Mainframe Applications Rehosting – Why Do It and How Does It Really Work?

Posted by Rick Fowler, TCC Director of Mainframe Managed Services

We have been hearing for years that mainframes are no longer viable platforms for modern computing, however over 70 percent of all financial transactions are still processed by a mainframe application. Durand, D. (2017, April 11). LzLabs: The art of mainframe application ‘re-hosting’. Retrieved from https://www.computerweekly.com/blog/CW-Developer-Network/The-art-of-mainframe-application-re-hosting. Therefore, the conversation has turned to modernization, rather than elimination of mainframe systems.

In an article titled “LzLabs: The Art of Mainframe Application ‘Rehosting’” in Computer Weekly magazine https://www.computerweekly.com/blog/CW-Developer-Network/The-art-of-mainframe-application-re-hosting the rehosting concept is broken down into straightforward stages and clear benefits are outlined.

The article states that the latest method of system migration may also be the fastest and most reliable because it occurs with no changes to application code. Changes to code can be risky, because they have not been as thoroughly tested as in the previous system.

The article breaks down re-hosting into three stages:

“1. Packing up all of the application artifacts in their executable form on the source system”

“2. Moving the package to the new platform”

“3. Unpack and run”

“In order to achieve this, the system services running on the mainframe subsystem must be re-written natively for Linux. This includes systems for transactional activity, batch scheduling, indexed datasets and relational and hierarchical data.”

“To paraphrase Carl Sagan; if you wish to faithfully recreate a mainframe environment to run on modern, open platforms, you must first invent the universe.”

“A translator may also be needed in order to transpose the mainframe binaries, based on the assembly language of the mainframe architecture, into Intel x86 Xeon assembly language, so that it can be used on Linux. This process is called “Dynamic Instruction Set Architecture Translation.” These transformed binaries are then able to run in a managed container.”

In a follow-up post, we will look at the tangible benefits of this approach.

To learn more about TCC’s Mainframe Managed Services please visit our website https://e-tcc.com/managed-services.