Migration strategy is a per-workload decision, not a company-wide one. A single organisation will typically rehost some systems, re-platform others, and rebuild a small number — and choosing one approach for everything is how migrations overrun.
Rehosting, or lift-and-shift, moves a workload with minimal change. It is fastest and lowest-risk, and it is the right answer for stable systems nearing end of life or workloads with a hard deadline like a data centre exit. It will not reduce your operating cost much, because you carry the same architecture and often the same inefficiency.
Re-platforming makes targeted changes without redesign: moving a self-managed database to a managed service, containerising an application, replacing a cron server with managed scheduling. This is usually the best cost-to-benefit ratio for systems that will run for years.
Re-architecting is justified when the current design blocks something the business needs — elastic scale, regional availability, or a release cadence the monolith cannot support. It is the most expensive path and should be reserved for workloads where the constraint is real and quantified.
Data migration deserves separate planning from application migration. Volume, acceptable downtime, and consistency requirements determine whether you can do a bulk transfer or need change-data-capture with a cutover window. This is where migrations most often slip.
Cost modelling before migration prevents unpleasant surprises. Cloud pricing rewards elastic, right-sized workloads and punishes over-provisioned always-on instances. A system that costs a fixed amount in a data centre can cost more in the cloud if you migrate its provisioning habits along with it.
Plan the landing zone first: network topology, identity and access boundaries, tagging standards, and logging. Retrofitting governance across dozens of migrated workloads is far harder than establishing it before the first one moves.
Finally, define rollback for every cutover. A migration you cannot reverse is a deployment you cannot safely attempt during business hours.