Cloud Migration Strategies: The “6 Rs” and a Safer Path for Mainframe & IBM i

The benefits of the cloud aren’t a secret. It’s no longer cutting-edge, little-known technology. However, for many businesses cloud migration—the movement of business-critical applications from on-premises to the cloud environment—is still very much a going concern. 

Migrating legacy systems or modernizing them to make the most of the cloud can be a complex undertaking. That’s why it’s crucial to understand the different cloud migration strategies available, and which may best suit you. 

Cloud migration strategies: Key takeaways

• Cloud migration is the process of moving business applications and systems from on-premises to cloud infrastructure. It’s often a key part of cloud modernization, which also involves adapting the systems to the cloud environment.
• There are six principle types of cloud migration strategy, known as the “six Rs”; rehosting, replatforming, repurchasing, retaining, retiring, and refactoring.
• Benefits of cloud migration include cost optimization, flexibility, scalability, and security. 
• Insufficient strategizing and misjudgment of migration complexity are two of the main challenges that can hamstring cloud migration. 
• OpenLegacy can help enterprises to enact the correct cloud migration strategy in the way—and with the timeframe—that best suits them.

What is a cloud migration strategy?

A cloud migration strategy is the overarching plan an enterprise has for moving applications and systems from on-premises infrastructure to the cloud. Migration strategies are often a crucial part of an organization’s overall digital transformation efforts, and can include one or more of the most common types of cloud migration.

Different types of cloud migration: The 6 Rs of cloud migration

There are six main types of cloud application migration, all of them with different use cases, pros, and cons. 

Here’s a simple explanation of each of the types of cloud migration strategies to help you understand them better:

1. Rehost

Rehosting is the quickest and simplest cloud data migration strategy. Also known as “lift and shift”, it involves lifting data assets from on-premises systems and shifting them to the target cloud environment without making any code-level modifications.

As rehosting transfers data without adapting it for the cloud environment, it doesn’t support every cloud feature. However, the approach is still popular with enterprises that wish to perform large-scale migrations as well as businesses that just want to dip their toe into cloud modernization.

2. Replatform

The next step up from lifting and shifting is a replatforming strategy, which “lifts, tinkers, and shifts”.

After extracting the application from the on-premises system, some basic-level configurational changes are made before the app is transferred to the cloud. While the core architecture remains unaltered, these basic changes optimize the application’s performance for a cloud environment.

Businesses often use this legacy to cloud migration strategy as a stepping stone in modernizing complex core applications.

3. Repurchase

Known as the “drop and shop” strategy, repurchasing involves completely deserting your on-premises application and replacing it with a new, cloud-native version. This method is generally used to replace an on-premises application for standard functions (such as a CRM, accounting system, or CMS) with a Software as a Service (SaaS) solution.

Repurchasing grants you instant access to cloud application features and functionalities but requires your team to master completely new technology, which can be difficult. Furthermore, if you’re leaving a highly customized legacy solution, you may be disappointed if your SaaS solution lacks customizability.

4. Retain

For some applications, cloud migration just doesn’t make sense. Maybe they work perfectly in their original environment or are too complex to move without causing major disruption. Migration could also conflict with data compliance responsibilities.

In these situations, it is best to retain the applications in their existing environment and revisit migration at a later date.

5. Retire

As you evaluate your organization’s IT portfolio, there’s also a chance you’ll come across applications that are no longer useful. The solution here is simple—just switch them off.

This can generate impressive cost savings and refocus your productivity in other critical business areas. A word of warning though; remember to look out for any hidden dependencies before you retire an app.

6. Refactor

Refactoring—or rearchitecting—is the most complex and resource-intensive strategy on this list, but it can also unlock the most potential for growth.

Refactoring involves completely rebuilding an application from the ground up, essentially writing cloud-native functionalities into its core. As a result, you can leverage in-demand cloud capabilities such as serverless computing, auto-scaling, and microservices architecture.

Of all the cloud migration strategies, refactoring yields the greatest agility, resilience, and return on investment (ROI).

Cloud migration strategy example

Let’s take a look at one simple hypothetical cloud migration strategy example to demonstrate how this can look in practice:

• A manufacturing company has relied on an on-premises enterprise resource planning (ERP) solution since its foundation.
• They now find that solution limiting and are looking for something that can more easily integrate with the rest of their tech stack and make the most of the cloud environment.
• Weighing up the pros and cons of the different cloud migration strategies, the company opts for repurchasing. 
• They sunset their on-premises solution and invest in a cloud-based ERP alternative, benefiting from the expertise of the provider to help them with the transition. 

Why businesses need cloud migration solutions

Relying on outdated legacy systems to perform business-critical operations can put companies at a significant—even fatal—disadvantage. Not only are these systems difficult to upgrade and maintain, but they lack the flexibility and powerful functionalities that drive operational efficiency and customer-centered innovation.

The solution? Cloud modernization, which will generally include but not be limited to, cloud migration.

Cloud modernization aims to maximize the value of business infrastructure, systems, and applications by combining them with the rich capabilities provided by the cloud.

Cloud migration is an aspect of this. Using a variety of migration methods, you can leverage cutting-edge technologies and functionalities to strengthen your competitive resilience in a dynamic and disruptive commercial landscape.

With an effective cloud migration strategy, forward-thinking companies can unlock an abundance of benefits.

Benefits of cloud migration

It’s possible for businesses to achieve far-reaching, industry-specific cloud migration benefits. These are some of the most universal advantages that small, medium, and large enterprises can expect:

Cost optimization

Using cloud applications significantly lowers a company’s operational costs. Typically, providers offer subscription billing, which means you only pay for what you use and can optimize your cloud spend.

Additionally, as cloud providers host, maintain, and upgrade these applications, you significantly reduce infrastructure, labor, and maintenance costs for your business.

Scalability

Scaling a legacy system involves anticipating growth and pre-emptively purchasing and installing expensive infrastructure. Failure to accurately anticipate the scale of your expansion can result in wasted business productivity, money, and resources.

Cloud applications are inherently scalable, allowing you to easily add or remove resources in alignment with your business’s fluctuating needs.

Flexibility

Cloud migrations remove IT operations from data centers and unchain office workers from their desks. With everything stored in the cloud, your workforce can access networks and data from any location and any internet-connected device (even their smartphones).

The cloud also facilitates remote communications that enhance work-from-home capabilities. Thanks to the cloud and its many flexible capabilities, employees at opposite ends of the world can video call, share files, and collaborate on projects in real-time.

Security and compliance

When cloud migration is implemented with the necessary stringent security and compliance measures in place, it can provide greater protection than traditional data centers.

Cloud services typically offer in-built, enterprise-grade security features that align with regulatory compliance. This protects your network and data from threats, minimizing the risk of data breaches or data loss as well as the financial and reputational repercussions they can cause.

Cloud migration challenges

As with any significant technological endeavor, cloud migration is not without its challenges. Here are some key ones that it’s crucial to be aware of, in order to mitigate their impacts:

Insufficient strategizing

No cloud migration strategy can be successful without diligent design and planning. All too often, businesses jump into migration initiatives before they’ve devised a fully developed strategy.

Migrating legacy databases and applications must be considered on a case-by-case basis. Legacy systems can have different requirements, which affect which type of cloud migration approach is the best choice.

Understanding the intricacies of your current infrastructure, your target cloud environment, and the optimal use cases for each migration method allows you to create a successful end-to-end cloud migration plan.

Lack of cost optimization

In some cases, the upfront and long-term costs of cloud migration may climb higher than anticipated. This is usually the result of insufficient research into the hidden costs of migration, which can include upskilling, labor, infrastructure transformation, data loss and recovery, and more.

However, even the overt costs of cloud migration can financially overwhelm businesses that lack infrastructure visibility. This is why it’s important to conduct comprehensive pre-migration research, assessments, and planning. After all, managing cloud spend was the top challenge of migration cited by 84% of respondents in a recent survey.

Migration complexity

Businesses with complex IT architecture will also need to conduct large-scale analyses into their hardware, network, and app dependencies to combat potential interoperability and compatibility issues. The vaster and more complex your architecture, the harder this is to do. 

Companies may also need to execute different migration strategies for different applications. These must be executed in carefully planned phases. Underestimating the complexity of cloud migration can cause data loss, downtime, and other disruptions that impair business operations and customer satisfaction.

Businesses with more complex legacy systems can enlist the help of cloud migration service providers or integration platforms like OpenLegacy to simplify and automate the cloud migration process.

Cloud migration planning: Beyond simply migrating apps to the cloud

A comprehensive cloud migration plan will help you avoid common challenges and increase the speed, cost, and effectiveness of the process.

Here are the main things you’ll need to do before you begin:

Select the right cloud migration strategy

Each cloud migration approach has its unique benefits, limitations, and optimal use cases. They should be considered on an application-by-application basis in alignment with your business’s needs and capabilities.

Start by identifying your goals and objectives for cloud migration. These might include modernization, accelerated time-to-market, cost-savings, performance improvements, flexibility, or scalability. Your cloud migration methods should be influenced by your goals. For example, if you want to reduce costs, opt for a cheaper cloud provider.

Another influential aspect is your desired migration model, i.e. whether you want to use an Infrastructure as a Service (IaaS), Software as a Service (SaaS), or Platform as a Service (PaaS) solution. For example, if you wish to relinquish some control of your applications to reduce workload, you might move to a SaaS platform (repurchase).

The individual needs of each workload as well as the current capabilities and limitations of your organization are other important factors to consider when assessing cloud migration approaches.

A SWOT analysis to understand the strengths, weaknesses, opportunities, and threats that will govern your strategy can be a good starting point.

Identify infrastructure resources

Not only will you need to perform an initial, organization-wide cloud migration assessment to understand which on-prem infrastructures will benefit from migration, but you’ll also have to identify the resources required to deploy cloud migration and operate and maintain cloud services on a long-term basis.

For example, it’s likely you’ll need to upgrade your networking infrastructure. Allocating network resources appropriately is essential for meeting the bandwidth-heavy requirements of cloud-hosted applications and reducing the risk of latency or poor user/customer experiences.

Ensure cloud migration security

Data protection frameworks and security best practices should be intricately detailed before you even enter the testing stage. During planning, identify potential security risks and how these can be mitigated.

Here are some cloud migration security considerations to implement before, during, and after migration:

• Data compliance. Align security implementations with common data protection laws, such as GDPR and CPRA, as well as industry requirements, for example, HIPPA for healthcare or GLBA for finance.
• Strict access controls and user permissions. To prevent unauthorized access, strictly define who can access specific data and what they can do with it across cloud environments.
• Automation. To successfully adapt and scale security across complex and evolving cloud environments, businesses need to rely on AI and automation. You can infuse this into your cloud environment with specialized cybersecurity tools and APIs created by cloud providers to streamline security at scale.
• Machine learning. In the same vein as automation, machine learning plays a critical role in securing and maintaining large-scale cloud environments. With the ability to analyze large volumes of raw data, it can uncover potential vulnerabilities and rapidly alert you to suspected security threats.
• Robust data encryption. Implementing end-to-end data encryption (both in transit and at rest) is a must to prevent cybersecurity threats. The standard encryption protocol for data transmitted over the internet is Transport Layer Security.

Budget your cloud migration costs

Your cloud migration budget will need to include the cost of the initial migration as well as the ongoing costs of maintaining and scaling a cloud environment.

Start by calculating the current cost of every application you wish to migrate to the cloud. This should include administration, operational, and maintenance overheads.

Next, evaluate how much it will cost to migrate workloads to the cloud and run applications in your chosen environments. You can use cloud cost calculators to generate reliable estimates.

The more you work on this now, the fewer financial issues you’ll run into later.  

Be warned, a number of factors will influence costs, so be as comprehensive and realistic as possible. Make sure to include things like:

• Data volumes and storage requirements
• Optimal performance requirements
• Computing resources
• Cloud provider costs
• Networking requirements
• Outsourcing
• Training and labor

Map your migration

The next step is to create a roadmap detailing how your cloud migration process will be executed from beginning to end. Establish which applications will be migrated, when they will be migrated, and the specific strategy you’ll use to migrate them. Determine where the app will be positioned within the cloud environment and confirm any security or compliance requirements.

To reduce the risks of cloud migration, execute a phased or hybrid integration rather than a mass migration approach. Start with high-priority, low-risk applications to test the water before moving on to more complex migrations.

Perform pre-migration testing

Misconfigurations, poor performance, data loss, and other issues can all arise when cloud migration goes wrong. To prevent this, perform pre-migration testing in a safe environment to verify effective and optimized data transfer, synchronization, security controls, performance, costs, and migration time.

Any inefficiencies or problems you note should be resolved before you move on to the real migration process.

Where OpenLegacy fits into your cloud migration strategy

As the cloud environment continues to expand and evolve, so do the complexities of cloud migration. How, then, can you ensure that your enterprise is getting the most out of cloud applications and capabilities, without losing the benefits of existing legacy systems?

Regardless of whether you’re modernizing in place, shifting an application to a new platform, or carrying out a complete redesign, OpenLegacy can help simplify and automate your cloud migration.

Traditionally, you’d have to test an application in silos and only onboard users once it was fully set up. However, with OpenLegacy’s hybrid integration platform, you can create integration points that allow users to access the legacy system via the new functionality while you’re still working on it. This maximizes agility while enabling you to iteratively adjust your strategy.

There’s more to it than that, of course. OpenLegacy builds bridges between your on-premises systems and target cloud environments. From eliminating middleware to automatically producing digital-ready code, its core-to-cloud approach optimizes the time, cost, and complexity of your migration journey.

Legacy-heavy cloud migration: Mainframe & IBM i realities 

Three practical realities often missed in generic cloud guides:

• Stateful transactions: CICS/IMS units of work and IBM i commitment control require transactional integrity and rollback; many cloud patterns assume stateless REST calls.
• Protocol & data gaps: 3270/5250 screens, MQ/CTG/IMS Connect, COBOL/RPG program interfaces, copybooks, EBCDIC/packed decimals, and Db2 for z/OS data types aren’t first-class in typical tooling.
• Performance, security & governance: Throughput/back-pressure, RACF/ACF2 authorization, MFA, audit trails, and residency demand specialized gateways and patterns.

A modernization-first playbook: Decouple, coexist, migrate 

• Identify a decoupling boundary (domain, transaction, or dataset) and expose it safely as APIs.
• Run in coexistence: keep UIs and operations online while you redirect traffic gradually and monitor service levels.
• Migrate at your pace, with controlled cutovers and structured rollback; retire technical debt wave-by-wave.

Decoupling patterns you can mix & match

• Internal Decoupling: Replace internal program calls with secure remote APIs so refactored modules can still call what remains on mainframe/IBM i—no downtime.
• External Decoupling: Keep channels unchanged (e.g., 3270/5250, gateways); route to cloud services behind the scenes while modernizing the core.
• Data-Layer Decoupling: Extract/replace embedded SQL with data APIs; support hybrid reads/writes during migration (with CDC).
• Logic-Layer Decoupling: Separate business logic from legacy screens and expose as reusable services.
• CDC/Data Sync: Synchronize legacy and modern datastores to enable low-risk cutovers.

OpenLegacy is the modernization enablement platform that eliminates risk from legacy-to-cloud transformation. We don’t rehost, refactor, or rewrite your applications — we ensure that whatever modernization path you take, your legacy and modern systems coexist seamlessly. With OpenLegacy, you modernize at your pace, without disruption.

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

Next steps: Explore decoupling patterns and phased modernization in OpenLegacy Hub.

Cloud migration strategies FAQs

How do you migrate an application to the cloud?

How you migrate an application to the cloud will depend on the application and your business needs and goals. In general, there are six options; rehosting, replatforming, repurchasing, retaining, retiring, and refactoring.

What protocols are used during migration to the cloud?

To ensure the security of your data during cloud migration, you can encrypt it using secure protocols like HTTP and TLS. These provide end-to-end encryption. Remember to always encrypt data when it’s being transferred across locations (in transit) as well as when it’s stored in place (at rest).

What’s the difference between cloud migration and transformation?

Both concepts involve the transfer of data and applications to the cloud, but cloud transformation and migration are two very different things.

Cloud transformation is a large-scale digital modernization initiative that involves all your on-premises infrastructure being migrated to the cloud. Your processes, data, and applications must all be redesigned, rebuilt, or optimized for the new cloud environment.

Cloud migration is a singular (but critical) phase in the process of cloud transformation. It involves moving data and applications from on-premises to cloud-based servers, whether that be through “lifting and shifting”, “dropping and shopping”, or any other cloud migration method.

You can perform cloud migration without committing to a complete cloud transformation by choosing to only move some of your applications or opting to integrate your legacy systems with cloud solutions.

Did Netflix move to the cloud?

Yes—Netflix officially became cloud-native way back in 2016 (after seven years of cloud transformation).

Their decision to move to the cloud was made in 2008 after a combination of data corruption and unprecedented business growth led them to search for a secure and scalable alternative to their physical data center.

They migrated to Amazon Web Services cloud (AWS) and never looked back.