired.

Getting started with phasing out your mainframe

There are many ways to phase out a mainframe, and every approach comes with its own complexity. As integration specialists, we help organizations gain more flexibility when choosing migration scenarios. We are happy to review your specific situation, support you in creating a solid analysis, and ensure that your mainframe migration runs as smoothly as possible.

Feel free to contact us to discuss the options.

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