• Application in general meets the immediate needs of the business, and
there is no need to change any functionality
You can easily argue that such criteria may also call for refactor and/or replace,
to break the application into components for easier management, scaling,
automation, new features, etc. These are valid options, but a rehost is usually
considered preferable in the context of cost, effort and duration. Depending on
the application’s specific functionality, it will typically take longer to refactor
an application due to additional coding and testing, as opposed to rehost or
replatform options.
In our experience, even with rehost migration patterns, it is common to take
on minor replatforms of certain components, optimizing the application to
gain the benefits of the target platform and the migration effort. The most
common components that are candidates for replatform are OS, database,
batch jobs and load balancers.
An example of a rehost with minor replatform migration is a commercial off-
the-shelf (COTS) business intelligence application that was moved to Azure.
The application was based on Microsoft Windows Server, IIS/ASP.NET and
Microsoft SQL Server. Even though the application was moved “as is” using
Azure Recovery Service, we were able to replatform the database layer. The
database component was moved to a managed SQL platform to reduce the
database administration overhead. In addition, the application gained some
benefits by leveraging Azure Traffic Manager and Virtual Machine Scale Sets
for load balancing, high availability and auto recovery functionality. In a data
center exit scenario with time constraints, this approach is the most viable
option.
Replatform
In a Replatform migration scenario, the application is moved “as is,” but certain
application components will be moved to a different platform. Many compo-
nents are candidates for replatform, including OS, web and app layers, data-
base, message queuing, batch processing, Java application layer, etc.
The following are the general criteria describing an application suitable for a
replatform migration pattern:
• Custom, traditional three-tier application
• Individual services or components
• Address current challenges on scaling and elasticity due to platform or
licensing costs
• Desire to reduce administrative overhead
26 | THE DOPPLER | FALL 2018