How to Migrate to the Cloud Without Downtime: A Practical AWS, Azure and GCP Checklist

Moving applications to the cloud promises scalability, resilience and faster delivery, but a poorly planned migration can cause outages, data loss and unexpected bills. The good news is that most risks are predictable. This checklist walks through the phases of a low-downtime migration.

Phase 1: assess what you have

• Inventory everything: applications, databases, file stores, scheduled jobs, integrations, DNS records, certificates and licenses.
• Map dependencies: which systems talk to which, and which external partners connect to you.
• Measure baselines: CPU, memory, storage, traffic patterns and response times, so you can size resources and compare after migration.
• Classify data: identify personal, financial or health data and any residency requirements.

Phase 2: choose a strategy per application

The industry often describes migration options as the “Rs”:

• Rehost (lift and shift): move virtual machines as they are. Fastest, least optimization.
• Replatform: small changes, such as moving to a managed database or containers.
• Refactor: redesign for cloud-native services. Most benefit, most effort.
• Repurchase: replace with a SaaS product.
• Retire or retain: switch off what is unused; keep what must stay on-premises for now.

Most organizations use a mix: rehost first to exit a data center quickly, then optimize the most important systems.

Phase 3: build the landing zone

• Account or subscription structure, networking and VPN or private connectivity.
• Identity and access management with least privilege and multi-factor authentication.
• Infrastructure as code (Terraform, CloudFormation or Bicep) for repeatable environments.
• Logging, monitoring, alerting and budget alerts from day one.
• Backup and disaster recovery policies.

Phase 4: migrate data safely

• Use continuous replication for databases so the cloud copy stays in sync until cutover.
• Validate data with row counts, checksums and application-level checks.
• Rehearse the migration in a staging environment and time each step.

Phase 5: plan the cutover

1. Lower DNS time-to-live values a few days before the switch.
2. Freeze non-essential changes during the migration window.
3. Stop writes briefly, let replication catch up, then point traffic to the cloud.
4. Run smoke tests on critical user journeys immediately.
5. Keep the old environment available for a defined rollback window.

For zero-downtime requirements, blue-green deployments or gradual traffic shifting through a load balancer let you move a small percentage of users first and roll back instantly if needed.

Phase 6: optimize after migration

• Right-size instances using real usage data.
• Adopt managed services where they reduce operational load.
• Set up autoscaling and scheduled shutdown of non-production environments.
• Review costs weekly for the first few months.

Common pitfalls

• Forgetting hidden dependencies such as cron jobs, hard-coded IP addresses or email relays.
• Underestimating data transfer time for large databases.
• Copying on-premises security assumptions instead of using cloud-native controls.
• No rollback plan.

Learn more about our cloud migration and DevOps services.

Frequently asked questions

How long does a cloud migration take?

A small application can move in a few weeks. Larger portfolios are usually migrated in waves over several months, starting with lower-risk systems.

Is lift and shift a bad idea?

Not necessarily. It is a fast way to exit a data center. The key is to follow it with right-sizing and selective modernization so you capture cloud benefits.

Which cloud provider should we choose?

AWS, Azure and Google Cloud are all strong. Existing skills, Microsoft licensing, data and AI services, and regional availability usually decide the choice.