###############################
11.0.7 Cloud Migration Strategy
###############################

Moving to the cloud is a journey, not a destination. Let's explore smart migration strategies that build on your container expertise.

===========================
The 6 Rs of Cloud Migration
===========================

.. note::

   Moving to the cloud is a process that involves planning, preparation, and execution. It can be a complex and challenging undertaking, but it offers many benefits, including scalability, flexibility, cost savings, and ease of use.

**Migration Approaches Overview:**

.. code-block:: text

   The 6 Rs Migration Strategy:
   
   Rehost     (Lift and Shift)
   Replatform (Lift, Tinker, and Shift)  
   Refactor   (Re-architect)
   Retire     (Turn off)
   Retain     (Keep as is)
   Repurchase (Buy new)

==========================
1. Rehost (Lift and Shift)
==========================

**What it means:** Move applications to cloud with minimal changes

.. code-block:: text

   Traditional Approach:
   ┌─────────────────────────────────────┐
   │ Physical Server                     │
   │ ├─ Windows Server 2019              │
   │ ├─ IIS Web Server                   │
   │ ├─ .NET Application                 │
   │ └─ SQL Server Database              │
   └─────────────────────────────────────┘
           │ (Rehost)
           ▼
   ┌─────────────────────────────────────┐
   │ Cloud Virtual Machine               │
   │ ├─ Windows Server 2019              │
   │ ├─ IIS Web Server                   │
   │ ├─ .NET Application                 │
   │ └─ SQL Server Database              │
   └─────────────────────────────────────┘

**Container-First Rehost:**

.. code-block:: bash

   # Smart rehost using containers
   
   # 1. Containerize your existing application
   FROM mcr.microsoft.com/dotnet/aspnet:6.0
   WORKDIR /app
   COPY published-app/ .
   ENTRYPOINT ["dotnet", "MyApp.dll"]
   
   # 2. Deploy to cloud Kubernetes
   kubectl apply -f - <<EOF
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: legacy-app-rehosted
   spec:
     replicas: 3
     selector:
       matchLabels:
         app: legacy-app
     template:
       metadata:
         labels:
           app: legacy-app
       spec:
         containers:
         - name: app
           image: myregistry/legacy-app:v1.0
           ports:
           - containerPort: 80
   EOF

**Benefits:**

- Fastest migration path
- Minimal risk and disruption
- Immediate cloud benefits (scaling, reliability)
- Good starting point for further optimization

**Best for:**

- Legacy applications
- Quick cloud adoption
- Proof of concept migrations
- Applications with minimal changes needed

=======================================
2. Replatform (Lift, Tinker, and Shift)
=======================================

**What it means:** Make a few cloud optimizations without changing core architecture

.. code-block:: text

   Before (On-premises):
   ┌─────────────────────────────────────┐
   │ Application Server                  │
   │ ├─ Self-managed database            │
   │ ├─ File storage on local disk       │
   │ └─ Manual backups                   │
   └─────────────────────────────────────┘
           │ (Replatform)
           ▼
   ┌─────────────────────────────────────┐
   │ Cloud Application                   │
   │ ├─ Managed cloud database (RDS/SQL) │
   │ ├─ Cloud object storage (S3/Blob)   │
   │ └─ Automated backups                │
   └─────────────────────────────────────┘

**Container Replatform Example:**

.. code-block:: yaml

   # Original: Single container with embedded database
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: monolith-app
   spec:
     template:
       spec:
         containers:
         - name: app
           image: myapp:v1.0
           env:
           - name: DB_HOST
             value: "localhost"  # Embedded database
   
   ---
   # Replatformed: Use cloud managed database
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: replatformed-app
   spec:
     template:
       spec:
         containers:
         - name: app
           image: myapp:v1.1  # Minor changes for cloud DB
           env:
           - name: DB_HOST
             value: "my-cluster.cluster-xyz.us-west-2.rds.amazonaws.com"
           - name: DB_USER
             valueFrom:
               secretKeyRef:
                 name: db-credentials
                 key: username
           - name: DB_PASSWORD
             valueFrom:
               secretKeyRef:
                 name: db-credentials
                 key: password

**Cloud Services to Adopt:**

.. code-block:: text

   Replace Self-Managed → Use Cloud Managed
   
   ┌─────────────────────────────────────┐
   │ Database servers                    │ → RDS, Azure SQL, Cloud SQL
   │ File servers                        │ → S3, Blob Storage, Cloud Storage
   │ Message queues                      │ → SQS, Service Bus, Pub/Sub
   │ Caching servers                     │ → ElastiCache, Redis, Memorystore
   │ Load balancers                      │ → ALB, Azure LB, Cloud Load Balancing
   │ Monitoring systems                  │ → CloudWatch, Azure Monitor, Cloud Monitoring
   └─────────────────────────────────────┘

**Benefits:**

- Reduced operational overhead
- Better reliability and security
- Cost optimization through managed services
- Foundation for further modernization

==========================
3. Refactor (Re-architect)
==========================

**What it means:** Redesign applications to be cloud-native

.. code-block:: text

   Before (Monolith):
   ┌─────────────────────────────────────┐
   │ Single Large Application            │
   │ ├─ User Management                  │
   │ ├─ Product Catalog                  │
   │ ├─ Order Processing                 │
   │ ├─ Payment System                   │
   │ └─ Notifications                    │
   └─────────────────────────────────────┘
           │ (Refactor)
           ▼
   ┌─────────────────────────────────────┐
   │ Microservices Architecture          │
   │ ┌─────────┐ ┌─────────┐ ┌─────────┐ │
   │ │  User   │ │Product  │ │ Order   │ │
   │ │ Service │ │Catalog  │ │Processing│ │
   │ └─────────┘ └─────────┘ └─────────┘ │
   │ ┌─────────┐ ┌─────────────────────┐ │
   │ │Payment  │ │   Notifications     │ │
   │ │Service  │ │     Service         │ │
   │ └─────────┘ └─────────────────────┘ │
   └─────────────────────────────────────┘

**Microservices with Kubernetes:**

.. code-block:: yaml

   # User Service
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: user-service
   spec:
     replicas: 3
     template:
       spec:
         containers:
         - name: user-service
           image: myapp/user-service:v2.0
           ports:
           - containerPort: 8080
           env:
           - name: DATABASE_URL
             value: "postgresql://user-db:5432/users"
   
   ---
   # Product Catalog Service
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: catalog-service
   spec:
     replicas: 5  # Can scale independently
     template:
       spec:
         containers:
         - name: catalog-service
           image: myapp/catalog-service:v2.0
           ports:
           - containerPort: 8080
           env:
           - name: CACHE_URL
             value: "redis://catalog-cache:6379"

**Cloud-Native Patterns to Adopt:**

.. code-block:: text

   Traditional Patterns → Cloud-Native Patterns
   
   ┌─────────────────────────────────────┐
   │ Scheduled cron jobs                 │ → Serverless functions (Lambda, Cloud Functions)
   │ Background workers                  │ → Event-driven processing (SQS, Pub/Sub)
   │ Session storage                     │ → Stateless with external state (Redis)
   │ File uploads                        │ → Direct-to-cloud storage (S3, Blob)
   │ Email sending                       │ → Cloud email services (SES, SendGrid)
   │ Log files                           │ → Centralized logging (CloudWatch, Stackdriver)
   └─────────────────────────────────────┘

**Benefits:**

- Maximum cloud benefits
- Better scalability and resilience
- Faster feature development
- Cost optimization through auto-scaling

====================
4. Retire (Turn Off)
====================

**What it means:** Shut down applications that are no longer needed

.. code-block:: text

   Application Portfolio Analysis:
   
   ┌─────────────────────────────────────┐
   │ Legacy System A                     │ → Active users: 5, Usage: Low
   │ Legacy System B                     │ → Duplicate functionality  
   │ Legacy System C                     │ → Regulatory requirement ended
   │ Legacy System D                     │ → Replaced by SaaS solution
   └─────────────────────────────────────┘
           │ (Retire)
           ▼
   ┌─────────────────────────────────────┐
   │ Cost Savings: $50,000/year          │
   │ Reduced complexity                  │
   │ Security risk reduction             │
   │ Focus on valuable systems           │
   └─────────────────────────────────────┘

**Smart Retirement Process:**

.. code-block:: bash

   # 1. Identify retirement candidates
   kubectl get deployments --all-namespaces
   kubectl top pods --all-namespaces  # Check resource usage
   
   # 2. Analyze usage patterns
   # Check application logs and metrics
   
   # 3. Graceful shutdown
   kubectl scale deployment legacy-app --replicas=0
   # Monitor for any issues
   
   # 4. Data archival
   kubectl create job data-export --image=data-exporter:latest
   
   # 5. Complete removal
   kubectl delete deployment legacy-app
   kubectl delete service legacy-app

**Benefits:**

- Immediate cost reduction
- Reduced security surface
- Simplified architecture
- Focus resources on valuable systems

=======================
5. Retain (Keep as is)
=======================

**What it means:** Keep applications on-premises for specific reasons

.. code-block:: text

   Valid Reasons to Retain:
   
   - Regulatory requirements (data locality)
   - High-performance computing needs
   - Legacy systems too risky to move
   - Very low usage (not worth migrating)
   - Pending retirement in near future
   - Custom hardware dependencies

**Hybrid Architecture:**

.. code-block:: yaml

   # Cloud application connecting to on-premises
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: hybrid-app
   spec:
     template:
       spec:
         containers:
         - name: web-app
           image: myapp/web:v3.0
           env:
           - name: LEGACY_SYSTEM_URL
             value: "https://onprem.company.com/api"
           - name: CLOUD_DB_URL
             value: "postgresql://cloud-db:5432/myapp"

**Benefits:**
- Reduced migration risk
- Compliance maintenance
- Cost control for low-value systems
- Gradual migration approach

=======================
6. Repurchase (Buy New)
=======================

**What it means:** Replace with cloud-native or SaaS solutions

.. code-block:: text

   Replace Custom Solutions → Use SaaS/Cloud Services
   
   ┌─────────────────────────────────────┐
   │ Custom email server                 │ → Google Workspace, Office 365
   │ Custom CRM system                   │ → Salesforce, HubSpot
   │ Custom monitoring                   │ → DataDog, New Relic
   │ Custom CI/CD system                 │ → GitHub Actions, GitLab CI
   │ Custom backup solution              │ → Cloud backup services
   └─────────────────────────────────────┘

**Integration with Containers:**

.. code-block:: yaml

   # Your application integrating with SaaS
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: modern-app
   spec:
     template:
       spec:
         containers:
         - name: app
           image: myapp:v4.0
           env:
           # Use SaaS services instead of self-hosted
           - name: EMAIL_SERVICE_URL
             value: "https://api.sendgrid.com/v3"
           - name: CRM_API_URL
             value: "https://api.salesforce.com"
           - name: MONITORING_ENDPOINT
             value: "https://api.datadoghq.com"

**Benefits:**

- Reduced maintenance overhead
- Professional support and SLAs
- Regular feature updates
- Better security and compliance

============================
Migration Strategy Framework
============================

**Phase-Based Approach:**

.. code-block:: text

   Phase 1: Foundation (Months 1-3)
   ┌─────────────────────────────────────┐
   │ Set up cloud accounts and billing   │
   │ Establish network connectivity      │
   │ Migrate development environments    │
   │ Train team on cloud basics          │
   │ Containerize applications locally   │
   └─────────────────────────────────────┘
   
   Phase 2: Quick Wins (Months 3-6)
   ┌─────────────────────────────────────┐
   │ Rehost non-critical applications    │
   │ Migrate test environments           │
   │ Set up monitoring and logging       │
   │ Implement backup strategies         │
   │ Deploy containers to cloud          │
   └─────────────────────────────────────┘
   
   Phase 3: Core Systems (Months 6-12)
   ┌─────────────────────────────────────┐
   │ Replatform key applications         │
   │ Migrate production databases        │
   │ Implement auto-scaling              │
   │ Optimize costs and performance      │
   │ Establish CI/CD pipelines           │
   └─────────────────────────────────────┘
   
   Phase 4: Optimization (Months 12+)
   ┌─────────────────────────────────────┐
   │ Refactor to microservices           │
   │ Implement serverless functions      │
   │ Advanced security and compliance    │
   │ Multi-region deployments            │
   │ Cloud-native architecture           │
   └─────────────────────────────────────┘

==================================
Container-First Migration Benefits
==================================

**Why Start with Containers:**

.. code-block:: text

   Traditional Migration Challenges:

   - "Works on my machine" syndrome
   - Environment configuration drift
   - Complex application dependencies
   - Difficult rollbacks
   - Vendor lock-in concerns
   
   Container-First Advantages:
   
   + Consistent environments everywhere
   + Simplified dependency management
   + Easy rollbacks and blue-green deployments
   + Cloud portability (avoid lock-in)
   + Kubernetes works on all clouds

**Migration Workflow with Containers:**

.. code-block:: bash

   # 1. Containerize locally
   docker build -t myapp:v1.0 .
   docker run -p 8080:8080 myapp:v1.0
   
   # 2. Test with docker-compose
   docker-compose up -d
   # Validate functionality
   
   # 3. Deploy to local Kubernetes
   kubectl apply -f k8s/
   kubectl port-forward service/myapp 8080:80
   
   # 4. Push to cloud registry
   docker push myregistry.azurecr.io/myapp:v1.0
   
   # 5. Deploy to cloud Kubernetes
   kubectl apply -f k8s/
   kubectl get pods  # Same commands work everywhere!

============================
Risk Management and Rollback
============================

**Migration Risk Mitigation:**

.. code-block:: yaml

   # Blue-Green Deployment for Safe Migration
   apiVersion: argoproj.io/v1alpha1
   kind: Rollout
   metadata:
     name: safe-migration
   spec:
     replicas: 5
     strategy:
       blueGreen:
         activeService: myapp-active
         previewService: myapp-preview
         autoPromotionEnabled: false  # Manual approval
         scaleDownDelaySeconds: 30
         prePromotionAnalysis:
           templates:
           - templateName: success-rate
           args:
           - name: service-name
             value: myapp-preview
     template:
       spec:
         containers:
         - name: myapp
           image: myapp:v2.0  # New cloud-optimized version

**Rollback Strategy:**

.. code-block:: bash

   # Always have a rollback plan
   
   # 1. Tag known good versions
   docker tag myapp:v1.0 myapp:stable
   
   # 2. Quick rollback capability
   kubectl rollout undo deployment/myapp
   
   # 3. Database migration rollback scripts
   kubectl create configmap rollback-scripts \
     --from-file=rollback.sql
   
   # 4. Monitor key metrics during migration
   kubectl apply -f monitoring/alerts.yaml

==================================
Cost Optimization During Migration
==================================

**Smart Cost Management:**

.. code-block:: text

   Development Environment Cost Optimization:
   
   ┌─────────────────────────────────────┐
   │ Auto-shutdown non-production        │
   │ ├─ Weekends: Scale to 0             │
   │ ├─ Nights: Scale down 50%           │
   │ └─ Use spot/preemptible instances   │
   ├─────────────────────────────────────┤
   │ Right-size resources                │
   │ ├─ Start small, scale up if needed  │
   │ ├─ Monitor actual usage patterns    │
   │ └─ Use horizontal pod autoscaling   │
   ├─────────────────────────────────────┤
   │ Use cloud-native services           │
   │ ├─ Managed databases                │
   │ ├─ Serverless for batch jobs        │
   │ └─ Object storage for static files  │
   └─────────────────────────────────────┘

.. note::

   **Container Advantage in Migration:**
   
   Your containerization skills make cloud migration much easier:
   
   - **Portability**: Same containers work on any cloud
   - **Consistency**: No "works on my machine" problems
   - **Rollback**: Easy to revert to previous versions
   - **Testing**: Identical environments for dev/test/prod
   - **Skills Transfer**: Kubernetes knowledge applies everywhere
   
   Start containerizing NOW, even before choosing your cloud provider!