Approaches
Rehost
Moving a system to new infrastructure without changing the application. It is usually the lowest-risk modernisation step, and it often buys time to plan the larger changes properly.
Part of Maintenance & Modernization
Rehosting, often called lift-and-shift, moves a workload to new infrastructure, such as another data centre or cloud virtual machines, without changing the application itself.
What it solves
Rehosting deals with infrastructure risk: hardware reaching end of life, a data centre contract ending, or an operating system losing support. It is usually quicker than the other options, and while the old environment still runs, traffic can be switched back if something goes wrong. It also buys time, because decisions about the application can be made once the infrastructure deadline has passed.
What it leaves unchanged
Everything inside the application stays as it was. If changes were slow before, they remain slow, and a design that could not scale still cannot. Running costs on cloud infrastructure can end up higher than before, because much of the cloud's cost advantage comes from scaling on demand and from managed services, and a straight rehost uses neither. We include running-cost estimates in the migration plan for this reason.
When it is the right call
We recommend rehosting when the main driver is an infrastructure deadline and the application is stable and still does its job. It also works as the first phase of a longer programme, with replatforming or refactoring planned for later.