Cloud & Infrastructure · 7 min
Cloud migration without downtime: strategy and checklist
A cloud migration without downtime is possible when the migration is designed in phases, with replicated data and a rollback plan, instead of being carried out in a single «big bang» step. The goal is not just to move systems, but to do so while maintaining service continuity and keeping costs and risks under control.
Key points
- Phased migration and rollback, not a single «big bang» step.
- Choose the strategy (rehost/replatform/refactor) app by app.
- Parallel data replication to shift traffic gradually.
- After the migration: cost governance and security review.
Migration strategies (the «R»s)
There is no single way to migrate. The most common strategies differ in how much the application is modified: from a simple move to a rewrite. Choosing the right mix, application by application, is the decision that determines cost, time and risk.
- Rehost («lift and shift»): move without changes, fast but poorly optimised.
- Replatform: small adjustments to make better use of the cloud.
- Refactor: rewrite parts of the app for better scalability and costs.
- Retire / Retain: decommission or keep on-premise what is not worth migrating.
How to avoid downtime
Downtime is avoided by designing the transition, not the switch. The key techniques are: phased migration (one service at a time), parallel data replication before the cutover, test environments that replicate production, and a switch window with a rollback plan if something does not work.
For data, continuous synchronisation between the old and new environment makes it possible to «shift traffic» gradually and to roll back without losses in case of problems.
Costs, security and continuous optimisation
The cloud does not reduce costs automatically: without governance it can increase them. After the migration you need spend monitoring (FinOps), correct resource sizing and periodic review. On the security side, the migration is the opportunity to redesign access, encryption and backups according to best practices.
FAQ
Is it really possible to migrate without service interruptions? +
Yes, with phased migration, parallel data replication and a rollback plan. Downtime almost always comes from «big bang» migrations without preparation.
Does the cloud automatically save money? +
No. The cloud can reduce costs only with governance and continuous optimisation. Without spend control, it can end up more expensive than on-premise.
How long does a cloud migration take? +
It depends on the number and complexity of the systems. A phased approach lets you gain benefits from the first migrated services, without waiting for the end of the entire programme.
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