Types of cloud migration: advantages and disadvantages

Moving to the cloud can reduce costs, improve scalability, and create new opportunities for innovation. The challenge is that there is no single path to get there.

The main types of cloud migration include rehosting, replatforming, repurchasing, refactoring, re-architecting, rebuilding, and retiring or retaining applications. Each approach comes with different trade-offs in terms of cost, complexity, and long-term value.

Regardless of the approach you choose, organizations typically migrate to the cloud to achieve several key benefits:

• Decreased hosting, compute, database, networking, and administration costs: In the cloud, you no longer have to keep your physical servers running. On top of that, you no longer need to have a huge team of professionals supporting your on-premises infrastructure.
• Agility and scalability: Cloud-based services can scale to cope with fluctuations in user demand, while your teams can collaborate on projects and maintenance from anywhere.
• Disaster recovery: Cloud-based backup and recovery are more efficient, better maintained, and updated more regularly, making your operations more robust.
• Improved security: The cloud provider of your choice will take on a huge part of the security responsibility that was previously on your side, like the security of your infrastructure. It’s called the ‘shared responsibility model’.
• Reduced carbon footprint: Using aggregated cloud computing resources helps to reduce carbon dioxide usage, eliminating 1 billion tons of carbon emissions by 2024, as reported by the IDC.

While cloud migration offers significant benefits, the results depend on how the migration is executed. Organizations can migrate applications and workloads in different ways, each with its own impact on cost, complexity, performance, and operational efficiency.

Selecting the right approach early can help avoid unnecessary spending and reduce the risk of future rework. This guide explores the main types of cloud migration, their advantages and disadvantages, and the factors that can influence your decision.

A quick overview of application migration approaches

The right cloud migration approach depends on your organization’s goals, existing infrastructure, and cloud readiness. Some businesses prioritize speed and lower migration costs, while others focus on modernization, scalability, or access to cloud capabilities.

Before selecting a cloud strategy, it helps to assess your current environment. A review of your applications, architecture, dependencies, and potential migration risks can show which systems should be migrated, modernized, retained, or retired. Together, your business objectives and infrastructure landscape will shape your organization’s cloud migration journey.

After you’ve clearly outlined your cloud migration goals and assessed your current architecture, you can define your cloud strategy on your own or get expert help from cloud partners, like Avenga.

The most common cloud migration approaches are listed below, roughly in order of increasing complexity, investment, and technical effort. Understanding the advantages and disadvantages of each approach can help you choose the option that best fits your needs.

Rehost: Rehosting is often called “lift and shift” because you move an entire application from your internal servers and place it in the cloud without any changes.

Replatform: Your applications and data are migrated to a cloud platform, utilizing some of the PaaS services of the cloud platform (e.g., managed data stores or messaging middleware). The overall system architecture will remain the same.

Repurchase: In this type of migration, a new SaaS solution replaces the existing one.

Refactor: Using this approach, you partially or fully redesign and optimize an existing application to improve performance and reduce costs.

Re-architect: This type of migration takes refactoring to the next level. It includes an architectural redesign that takes advantage of both multi-cloud and native cloud environments.

Rebuild: This involves redeveloping an app or solution from scratch, entirely in the cloud, while taking advantage of the latest tools and frameworks.

Retire: Sometimes, a cloud migration plan will reveal which applications can be discontinued. Retiring an application requires data to be archived and cleaned up. An application can also be withdrawn when part of its functionality gets refactored, re-architected, rebuilt, or repurchased.

The pros and cons of different cloud migration approaches

Different cloud migration approaches have advantages and disadvantages and understanding what to expect from each type can help you adjust your migration strategy to your unique needs.

The rehost (lift and shift) approach

At this level of migration, your applications, data, and servers are moved to the IaaS tier of the cloud platform without major alterations. As a result, you continue to deal with servers, networking, and per-server maintenance, only utilizing virtual machines and networking services of the cloud provider. Except, you don’t take full advantage of the capabilities of the cloud. If you have an application located on a traditional server, you lift it along with all the necessary runtimes and software. You can either virtualize the bare-metal environment or migrate the existing virtual environment and then install the app within a virtual server, like Amazon EC2 or Azure Virtual Machine, and deploy the application within that.

Advantages: Rehosting is the cheapest and easiest way to migrate to the cloud. It requires minimum time and expertise and mitigates the risk of breaking anything by messing with your application’s code.

Disadvantages: Although rehosting is a comparatively simple approach, failures due to complex application dependencies or long outage periods might occur. If a virtual server goes down, your application goes down, similar to traditional server behavior. Additionally, even if a rehost cloud migration succeeds, you won’t be taking advantage of all the powerful cloud-native capabilities.

The re-platform approach

With re-platforming, you migrate the application from a traditional server, make configuration and environment-specific changes, such as containerization of the service, state offload, and distribution, session-management layer re-engineering, etc., and then migrate it to the cloud without modifying the application itself.

For example, say you have a legacy application running on a traditional server. You can re-platform and utilize the advantages of the new cloud PaaS infrastructure. Cloud architects can modify the way an application interacts with a database so it can take advantage of automation opportunities and a more varied database infrastructure.

In case you are moving an on-premises SQL database to a cloud-managed database, like AWS RDS (Relational Database Service), it may require a small number of changes that are usually limited to the application’s configuration. However, the wins are significant: the reduction of the operational burden, out-of-the-box mirroring and fault-tolerance, as well as other benefits.

Advantages: Replatforming doesn’t require a massive investment in time or money and several SaaS options provide re-platforming solutions. The re-platform approach allows you to improve a part of an application while the rest of the application remains operational in the cloud.

Disadvantages: Replatforming applications can sometimes get out of hand. It can vary from deploying just a few small changes to the application or service, up to a complete re-architecture of some components. Hence, replatforming might involve risks, such as errors in the code or configuration. You need to establish a thorough plan of which features you want to change beforehand and those changes should be very carefully implemented.

The repurchase approach

Repurchase means moving from purchased on-premises software to a cloud-based SaaS equivalent. For instance, transferring from CRM to Salesforce, or transfering the backend code that was hosted on premises to the private cloud data server.

Repurchasing software is a good option if you want to harness the scalability, flexibility, and agility capabilities offered by cloud solutions.

Advantages: Since the product you use is already configured for the cloud, you don’t need to spend time and effort configuring it yourself. More importantly, repurchasing can be cheaper than refactoring, as we’ll see next.

Disadvantages: Sometimes the repurchase approach can be more expensive than hosting the app or service on your premises. It also requires a high-speed bandwidth connection, and a poor connection can be the cause of potential downtime. What’s more, if your application is highly specialized and has unique features, repurchasing won’t be a viable option.

The refactor approach

Refactoring means re-engineering your application to become a cloud-native. For instance, you could migrate existing applications to virtual services or refactor relational and nonrelational databases into Amazon Aurora and Azure Cosmos DB.

The need to refactor is often induced by a business’ necessity that requires the need to add new functionalities and/or to easily scale up and down, which would be hardly achievable with the current service’s architecture.

Advantages: Refactored applications take advantage of cloud-native capabilities. From the long-term perspective, refactored software is much more cost-effective than a non-refactored app. They are quick, reusable, and allow on-demand provisioning.

Disadvantages: Refactoring has high initial costs and is time-consuming compared to other approaches.

The re-architect approach

Re-architecting optimizes an application and makes it more scalable, secure, accessible, fast and agile by modifying and extending its functionality. Such as, you could separate a monolithic application into many independent microservices that can be read, written, and executed independently.

Advantages: While the refactoring approach involves restructuring the code, the re-architect approach is about changing the way the code is functioning, thus capturing the value of the business advantages that are independent of the legacy codebase. Basically, re-architecting is refactoring at a higher level. Re-architecting means moving the service into a fresh paradigm, in the meantime reducing the specific parts of code.

Disadvantages: Re-architecting is even more time-consuming than refactoring and requires a higher amount of initial effort. The code re-architecting may be complicated to carry out, which can potentially lead to bugs or security issues as the changes will be deployed to production.

The rebuild approach

With rebuilding, you create your application directly in the cloud, taking advantage of all the tools available. The rebuild approach is often used when the new changes in the app require the code to be rewritten. In some cases, it may be more challenging to read the old code than to build it from zero.

Advantages: Building an application from the ground up will enable you to fully utilize everything the cloud has to offer. It is much easier to support and widen the app or service when it is built in the cloud from scratch.

Disadvantages: It takes time and effort to get a new application off the ground. Rebuilding the app or service in the cloud may potentially introduce new bugs that developers haven’t encountered in the legacy app.

The retire or retain approach

When you plan to migrate to the cloud, you may find that some applications are no longer necessary for your business and don’t need to be included in your migration plan. Alternatively, there may be applications that you use but don’t want to include in your migration for various reasons. The retire approach is used when the application or service is used infrequently or sporadically, and it’s not worth being rehosted, re-platformed, or re-architected to the cloud. In this case, the app can be retained on the local servers.

Advantages: The retiring approach helps you free up space on your on-premises servers, clear out your infrastructure, and eventually reduce costs. Additionally, retiring obsolete business applications can deliver significant cost savings, as substantial amounts of software budgets are spent on app maintenance.

Disadvantages: If an application’s maintenance and support costs are much higher than the usefulness it brings and you’ve decided to retire it, then it might require energy and effort to build a useful app from scratch.

After checking out the advantages and disadvantages of each approach, it is time you have a look at the collection of products and services that the top cloud providers recommend for the migration, in terms of the specific approaches your company would like to pursue.

Here you can find a comparison of the top cloud data migration service providers, including AWS, Azure, and Google Cloud.

What to choose: rehost, refactor, re-platform, re-architect, rebuild, or retain/retire?

The best cloud migration strategy depends on how much change your applications need and how much value you expect to gain from the cloud. Rehosting and replatforming can accelerate migration projects, while refactoring, re-architecting, and rebuilding are better suited for organizations looking to take fuller advantage of cloud capabilities.

Your cloud migration strategy will guide your entire migration process, which can last for months or even years. A common way to identify the most appropriate approach is through an Assessment and Discovery process. During this process, specialists create an inventory of your current systems and applications, evaluate migration risks and requirements, and determine the time and effort needed while keeping your business objectives in mind.

Benefits of cloud migration with Avenga

A well-planned cloud migration strategy is what separates a smooth transition from one that overruns budget and timeline. The choice of provider matters just as much as the choice of approach.

Avenga’s cloud migration services help you map your existing environment and plan the move, whether you’re migrating for the first time or scaling an existing deployment. Our cloud engineering track record spans multiple industries and technology stacks, which means the recommendation you get reflects your situation, not a preferred vendor’s roadmap.

Get in touch to talk through your options.

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Andrew Petryk

Engineering Director at Avenga