Encapsulation is the simplest approach, and you may want to take this if the system is business-critical and needs to communicate with other applications running on the latest technology. In the encapsulation approach, you need to build an API wrapper around your legacy system, which will allow other business applications to communicate with a legacy application. An API wrapper is a common approach whereby you start migrating your applications to the cloud but need to keep the legacy application in the on-premises data center for modernization in the later phase. You can choose the encapsulation option if your legacy code is well written and maintained, but, again, you will not be able to get the benefit of technology advancement and hardware flexibility.

The rehosting approach is also among the most straightforward approaches, whereby you want to migrate your application into another hardware provider such as the Cloud without any changes in code. Again, as with encapsulation, the rehosting option can save some cost due to vendor contracts but may not give you benefits from technology advancement and hardware flexibility. An organization often takes this approach when it needs to move out of an existing contract quickly. For example, you can take the first step to the cloud in phase one and go for application modernization in phase two.

The re-platforming approach may get a bit more complex than the rehosting approach and provides the immediate benefit of a new operating system. Organizations often choose this approach if the server is going End of Life (EOL), where no support is available and an upgrade becomes necessary to handle security issues. For example, if Windows Server 2008 is going EOL, you may want to upgrade the operating system to the Windows 2012 or 2016 version. You need to rebuild your binaries with the new operating system and perform testing to make sure everything works properly, but there are no significant changes in the code as such. Again, as with rehosting, re-platforming may not give you benefits from technology advancement. However, it will allow you to have continuous support from the vendor.

While the preceding three approaches are the simplest ones, they are not able to provide the full benefit of the application upgrade. Let's look at approaches that help you to take full advantage of application modernization.