📦 Rehost Strategy Overview

Lift and Shift: Moving to Azure with minimal changes

🎯 What is Rehost (Lift & Shift)?

Rehosting is the process of moving applications from on-premises infrastructure to Azure cloud without modifying the application code. Think of it as relocating your office to a new building - you’re moving the same furniture and equipment, just to a better location.

🏗️ Core Concept 

---
title: Rehost Migration Process
---
flowchart LR
    subgraph OnPrem [🏢 On-Premises]
        A[💻 Physical Servers]
        B[🗄️ Local Storage]
        C[🌐 On-Prem Network]
        D[📱 Applications]
    end
    
    subgraph Azure [☁️ Azure Cloud]
        E[🖥️ Azure VMs]
        F[💾 Azure Disks]
        G[🌐 Virtual Network]
        H[📱 Same Applications]
    end
    
    A -.->|Lift & Shift| E
    B -.->|Migrate| F
    C -.->|Recreate| G
    D -.->|Unchanged| H
    
    style OnPrem fill:#ffebee,stroke:#c62828
    style Azure fill:#e3f2fd,stroke:#1976d2

✅ Key Benefits of Rehost

🚀 Speed & Simplicity

  • ⚡ Fastest migration path - typically weeks vs. months
  • 🔧 Minimal complexity - no code changes required
  • 📋 Predictable process - well-established methodologies
  • 👥 Lower skill requirements - infrastructure focus vs. development

💰 Cost Effectiveness

  • 🎯 Lower upfront investment in migration effort
  • 💵 Immediate cost benefits from cloud infrastructure
  • 📊 Predictable migration costs - mainly infrastructure setup
  • ⏰ Faster time to value - quicker business benefits

🛡️ Risk Reduction

  • 🔒 Application stability - no code changes mean lower risk
  • 📋 Proven migration patterns - mature tooling and processes
  • 🔙 Easier rollback if issues occur
  • 👨‍💼 Business continuity - minimal disruption to operations

📈 Strategic Advantages

  • 🏁 Quick wins for cloud adoption initiatives
  • 🎓 Learning opportunity for cloud operations
  • 🔄 Foundation for future optimization - can refactor later
  • ✅ Compliance maintenance - keeps existing security posture

🎯 Ideal Rehost Scenarios

✅ Perfect Candidates

🏢 Legacy Enterprise Applications 

Examples:
├── 📊 ERP Systems (SAP, Oracle)
├── 🗄️ Legacy databases with complex schemas
├── 📝 Document management systems
└── 🔧 Custom business applications with dependencies

⏰ Time-Critical Migrations 

Scenarios:
├── 🏢 Data center closures or lease expiration
├── 📋 Compliance mandates with tight deadlines
├── 💰 Budget cycles requiring quick cloud adoption
└── 🛡️ Security incidents requiring rapid migration

🛠️ Complex Dependencies 

Characteristics:
├── 🔗 Tightly coupled application components
├── 🗄️ Shared databases across multiple applications
├── 🌐 Complex networking requirements
└── 🔐 Specialized security configurations

🚫 Rehost Limitations

⚠️ What Rehost Doesn’t Provide

  • 📈 Limited performance optimization - same application bottlenecks remain
  • 💰 Higher long-term costs - VM management overhead continues
  • 🔧 Ongoing maintenance burden - OS patching, security updates
  • 📊 No cloud-native benefits - auto-scaling, managed services

🛑 Poor Rehost Candidates

❌ Applications That Shouldn’t Be Rehosted 

Avoid Rehost for:
├── 🕰️ End-of-life applications (retire instead)
├── 📱 Modern web applications (refactor to PaaS)
├── 🔄 Applications with frequent updates (benefit from DevOps)
└── 💸 Cost-sensitive workloads (PaaS often cheaper)

🏗️ Azure Rehost Architecture

🖥️ Core Azure Services for Rehost 

---
title: Typical Rehost Architecture
---
flowchart TB
    subgraph Management [🛠️ Management Layer]
        A[🔍 Azure Monitor]
        B[🛡️ Azure Security Center]
        C[🔄 Azure Backup]
    end
    
    subgraph Compute [💻 Compute Layer]
        D[🖥️ Azure VMs]
        E[📊 VM Scale Sets]
        F[⚖️ Load Balancer]
    end
    
    subgraph Storage [💾 Storage Layer]
        G[💿 Premium SSD]
        H[🗄️ Standard Storage]
        I[📁 File Shares]
    end
    
    subgraph Network [🌐 Network Layer]
        J[🏠 Virtual Network]
        K[🚪 Network Security Groups]
        L[🔗 VPN Gateway]
    end
    
    Management --> Compute
    Compute --> Storage
    Compute --> Network
    
    style Management fill:#fff3e0,stroke:#f57c00
    style Compute fill:#e8f5e8,stroke:#388e3c
    style Storage fill:#f3e5f5,stroke:#7b1fa2
    style Network fill:#e3f2fd,stroke:#1976d2

🛠️ Service Mapping Guide

On-Premises Component Azure Equivalent Purpose
🖥️ Physical Servers Azure Virtual Machines Primary compute resources
💾 Local Storage Azure Managed Disks Persistent storage for VMs
🌐 Network Switches Virtual Network Network connectivity
🔥 Firewalls Network Security Groups Traffic filtering
⚖️ Load Balancers Azure Load Balancer Traffic distribution
📊 Monitoring Tools Azure Monitor Performance monitoring
🔄 Backup Systems Azure Backup Data protection

📊 Rehost vs. Stay On-Premises

💰 Cost Comparison Example 

---
title: 3-Year Cost Comparison
---
xychart-beta
    title "Total Cost of Ownership (3 Years)"
    x-axis [Year 1, Year 2, Year 3]
    y-axis "Cost ($1000s)" 0 --> 200
    bar [150, 120, 120]
    line [100, 85, 85]

📈 Breakdown:

  • 🔴 On-Premises Bar: Hardware refresh, maintenance, facility costs
  • 🔵 Azure Rehost Line: VM costs with reserved instances and optimization

⚡ Performance Considerations

Aspect On-Premises Azure Rehost Notes
🚀 Performance Baseline Similar to baseline Network latency may vary
📈 Scalability Limited by hardware Manual scaling Can add VMs as needed
🔄 Availability Hardware dependent 99.95% SLA Azure infrastructure reliability
🛡️ Security Your responsibility Shared responsibility Azure handles infrastructure security

🎯 Success Metrics

📊 Key Performance Indicators (KPIs)

✅ Migration Success Metrics

  • ⏰ Migration timeline adherence (target: within planned schedule)
  • 💰 Budget compliance (target: within 10% of estimated costs)
  • 🔧 Application functionality (target: 100% feature parity)
  • 📊 Performance baselines (target: maintain or improve response times)

📈 Post-Migration Benefits

  • 💵 Infrastructure cost reduction (typical: 20-30% Year 1)
  • ⚡ Improved availability (target: >99.9% uptime)
  • 🛡️ Enhanced security posture (Azure security features)
  • 🔄 Backup and recovery improvement (target: RTO/RPO improvements)

📋 Success Criteria Checklist

  • 🎯 All applications migrated without functionality loss
  • 👥 User acceptance achieved with minimal complaints
  • 📊 Performance benchmarks met or exceeded
  • 🛡️ Security compliance maintained or improved
  • 💰 Cost targets achieved within tolerance
  • 📚 Knowledge transfer completed to operations team

🔄 Post-Rehost Optimization

🎯 Quick Wins After Migration

💰 Cost Optimization 

Immediate Actions:
├── 🏷️ Apply Azure Reserved Instances (save 30-70%)
├── 📊 Right-size VMs based on actual usage
├── ⏰ Schedule non-production VMs (auto-shutdown)
└── 🗄️ Optimize storage tiers (hot/cool/archive)

⚡ Performance Optimization 

Quick Improvements:
├── 🚀 Premium SSD for database VMs
├── 📊 Enable accelerated networking
├── 🔄 Implement Azure Load Balancer
└── 📈 Set up auto-scaling for predictable workloads

🚀 Future Modernization Path 

---
title: Rehost to Modern Architecture Journey
---
flowchart LR
    A[📦 Rehost<br/>IaaS VMs] --> B[🔧 Optimize<br/>Right-size, Monitor]
    B --> C[🔄 Containerize<br/>Docker + AKS]
    C --> D[☁️ Cloud-Native<br/>PaaS Services]
    
    A1[⏰ 0-3 months] --> A
    B1[⏰ 3-6 months] --> B
    C1[⏰ 6-12 months] --> C
    D1[⏰ 12+ months] --> D
    
    style A fill:#f3e5f5,stroke:#4a148c
    style B fill:#fff3e0,stroke:#f57c00
    style C fill:#e3f2fd,stroke:#1976d2
    style D fill:#e8f5e8,stroke:#388e3c

🎯 Key Takeaways

  • 📦 Rehost is the fastest path to cloud adoption with minimal risk
  • 💰 Provides immediate infrastructure benefits without code changes
  • 🎯 Ideal for legacy applications and time-critical migrations
  • 🔧 Limited optimization benefits compared to cloud-native approaches
  • 🚀 Serves as foundation for future cloud modernization
  • 📊 Success depends on proper planning and realistic expectations

📖 Next Steps: