1. Lift & Shift
With this migration strategy you move workloads from a source environment to a target environment with minor to no modifications or refactoring.
The modification you apply to the workloads in order to migrate are only the minimal changes needed in order for the workloads to operate in the target environment.
This strategy is ideal when a workload can operate as is in the target environment or when there is little to no business need for change. It also can extend the life of an application by addressing resources and scaling limitation previously faced on the on-prem site.
Pro: Lift and shift are be low risk and offer quick access to the cloud.
2. Improve & Move
You modernize and improve the workload while migrating it to the cloud.
Before moving the workload or the application to the new environment an exercise in improving or recoding the solution is undertaken. Without this changes the service might not function adequately in the new location.
Pro: as Lift & Shift plus equal or better service performances.
3. Rebuild
In this approach you decommission the existing application and completely redesign / rewrite it as a cloud native application.
If the current app isn’t meeting your goals or it’s too costly, for example, you don’t want to maintain it.
4. Do Nothing
Sometimes keeping a specific workload on-premises is the only option. It’s usually because of technical limitations.
For instance, dependencies on mainframe machines, incompatible licensing with the cloud environment, compliance constraints like data locality in a specific country that doesn’t have a cloud data center, unsupported operating system like Windows desktop images, servers and virtual appliances.
Source: Coursera.