The Six Rs of Cloud Migration
AWS popularized the “6 Rs” framework that categorizes migration strategies from simplest to most transformative. Understanding these strategies is essential for making workload-level decisions:
- Rehost (Lift and Shift), Move applications as-is to cloud VMs (EC2/Azure VMs). Fastest approach with minimal code changes. Ideal for: legacy applications, time-sensitive migrations, applications pending retirement.
- Replatform (Lift, Tinker, and Shift), Make targeted optimizations during migration without changing core architecture. Examples: moving from self-managed MySQL to Amazon RDS or Azure Database, shifting from on-prem load balancers to ALB/Azure Load Balancer.
- Repurchase (Drop and Shop), Replace existing applications with SaaS equivalents. Examples: on-prem email to Microsoft 365, on-prem CRM to Salesforce, on-prem HR systems to Workday.
- Refactor (Re-architect), Redesign applications to be cloud-native using microservices, containers, and serverless. Highest effort but greatest long-term benefit. Ideal for: strategic applications, high-scale workloads, applications needing rapid feature iteration.
- Retain, Keep certain workloads on-premise due to compliance, latency, or cost considerations. Common for: mainframe systems, applications with strict data sovereignty requirements.
- Retire, Identify and decommission applications that are no longer needed. Typical migrations find 10-20% of the application portfolio can be retired.
Pre-Migration Assessment
Before moving a single workload, a thorough assessment phase is critical. This phase typically spans 4-8 weeks and produces the migration plan that guides all subsequent work.
Application Discovery and Dependency Mapping
The foundation of any migration plan is understanding what you have and how it connects. Tools like AWS Application Discovery Service, Azure Migrate, or open-source alternatives like NetBox and RackTables help map:
- Server inventory (CPU, memory, storage, OS, installed software)
- Network dependencies (which servers communicate, on which ports, how frequently)
- Data dependencies (shared databases, file shares, message queues)
- External integrations (APIs, partner connections, Internet-facing services)
TCO Analysis and Cost Modeling
Cloud cost optimization begins before migration. Use the AWS Pricing Calculator and Azure Pricing Calculator to model costs under different scenarios. Key considerations:
- Right-sizing, On-premise servers are typically provisioned for peak load. Cloud instances should be sized for actual utilization with auto-scaling handling peaks.
- Reserved capacity, AWS Reserved Instances and Azure Reserved VM Instances offer 30-72% savings for predictable workloads.
- Storage tiering, Not all data needs high-performance storage. S3 Intelligent Tiering and Azure Blob storage tiers automatically optimize costs.
- Data transfer costs, Egress charges are often the most surprising cloud cost. Plan for inter-region, cross-AZ, and Internet-bound transfer volumes.
AWS vs Azure: Platform Considerations
Both AWS and Azure are mature, enterprise-grade platforms. The choice often depends on existing technology investments and team expertise rather than technical capability:
AWS strengths: Broadest service catalog (200+ services), most mature platform (launched 2006), largest market share and community, strongest in containers (EKS/ECS) and serverless (Lambda). Best for: greenfield cloud-native development, organizations without strong Microsoft investments.
Azure strengths: Deepest Microsoft integration (Active Directory, Office 365, SQL Server), hybrid cloud leadership (Azure Arc, Azure Stack), strong enterprise compliance certifications, competitive VM pricing. Best for: Microsoft-centric enterprises, hybrid cloud strategies, organizations with Enterprise Agreements.
Multi-cloud reality: Many enterprises adopt both platforms, running different workloads on the platform that best suits each. Kubernetes and Terraform enable workload portability across clouds, reducing vendor lock-in risk.
Migration Execution: Wave Planning
Enterprise migrations execute in waves, groups of related applications migrated together over a planned timeline. Wave planning considers:
- Wave 0 (Foundation), Establish cloud landing zone: networking (VPC/VNet), identity (IAM/Azure AD), security baselines, monitoring, and CI/CD pipelines.
- Wave 1 (Pilot), Migrate 2-3 low-risk, independent applications to validate the process, build team confidence, and refine runbooks.
- Wave 2-N (Production), Progressively migrate application groups, ordered by dependency and business criticality. Database migrations typically represent the highest-risk items and require careful planning for data sync and cutover.
- Wave Final (Optimization), Post-migration optimization: right-size instances, implement auto-scaling, enable cost alerts, and decommission on-premise infrastructure.
Security and Compliance in the Cloud
Cloud migration does not eliminate security responsibilities, it redistributes them under the shared responsibility model. The cloud provider secures the infrastructure; you secure your data, identities, and configurations. Critical post-migration security measures include:
- Enable cloud-native security services (AWS GuardDuty, Azure Defender)
- Implement least-privilege IAM policies from day one
- Encrypt data at rest and in transit (KMS/Azure Key Vault)
- Enable audit logging (CloudTrail/Azure Activity Log) with centralized SIEM integration
- Conduct regular configuration audits using AWS Config or Azure Policy
Conclusion
Cloud migration is a strategic transformation, not a simple infrastructure move. Success requires careful assessment, workload-appropriate strategy selection, wave-based execution, and continuous optimization. Organizations that treat migration as a one-time project rather than an ongoing journey often find themselves with inflated cloud bills and underperforming architectures. The cloud rewards those who plan deliberately and optimize continuously.