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Learn all you need to know about mainframe to cloud migration: why you need it, the challenges you might face, and options for mainframe modernization.


Mainframe to Cloud Migration: An In-Depth Guide

Posted by Angela Davis on November 22, 2023
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Mainframe architecture has served us well for more than half a century, but many forward-looking businesses are now opting for mainframe application modernization

To save space, money, and time, some consider migrating their legacy mainframe systems to the cloud. So, what does mainframe to cloud migration involve, and what benefits—and challenges—could it bring for businesses like yours?

Let’s take a look.

What do we mean by mainframe cloud migration?

In simple terms, mainframe cloud migration is exactly what it sounds like: Migrating mainframe applications, programs, and resources to the cloud.

Of course, nothing is as straightforward as it seems at first glance. In fact, rebuilding your mainframe in the cloud can be a complicated process, which requires a lot of planning, strategizing, research, and skill to accomplish successfully.

There are two broad methods for mainframe application migration:

  1. Moving the entire mainframe environment to a new, cloud-based hosting services provider.
  2. Refactoring mainframe applications to work on cloud-based platforms.

Within these two methods, there are various tools and tactics you can use to achieve your aims, and each have advantages and disadvantages. So, if you’re planning your mainframe to cloud journey, it’s a good idea to thoroughly research each of them.

We’ll go into strategies for putting your mainframe in the cloud a bit later. First, let’s take a look at why you might consider migrating.

The principal benefits of migrating a mainframe ecosystem to the cloud

Many of the major benefits of migrating legacy applications to the cloud apply when it comes to mainframe cloud migration, too. These include:

Simpler maintenance and reduced risk

Maintaining mainframes can be complicated, especially as your hardware ages. The mainframe owner is entirely responsible for this, meaning you have to manage everything from cybersecurity to updating programs and replacing old components.

Some people like the element of control this gives them over their mainframes. However, it can’t be denied that maintenance is costly and time-consuming. It takes a lot of resources, and making sure the mainframe is up to date is a constant (and often tiresome) task.

What’s more, there’s risk involved in sticking with legacy mainframes. It’s all too easy for cybersecurity measures to slip if you’re not constantly paying for newer and better security tools and features. Even if your security software is up to date, if your hardware gets too old, it may no longer be compatible with the latest updates.

Not to mention that a fault in the mainframe could wipe out all your data, or bring your operation to a grinding halt until you get things working again.

By migrating from mainframe to cloud systems, however, you eliminate much of the burden of maintenance and security. Your cloud provider will take on this responsibility and devote dedicated teams and resources to it. 

Improved agility and scalability

One of the reasons that mainframe migration is often considered by companies interested in legacy modernization is due to the agility and scalability of cloud systems. 

These give far more flexibility than rigid, monolithic mainframes. The nature of cloud architecture means that it has the capacity to scale both up and down as needed. 

This scalability allows business agility. Cloud systems can scale up and down on a day-to-day basis if required. For example, when workloads are high, a cloud system can expand its capacity. When they’re low, the same system can retreat and make sure you’re not wasting resources on capacity you don’t need.

All in all, cloud architecture provides the kind of agility and scalability that’s necessary in the fast-paced world of modern business.

Easier access to critical data

Cloud environments don’t only give secure options for data storage and management—they also offer multiple ways to securely access critical data.

A good cloud host will offer several interfaces for data management and analysis. This lets businesses access information more easily and get more from it than was possible with their old mainframe.

Additionally, cloud architecture is resilient and can maintain more applications for a lower cost than is usually possible in-house. This means companies can access more data with greater reliability whenever it’s needed.

Less reliance on mainframe experts

Cloud hosts also have dedicated teams whose entire job is to maintain, manage, update, and troubleshoot their cloud architecture. They have the resources needed to update their environments wholesale with the very latest tools and tech (as and when this is needed).

To get this kind of service with an in-house mainframe, you need to either be a mainframe expert yourself (and have access to the same resources as specialist cloud providers) or have professionals with the right skill sets within your organization. 

Unfortunately, professionals experienced in managing legacy mainframe systems are becoming fewer and farther between. Given the age of the technology, those professionals are increasingly retiring out of the workforce.

If you migrate your mainframe to the cloud, therefore, you mitigate that retirement skill gap. 

Typical strategies for mainframe application migration to the cloud

Now you know why migration from a mainframe to the cloud might be a good idea, let’s explore how it can be done. Mainframe application migration to the cloud generally involves one or more of the following:


Mainframe rehosting is a useful option if you want to migrate your system quickly. It essentially gives you a way to lift your legacy system from your mainframe wholesale, and run it from an open cloud environment.

This largely happens as a lift-and-shift operation, pulling applications from in-house data centers and moving them to a cloud host. 

There are several ways to achieve this, including mainframe as a service and using emulators, but the ultimate aim is always to lift the system as is and resituate it in a cloud environment.


Rebuilding/refactoring is more complex and time-consuming than rehosting; it’s also more transformative.

Rather than simply lifting your applications from one environment and copying them to another, a rebuild/refactor goes deeper. It involves rewriting part or all of an application to make it work perfectly within the cloud environment. 

This is a much lengthier process than rehosting, but the end result often makes it worth it. As the code has been specifically written to complement the cloud environment, rewritten applications are smoother to work with and less buggy than rehosted apps can be.


Sometimes, the best plan for mainframe modernization is to ditch the mainframe entirely and go for something completely new. In these cases, you might opt to retire your mainframe and set up a new system in the cloud.Retiring your mainframe is a big decision that shouldn’t be taken lightly. Before you retire and/or replace it, consider the following:

  • What would a new system provide that your mainframe does not?
  • Can you protect your essential data and transfer it from one system to another?
  • Have you consulted everyone whose work will be affected by this?
  • What do you stand to gain, and what do you stand to lose?

Choosing not to migrate

On the other hand, some may think why spend time and money fixing something that isn’t broken? While modernization is great, it may be that your mainframe is relatively new and fulfilling all your needs perfectly well.

There are various benefits to sticking with an in-house mainframe. This gives you control over your entire system and can help you cut costs if you know what you’re doing. 

So, if you’re confident in your management abilities and don’t have to modernize just yet, there may not be a need to migrate. You should keep in mind, however, that businesses always need to be thinking about the future, and not just the present.

Common mainframe to cloud migration challenges

We briefly mentioned some of the main mainframe to cloud migration challenges above. Now, let’s take a look at these in more detail.

Complex mainframe architecture

The more complex your mainframe architecture is, the harder it will be to migrate to the cloud. This is especially true if your system is heavily customized.

For example, there are protocols in place for migrating IBM systems to the cloud, because cloud developers expect to be working with IBM. However, if you’ve designed your mainframe yourself, you might have to work a bit harder to ensure it suits a cloud environment.

If you think your system is so complex that migration will be too costly and laborious to justify, there are other options available. For instance, you can keep your mainframe and update it, use specialized mainframe to cloud migration tools to help you, or retire it and opt for a new cloud-based system instead.

Data security risks during transfer

Ultimately, migrating your system to the cloud can be good for data protection, but during your migration, it’s important to consider security carefully.

Think about:

  • Where your data will be stored before transfer
  • How you’ll move data
  • Who’ll have access to data during your migration
  • How you’ll stay compliant with data regulations
  • How transferring/deleting data will impact data centers.

An insufficient migration strategy

A good strategy is key to successful mainframe to cloud migration, while a lack of planning can lead to all kinds of challenges.

Make sure you come up with a comprehensive strategy before you get started. Work out (in detail) what you want to achieve, the best system for you, the resources at your disposal, your chosen migration tactics, whether or not you need to undertake migration training, a timescale, and so on.A good, well thought-out plan can save you a lot of problems down the line.

Overcome mainframe to cloud migration challenges with OpenLegacy

Mainframe to cloud migration is a great way to modernize and future-proof your tech, but it’s not without its challenges. 

Luckily, OpenLegacy can give you another alternative with our innovative legacy API integration tech. With mainframe modernization via OpenLegacy Hub, you can seamlessly create APIs and microservices that cut out middleware and connect directly to your legacy mainframe system. This makes modernization much faster and easier.

Get in touch today, and learn more about how OpenLegacy can help you modernize your mainframe.

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