Legacy system migration is one of the most critical decisions facing IT leaders today. Organizations that choose the right migration strategy reduce project timelines by 40% and avoid costly rework that can derail digital transformation initiatives.
If you’re a CIO or IT Infrastructure Director evaluating legacy system modernization, understanding the “6 Rs” of cloud migration—and particularly the three most common strategies—is essential for making informed decisions. This guide breaks down rehost, replatform, and refactor approaches to help you choose the optimal path for each application in your portfolio.
Understanding the Migration Strategy Spectrum
The cloud migration strategies, commonly known as the “6 Rs,” provide a framework for application modernization decisions:
- Retire: Eliminate applications that are no longer needed
- Retain: Keep applications on-premises for now
- Rehost: “Lift and shift” to cloud infrastructure
- Replatform: “Lift, tinker, and shift” with minor optimizations
- Refactor: Architect for cloud-native capabilities
- Repurchase: Replace with SaaS solutions
While all six strategies have their place, rehost, replatform, and refactor represent the core approaches for most enterprise applications undergoing cloud migration.
Rehost: The “Lift and Shift” Approach
What is Rehosting?
Rehosting involves moving applications to the cloud with minimal or no changes to the application architecture, code, or functionality. Applications are migrated “as-is” to cloud infrastructure, typically using Infrastructure as a Service (IaaS) offerings.
Key characteristics of rehosting include:
- Minimal code changes: Applications run essentially unchanged in the cloud
- Fast migration timeline: Quickest path to cloud deployment
- Lower initial investment: Reduced development and testing requirements
- Immediate infrastructure benefits: Access to cloud scalability and reliability
When to Choose Rehost
Rehosting is optimal for:
- Applications with urgent compliance or data center exit requirements
- Legacy systems where source code or documentation is limited
- Applications with tight migration deadlines
- Workloads that need to prove cloud viability before further investment
- Systems with complex interdependencies that make changes risky
| Rehost Benefits | Rehost Limitations | Best Fit Applications |
|---|---|---|
| Fastest migration path | Limited cloud optimization | Monolithic enterprise applications |
| Lowest upfront costs | Potential for higher long-term costs | Time-sensitive migrations |
| Minimal business disruption | Missed modernization opportunities | Applications with unknown architecture |
Replatform: The “Lift, Tinker, and Shift” Strategy
What is Replatforming?
Replatforming involves making targeted optimizations to applications during migration without fundamental architectural changes. This approach captures some cloud benefits while maintaining core application functionality and business logic.
Common replatforming optimizations include:
- Database migration: Moving to managed database services
- Load balancer replacement: Using cloud-native load balancing
- Caching optimization: Implementing cloud-based caching solutions
- Monitoring integration: Adding cloud monitoring and logging
- Auto-scaling enablement: Configuring basic scaling policies
When to Choose Replatform
Replatforming works well for:
- Applications that can benefit from managed cloud services
- Systems where specific performance improvements are needed
- Workloads with clear optimization opportunities
- Applications where some modernization investment is justified
- Systems requiring compliance with cloud security standards
Organizations planning database migration initiatives often find replatforming provides the optimal balance of risk and reward for legacy applications.
Refactor: Cloud-Native Architecture Transformation
What is Refactoring?
Refactoring involves reimagining and rebuilding applications to fully leverage cloud-native capabilities. This approach typically includes architectural changes, code modernization, and adoption of cloud services and patterns.
Refactoring initiatives commonly involve:
- Microservices architecture: Breaking monoliths into distributed services
- Containerization: Packaging applications for container orchestration
- API-first design: Creating modern integration interfaces
- Event-driven patterns: Implementing asynchronous communication
- Cloud-native services: Leveraging PaaS and serverless technologies
When to Choose Refactor
Refactoring is justified for:
- Applications critical to competitive advantage
- Systems requiring significant scalability improvements
- Applications with performance or reliability issues
- Workloads that need rapid feature development
- Systems where technical debt significantly impacts business agility
Decision Framework: Choosing Your Migration Strategy
Application Assessment Criteria
Evaluate each application across multiple dimensions to determine the optimal migration strategy:
- Business criticality: Impact on revenue, customer experience, and operations
- Technical complexity: Architecture, dependencies, and integration points
- Performance requirements: Scalability, availability, and response time needs
- Compliance constraints: Regulatory, security, and data residency requirements
- Development resources: Available skills, timeline, and budget
Risk vs. Reward Analysis
Each migration strategy involves different risk and reward profiles:
- Rehost: Low risk, moderate reward – Quick cloud benefits with minimal disruption
- Replatform: Medium risk, good reward – Balanced approach with targeted improvements
- Refactor: High risk, high reward – Maximum cloud benefits with significant investment
Consider implementing a phased approach where applications are initially rehosted or replatformed, then refactored over time as business value and technical understanding justify the investment.
Portfolio-Level Migration Planning
Wave-Based Migration Approach
Organize your migration into waves based on complexity, dependencies, and business value:
- Wave 1 – Quick Wins: Simple applications suitable for rehosting
- Wave 2 – Optimization: Applications benefiting from replatforming
- Wave 3 – Transformation: Core systems requiring refactoring
- Wave 4 – Innovation: New capabilities and advanced cloud services
Dependency Mapping
Understanding application dependencies is crucial for migration sequencing:
- Data dependencies: Shared databases and data flows
- Service dependencies: API calls and integration points
- Infrastructure dependencies: Shared middleware and platform services
- Business process dependencies: Workflow and operational connections
For complex enterprise environments, application dependency mapping becomes essential for successful migration planning and execution.
Implementation Best Practices
Rehost Implementation
Successful rehosting requires attention to:
- Server sizing: Right-sizing cloud instances for workload requirements
- Network configuration: Maintaining connectivity and security
- Data migration: Ensuring data integrity during transfer
- Performance validation: Confirming application performance post-migration
Replatform Implementation
Effective replatforming focuses on:
- Service selection: Choosing appropriate managed services
- Configuration optimization: Tuning for cloud environment
- Integration testing: Validating modified components
- Performance monitoring: Measuring improvement gains
Refactor Implementation
Successful refactoring requires:
- Architecture planning: Designing cloud-native architecture
- Incremental delivery: Breaking work into manageable phases
- Testing strategy: Comprehensive functional and performance testing
- Change management: Preparing teams for new operational models
Cost Considerations Across Strategies
Total Cost of Ownership (TCO)
Evaluate the full cost impact of each migration strategy:
- Migration costs: Development, testing, and deployment expenses
- Operational costs: Ongoing cloud infrastructure and management
- Opportunity costs: Delayed benefits from more advanced cloud capabilities
- Technical debt costs: Future modernization requirements
ROI Timeline
Different strategies deliver returns on different timelines:
- Rehost: Immediate infrastructure cost benefits, longer-term optimization gains
- Replatform: Medium-term performance and cost improvements
- Refactor: Long-term business agility and competitive advantages
Success Metrics and Monitoring
Establish clear success criteria for each migration strategy:
- Migration metrics: Timeline adherence, budget compliance, defect rates
- Performance metrics: Response times, availability, throughput
- Cost metrics: Infrastructure costs, operational efficiency
- Business metrics: User satisfaction, feature delivery velocity
Remember that migration is often a journey rather than a destination. Many organizations start with rehost or replatform approaches and evolve applications toward cloud-native architectures as business value and technical requirements justify the investment.
Ready to plan your legacy migration strategy? Start by conducting a comprehensive application portfolio assessment to identify the optimal migration approach for each system in your environment.
