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At a glance
- Rehosting an oversized server keeps it oversized; right-size first.
- Replatforming needs compatibility checks, such as SQL features on managed databases.
- Retaining or retiring an application can be the right answer.
Three migration approaches compared
Swipe or scroll sideways to compare all options.
| Decision point | Rehost | Replatform | Refactor / re-architect |
|---|---|---|---|
| Price basis | Migration labor plus the resulting cloud infrastructure | Migration and adaptation labor plus selected managed services | Development project plus new services and ongoing engineering |
| Universal project price | None; requires an application-specific estimate | None; requires an application-specific estimate | None; requires an application-specific estimate |
| Application change | Limited change to application architecture | Targeted platform changes while retaining much of the application | Significant architecture or component redesign |
| AWS example | Move an existing server workload to EC2 | Move a suitable database to Amazon RDS | Redesign selected functions around cloud-native services |
| Initial engineering | Usually the least architecture change of these options | Additional compatibility and platform work | The most substantial redesign and testing scope |
| Operational responsibility | Much of the server/application administration remains | Some infrastructure tasks shift to managed services | Responsibility changes with the redesigned services |
| Main cost risk | Paying for an inefficient server configuration in a new location | Underestimating compatibility changes and managed-service charges | Underestimating development, testing, and parallel operation |
| Main limitation / extra cost | Existing inefficiency can move into the new cloud bill | Compatibility work and managed-service charges may offset operational savings | Development, parallel operation and migration risk can dominate initial cost |
| Best fit (Sigma assessment) | A near-term relocation matters more than redesigning the application | A specific managed-service benefit is achievable without a full rewrite | The business needs architectural changes that justify development and testing |
| Official sources | Amazon Web Services: Migration strategies: rehost, replatform, refactor | Amazon Web Services: Migration strategies: rehost, replatform, refactor | Amazon Web Services: Migration strategies: rehost, replatform, refactor |
Moving a server does not guarantee savings
Rehosting can meet a data-center exit deadline, but an oversized machine remains oversized after the move. Calculate the target compute, storage, backup, networking, licensing, and management costs. Then identify whether resources can be reduced or scheduled without disrupting the application.
Replatforming can reduce some administrative work, but a managed database has its own price and compatibility requirements. For example, moving SQL Server to a managed service requires checking the application's supported database features and operational dependencies. Do not assume every server-level function transfers unchanged.
Refactor only when the outcome justifies the project
Refactoring may be appropriate when the business needs capabilities that the existing design cannot reasonably provide. Define that result in measurable terms: supported transaction volume, recovery behavior, release process, or an application feature. A fashionable architecture is not a financial justification.
Include testing, data migration, parallel running, staff skills, and support after launch. The lowest estimated infrastructure bill can be outweighed by an unnecessary development project.
AWS describes additional choices, including retaining or retiring workloads. A useful assessment can conclude that an application should stay where it is or be replaced by a service rather than moved through one of these three paths.
Sigma can help compare a scoped migration proposal using the same application, performance requirement, and operating period. The decision should connect the amount of change to a business result and a complete cost.
Questions to ask before you buy
- What business result must the migration deliver?
- Is the application supported on the target platform or managed service?
- What are the one-time project cost and the ongoing monthly cost?
- Should any applications be retired or replaced instead?
Frequently asked questions
Which cloud migration strategy is cheapest?
Rehosting usually has the lowest project cost, but it may not lower running costs. Compare project and operating costs over the same period.
Sources and pricing notes
Prices and specifications checked September 27, 2026 against the providers’ published sources below. Prices are US list or published rates before taxes, fees and equipment unless stated; offers change, so confirm the current terms before you buy.
- Amazon Web Services. Migration strategies: rehost, replatform, refactor
- Amazon Web Services. Migration strategy recommendations
- Amazon Web Services. A rehost migration playbook: Cost components
How Sigma is paid. Sigma is a Hawaiʻi technology advisor. Provider or reseller partners compensate Sigma; product and service prices may include a margin. No procurement fee applies. Standalone consulting is quoted separately.