Rehost vs Rearchitect: Which Is The Right Financial Approach for Cloud Migration?

Jun 14 2016 | by Yoav Mor

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IT is the lifeblood of your enterprise. But, to maintain your business momentum and stay ahead of the competition, it’s essential you modernize, become more agile and break away from older technologies that hold you back.

The cloud offers you a cost-effective pathway to modernization. It provides modern streamlined development frameworks, better management of IT resource supply and demand, improved scalability and access to these resources from virtually anywhere in the world. And, with this improved agility, you can respond more quickly to market changes, drive innovation, exploit new business opportunities and fuel financial growth. But, in order to take advantage of what the cloud has to offer, you still need to spend time and money on establishing your cloud and migrating your applications and data to the new environment.

In this post, we take a brief look at the options available, before focusing on the financial drawbacks and benefits of the two main methods when migrating from on-premise to public IaaS—rehosting and rearchitecting.

The 5 Methods of Cloud Migration

According to Gartner, if you’re moving to the cloud, whether to Infrastructure, Platform or Software as a Service, you have a choice of 5 different methods of migration:

  • Rehost: Redeploying to an IaaS environment and changing the application’s configuration to work in a new virtual hardware environment.
  • Refactor: Redeploying to PaaS, thereby making use of familiar languages and frameworks while at the same time taking advantage of the cloud characteristics running on top of the provider’s infrastructure.
  • Revise: Modifying an existing codebase to meet cloud adoption or legacy modernization goals. Then rehosting or refactoring it to the cloud.
  • Rebuild: Discarding existing code and rearchitecting the application for a new software framework. Alternatively known as rearchitecting.
  • Replace: Discarding an existing application and using a proprietary pay-as-you-go SaaS solution instead.

Next, we’ll focus on rehost and rearchitect, which are the methods you’d consider when migrating from on-premise to public IaaS.

Financial Considerations of Rehosting

Also known as lift and shift, rehosting is often used as an intermediate step to cloud migration by breaking away from outdated physical hardware. This is also the case for refactoring and revising, where the financial and logistical considerations are very similar. The idea behind rehosting is to save time and money by replicating applications in the cloud, making only configuration changes without rewriting the application code. So it could be a quick fix to address the high running costs of an old on-premises infrastructure. Similarly, it will also appeal to enterprises planning a move to the cloud in order to avoid the capital investment of replacing or expanding existing infrastructure.

However, interdependencies between different systems could be a potential barrier to rehosting (owing to issues such as network security and bandwidth). But your business may benefit by rehosting specific stand-alone applications such as your company website. Also using public cloud to host temporary workloads, such as specific marketing campaigns, will eliminate the need to invest in additional hardware that might eventually end up unused.

Besides the capital cost savings and rapid procurement process, you should bear in mind the cost of training staff in the skills needed for a new IT environment. However, in the case of lift-and-shift, these will generally be the same as moving between on-premise VMs.

Financial Considerations of Rearchitecting

By nature, rearchitecting is far more time-consuming and expensive than rehosting. But rebuilding your applications from scratch will make your service infrastructure more streamlined, agile and better able to take advantage of cloud scalability and elasticity. For example, you can automate resource provisioning, which will reduce the time and cost of expanding your infrastructure to support business growth. Over time, this would make rearchitecting a better financial investment.

Resource-intensive applications, such as those used for large-scale data processing, will rack up the highest costs in the cloud and could also experience performance issues. So if you’re committed to a plan of cloud migration, it makes financial sense to rearchitect these applications—to make more efficient use of the cloud.

A decision to rearchitect will also be based on the long-term vision for an application. For example, you may want to repurpose a system that’s only used internally so it’s externally facing service too. Or whether you want to open up access through other devices, such as mobiles and tablets. And much will depend on whether an application will continue to maintain business value in the future.

In some respects, rearchitecting could be viewed as a lower risk strategy. This is because retrofitting a legacy application might not necessarily work or may end up being more work than you bargained for.

The Choice Is Yours

At first glance, rehosting may appear a more economical migration solution. But you may not get the same level of performance of a re-engineered solution or realize the full strategic benefits of the cloud. What’s more, cloud vendors may not be best suited to support your legacy applications. So, in some circumstances, rehosting may be more trouble than it’s worth.

On the other hand, once you’re in the cloud it’s easier to redevelop in the cloud. So, once you’ve migrated your applications, you can always rearchitect further down the line. Often a campaign of migration works best by adopting a hybrid approach—where you start out by rehosting and gradually rearchitect over time. But, whatever the case, don’t forget to draw up a Proof of Concept (POC) that you can present to decision makers, along with a migration plan outlining the first workloads you’ll move to the cloud.

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