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Migration Strategies

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Cloud migration is the process of moving applications, data, and infrastructure from on-premises environments to AWS. The 7 Rs framework helps select the right migration strategy for each workload.

The 7 Rs

Strategy	Description	When to Use
Retire	Decommission applications no longer needed	Eliminate waste, reduce cost
Retain	Keep applications on-premises	Compliance, latency, or technical debt
Rehost (Lift & Shift)	Move as-is to EC2 or VM Import	Quick wins, minimal changes
Replatform (Lift, Tinker & Shift)	Move with minor optimizations	Migrate to RDS, Elasticache, etc.
Refactor (Re-architect)	Rewrite for cloud-native patterns	Serverless, microservices, containers
Repurchase (Drop & Shop)	Move to SaaS solution	Move CRM to Salesforce, email to SaaS

                        ┌─────────┐
                        │ Current │
                        │ On-Prem │
                        └────┬────┘
                             │
             ┌───────────────┼───────────────┐
             ▼               ▼               ▼
       ┌──────────┐   ┌──────────┐   ┌──────────┐
       │ Rehost   │   │Replatform│   │ Refactor │
       │ (quick)  │   │(moderate)│   │ (best)   │
       └──────────┘   └──────────┘   └──────────┘
       60-80% first    15-25% first    5-15%
       wave            wave            (ongoing)

The 80/20 Rule

Most organizations rehost 60-80% of applications in the first migration wave. Refactoring is reserved for applications that need fundamental architectural changes. Start with rehost, then optimize over time.

Migration Evaluator

AWS Migration Evaluator (formerly TSO Logic) provides a data-driven business case for migration:

# Download the migration evaluator agent
# Install on-premises to collect utilization data

# After assessment, export the report
aws migration-hub create-migration-task \
  --migration-task-name "web-app-migration" \
  --progress-update-stream "web-app-stream" \
  --resource-attribute-list "[{\"ipAddress\":\"10.0.1.50\"}]"

The tool analyzes:

CPU, memory, and disk utilization over time
Network throughput and dependencies
License costs (OS, database, middleware)
Recommended right-sizing in AWS (EC2, RDS)

AWS Application Migration Service (MGN)

MGN (formerly CloudEndure) performs continuous replication for rehost migrations:

    sequenceDiagram
    OnPrem->>Staging: Continuous block-level replication
    Staging-->>OnPrem: Data compressed, encrypted
    Note over OnPrem,Staging: Cutover window
    OnPrem->>OnPrem: Stop application
    OnPrem->>Target: Launch test instance
    Target-->>OnPrem: Verify data consistency
    OnPrem->>Target: Launch production instance
    Target-->>DNS: Update DNS to AWS

# Create an MGN launch template
aws mgn create-launch-configuration-template \
  --template-id "lt-12345" \
  --post-launch-actions "{\"cloudWatchLogGroupId\":\"/aws/mgn\"}"

# List source servers ready for migration
aws mgn describe-source-servers \
  --filters "{\"isArchived\":[\"false\"]}"

Feature	Benefit
Continuous block-level replication	Sub-second RPO
Automated staging area	No data copy during cutover
Non-disruptive testing	Test instances without affecting on-prem
Automated conversion	Boot volumes, drivers, network reconfigured

AWS DataSync

DataSync automates moving data between on-premises storage and AWS:

# Create a DataSync task from NFS to S3
aws datasync create-task \
  --source-location-arn "arn:aws:datasync:us-east-1:123456789012:location/loc-src-123" \
  --destination-location-arn "arn:aws:datasync:us-east-1:123456789012:location/loc-dest-456" \
  --options "PreserveDeletedFiles=REMOVE,VerifyMode=POINT_IN_TIME_CONSISTENT" \
  --name "file-server-migration"

# Start the task
aws datasync start-task-execution --task-arn "arn:aws:datasync:..."

Feature	Capability
Sources	NFS, SMB, HDFS, S3, EFS, FSx
Speed	Up to 10 Gbps per agent
Validation	Automatic checksums, in-flight verification
Filtering	Include/exclude patterns, preserve metadata
Bandwidth limiting	Schedule during off-peak hours

AWS Snowball

Snowball is a physical device for large-scale data transfers when network bandwidth is limited:

Device	Storage	Transfer Speed	Best For
Snowball Edge Storage Optimized	80 TB HDD + 1 TB SSD	100 Gbps	Large datasets, edge computing
Snowball Edge Compute Optimized	42 TB HDD + 7.68 TB SSD	100 Gbps	Edge ML, data processing
Snowmobile	100 PB per truck	1 Tbps (100 Gbps * 10)	Exabyte-scale migrations

# Create a Snowball Edge job
aws snowball create-job \
  --job-type "IMPORT" \
  --resources "{\"s3Resources\":[{\"bucketArn\":\"arn:aws:s3:::migration-data\",\"keyRange\":{\"beginMarker\":\"\",\"endMarker\":\"\"}}]}" \
  --address-id "addr-12345678" \
  --role-arn "arn:aws:iam::123456789012:role/snowball-role" \
  --job-description "Historical data archive migration"

Tip

Use Snowball when the transfer would take more than 1 week over your available bandwidth. Formula: Transfer Time (days) = (Data Size in TB × 8 × 1024) / (Bandwidth in Mbps) / 86400. For 100 TB over 100 Mbps it takes ~95 days — use Snowball.

Migration Planning Checklist

Phase	Activities	Tools
Assess	Discover inventory, analyze utilization, map dependencies	Migration Evaluator, AWS Application Discovery Service
Mobilize	Build landing zone, establish connectivity, train team	AWS Control Tower, Transit Gateway, VPN/Direct Connect
Migrate	Execute migrations wave by wave, test, cut over	MGN, DataSync, DMS, SMS
Operate	Monitor, optimize, decommission legacy	CloudWatch, Cost Explorer, Trusted Advisor

Key Takeaways

The 7 Rs framework guides migration strategy: Rehost (60-80% of apps, quick wins), Replatform (minor optimizations like moving to RDS), Refactor (rewrite for cloud-native), Repurchase (swap to SaaS), Retire (decommission), Retain (keep on-prem), Relocate (move to AWS) — AWS now includes Relocate as an 8th R for moving between hypervisors
Migration Evaluator builds the business case by analyzing on-prem utilization (CPU, memory, disk, network) and rightsizing to EC2/RDS equivalents
Application Migration Service (MGN) provides continuous block-level replication for rehost migrations with sub-second RPO, automated staging, non-disruptive testing, and automated server conversion
DataSync automates data transfer from NFS/SMB/HDFS to AWS at up to 10 Gbps with checksum validation and metadata preservation
Snowball devices transfer 80 TB+ when network bandwidth is insufficient — use the bandwidth formula to decide: transfer time > 1 week means use Snowball
Migration follows four phases: Assess (discovery), Mobilize (landing zone, connectivity), Migrate (waves, test, cut over), Operate (monitor, optimize, decommission)