Lift and Shift

Lift and shift, also called rehosting, moves an application to a different hosting environment without redesigning the application. AWS uses rehost for moving an application unchanged; GOV.UK includes rehosting among its legacy-management options. Preserving application structure can reduce the work required during a move, but destination compatibility, configuration, connectivity, and operations still need validation. Compare approved behavior and data at agreed points, including intended differences, and separately test security, performance, and recovery. For large migrations AWS generally favors rehosting, relocating, or replatforming before further modernization, with exceptions when those approaches are not acceptable.

What moves and what does not

The hosting environment changes, and infrastructure responsibilities, security controls, support arrangements, and costs may change with it. Application design problems, unsupported application components, or difficult change procedures can remain if the work does not address them. Reassess each legacy system against its actual unmet needs instead of assuming that every risk either disappears or stays constant. In a fictional utility, all forty-one unsupported applications remained unsupported after three hundred servers were rehosted. Its bill also rose, but a larger cloud bill alone would not measure technical-debt interest. That interest is additional effort or cost attributable to a particular technical problem; the total bill also pays for useful service. Compare costs over the same period, workload, service level, and accounting scope before attributing a difference to rehosting or debt.

Rehosting can fit a deadline when the destination is compatible and the remaining risk is acceptable. It may be the whole task for an application that meets its needs, or a stage before approved modernization. In the latter case, preserve the later work’s owner, resources, timing, and review conditions. Where the application itself prevents the required outcome, moving it alone is insufficient; that does not prohibit rehosting as an intermediate step. The relationship between the work and its promises is explored in Three Hundred Servers Moved and Nothing Changed. The definitions, strategy choices, and distinction between change scope and rollout sequence are explained in modernization and migration.

References:

• AWS Prescriptive Guidance, About the migration strategies, Large migration guide.
• Government Digital Service and Central Digital and Data Office, Managing legacy technology, 2019 (Open Government Licence v3.0).