Migrating to the cloud
Technique · Chapter 14
Why migrate a legacy app to the cloud
Section titled “Why migrate a legacy app to the cloud”Not every legacy app suits every cloud service, but a migration path usually exists. Benefits:
- Lower cost, plus greater availability and scalability.
- The provider owns hardware and infrastructure; depending on the model (IaaS, PaaS, FaaS) also the OS and other services.
- Reduced security exposure — the provider can handle OS updates and security patches for apps that were stuck on old hardware/software.
See Deploying to the cloud and Cloud-native applications.
The 6 R’s
Section titled “The 6 R’s”The migration path varies by organization and by application. The 6 R’s name six strategies:
| Strategy | What it means | When to use |
|---|---|---|
| Remove (retire) | Simply shut the app down | It’s no longer needed; a broad migration is a good moment to audit and cull unused apps. |
| Retain | Leave it in its current environment | No business case to move it (e.g. migration cost too high), or it’s kept on-premises as part of a hybrid cloud. |
| Replatform | Run it on cloud IaaS via emulators / a virtual machine | Can’t migrate natively but you don’t want to just retain it; lets you reach a newer platform/OS and its features. Tooling exists to assist. |
| Rehost | ”Lift and shift” — copy app and data from physical/virtual servers to IaaS unchanged | Quick, low-risk, easy; often the first step, later refactored to optimize for the cloud. |
| Repurchase | Buy a newer product (usually SaaS) and switch to it | Provider hosts everything; you only configure the software. |
| Refactor (re-architect) | Modify the app, possibly its architecture, for cloud-native features | Yields better availability, scalability, performance, and cost savings — but can be involved, slower, and costlier to execute. |
Related
Section titled “Related”Citations
Section titled “Citations”- Software Architect’s Handbook (Packt, 2018), Ch.14 “Migrating to the cloud”, pp. 1055-1062.