This chapter covers designing migration solutions in Microsoft Azure, a critical skill for the AZ-305 exam. Migration questions appear in approximately 15-20% of the exam, focusing on assessing on-premises environments, selecting appropriate migration tools, and planning cutover strategies. You will learn the Azure Migrate framework, replication methods, and how to choose between rehost, refactor, rearchitect, and rebuild strategies. By mastering these concepts, you can design cost-effective, minimal-downtime migrations that align with business requirements.
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Imagine you are moving from a small apartment to a larger house. You have many items—furniture, boxes, appliances—that need to be relocated. A professional moving company offers a structured process: First, they assess your current apartment (discovery) to inventory everything and identify fragile or hazardous items. Then, they plan the move: they decide which truck to use, how to pack items, and the route to the new house (assessment and planning). Next, they pack and load everything onto the truck (migration), ensuring each item is secured and labeled. During transit, they may use multiple trips if the truck is too small (replication) or a single large truck for a big move (bulk transfer). Upon arrival, they unload and unpack, verifying nothing is broken (testing and cutover). Finally, they return to the old apartment to clean and hand over keys (decommissioning). If they find an item they missed, they go back to retrieve it (incremental sync). This mirrors Azure migration: assess on-premises environment with Azure Migrate, plan using Azure Migrate assessments, replicate using Azure Site Recovery or Azure Database Migration Service, test cutover in a staging environment, then migrate and decommission on-premises resources.
1. Overview of Azure Migration Strategy
Migrating workloads to Azure is a structured process governed by the Microsoft Cloud Adoption Framework for Azure. The framework defines four phases: Assess, Migrate, Optimize, and Secure & Manage. The AZ-305 exam focuses heavily on the Assess and Migrate phases. The core goal is to move on-premises workloads (VMs, databases, applications) to Azure with minimal disruption, using tools like Azure Migrate, Azure Site Recovery (ASR), and Azure Database Migration Service (DMS).
The exam expects you to understand the five Rs of migration: Rehost (lift-and-shift), Refactor (move to PaaS), Rearchitect (change architecture for cloud-native), Rebuild (rewrite from scratch), and Replace (use SaaS). Each R has different tooling, cost, and effort implications. For example, rehost uses ASR for VMs, while refactor uses DMS for databases.
2. Azure Migrate: The Central Hub
Azure Migrate is the primary assessment and migration tool. It provides a unified hub to discover, assess, and migrate servers, databases, and web apps. Key components: - Azure Migrate: Discovery and Assessment: Discovers on-premises VMs using the Azure Migrate appliance (a lightweight OVA/OVA for VMware, Hyper-V, or physical servers). The appliance continuously sends performance data to Azure. - Azure Migrate: Server Migration: Handles migration of VMs to Azure using agentless or agent-based replication (leveraging ASR). - Azure Migrate: Database Assessment: Integrates with DMS to assess SQL Server and other databases. - Azure Migrate: Web App Assessment: Assesses ASP.NET and Java web apps for migration to Azure App Service.
The appliance collects data for at least 30 days for performance-based assessments. It uses dependency visualization (via the Microsoft Monitoring Agent and Dependency Agent) to map inter-server dependencies. This is critical for planning migration groups.
3. Assessment: Sizing and Cost Estimation
During assessment, Azure Migrate creates assessment groups (collections of VMs to be migrated together). Two sizing methods: - As on-premises: Uses on-premises configuration (CPU, memory, disk) to recommend Azure VM SKUs. - Performance-based: Uses historical utilization (CPU, memory, disk IOPS, throughput) to right-size Azure VMs. This often results in smaller, cheaper SKUs.
Assessment outputs include: - Azure VM readiness: Indicates if a VM is ready, has compatibility issues (e.g., unsupported OS, disk size > 4 TB), or needs conditional changes. - Monthly cost estimate: Based on Azure Reserved Instances or Pay-As-You-Go pricing. - Storage type recommendation: Managed disks (Standard HDD, Standard SSD, Premium SSD) based on disk IOPS and throughput. - Network bandwidth estimation: For planning data transfer.
4. Replication Methods: Agentless vs. Agent-based
For VM migration, Azure Site Recovery supports two replication modes:
Agentless replication (for VMware VMs):
Uses VMware snapshots to replicate data directly from VMware to Azure.
No agent installed on VMs.
Supports up to 500 VMs per appliance.
Replication interval: 5 minutes (default), can be set to 1, 5, or 15 minutes.
Requires VMware vCenter Server (version 5.5 or later) and ESXi hosts.
Limitations: Only supports VMware VMs; cannot replicate physical servers; requires a separate configuration server appliance.
Agent-based replication (for physical servers, Hyper-V, and VMware):
Installs the Azure Site Recovery Mobility Service agent on each VM.
Supports both Windows and Linux.
Replication interval: 5 minutes (default) for Hyper-V; for VMware/physical, it uses continuous replication with RPO as low as 30 seconds.
Can replicate to a cache storage account in the source region to minimize impact on production.
Requires a process server (can be on-premises or in Azure) to handle replication traffic.
5. Migration Phases: Test, Cutover, and Decommission
Migration follows a phased approach:
Test migration:
Replicates VMs to a test VNet in Azure to validate functionality without impacting production.
Uses the same replicated data as the actual migration.
After testing, cleanup the test VM to free resources.
Cutover:
The final step where you stop replication, fail over to Azure, and start the VM.
For agentless replication, you must shut down the on-premises VM to ensure data consistency.
For agent-based, you can perform a planned failover with minimal downtime.
After cutover, you can commit the migration (makes Azure VM the primary) or roll back (if issues arise).
Decommission:
After successful cutover, decommission on-premises resources.
Remove the Azure Migrate appliance and stop replication.
Update DNS, backup policies, and monitoring to point to Azure.
6. Database Migration: Azure Database Migration Service (DMS)
For migrating databases to Azure, DMS provides offline (one-time) and online (minimal downtime) migrations.
Online migration:
Uses transactional replication (for SQL Server) or log shipping (for PostgreSQL, MySQL) to continuously sync changes.
Requires a Premium tier DMS instance.
Supports SQL Server, Azure SQL Database, Azure SQL Managed Instance, PostgreSQL, MySQL, and MongoDB.
During cutover, stop writes to source, apply final changes, and switch connection strings.
Offline migration:
Uses a full backup and restore.
Downtime is the time to restore the backup.
Supported for smaller databases (< 2 TB) or when downtime is acceptable.
Key settings: - Source SQL Server: Must be at least SQL Server 2005. - Target Azure SQL Database: Use the DTU or vCore purchasing model. - Compatibility level: DMS can upgrade the database compatibility level during migration.
7. Storage Migration: Azure Storage Migration Service
For file shares and blob storage, use Azure Storage Mover (preview) or AzCopy.
Azure Storage Mover:
Agent-based tool for migrating file shares (SMB) to Azure Files or Azure Blob Storage.
Supports incremental sync.
Can run on-premises or on an Azure VM.
AzCopy:
Command-line tool for copying blobs or files to Azure Storage.
Supports parallel transfers and resume on failure.
Example: azcopy copy "C:\\mydata" "https://mystorageaccount.blob.core.windows.net/mycontainer?<SAS-token>" --recursive
8. Choosing the Right Migration Strategy
The exam tests your ability to match business requirements to migration strategies:
| Requirement | Recommended Strategy | Tool | |-------------|----------------------|------| | Minimal downtime | Online migration (ASR, DMS online) | Azure Site Recovery, DMS online | | Low cost | Rehost (lift-and-shift) | ASR agentless | | Modernize application | Refactor (move to PaaS) | DMS, Azure App Service migration assistant | | Complex dependencies | Rehost with dependency mapping | Azure Migrate dependency visualization | | Compliance/security | Rehost with Azure Policy and Blueprints | Azure Migrate, Azure Policy |
9. Migration of Windows Server and SQL Server
Azure has specific programs for migrating Windows Server and SQL Server workloads:
Azure Hybrid Benefit: Allows you to use on-premises Windows Server or SQL Server licenses with Software Assurance to reduce Azure VM costs.
Extended Security Updates (ESU): For Windows Server 2008/R2 and 2012/R2, you can get free extended security updates when migrated to Azure.
SQL Server 2008/R2: End of support, but Azure SQL Managed Instance provides automatic upgrades.
10. Testing and Validation
Before final cutover, validate: - Performance: Run load tests on Azure VMs. - Connectivity: Ensure VMs can reach required on-premises resources via VPN or ExpressRoute. - Backup: Configure Azure Backup for migrated VMs. - Monitoring: Enable Azure Monitor and Application Insights.
Use Azure Test Plans (in Azure DevOps) for automated testing if part of a larger CI/CD pipeline.
11. Post-Migration Optimization
After migration, optimize: - Right-size VMs: Use Azure Advisor recommendations. - Reserved Instances: Purchase 1- or 3-year reservations for stable workloads. - Storage tiering: Move infrequently accessed data to cool or archive tiers. - Auto-shutdown: Schedule shutdown for non-production VMs.
12. Common Pitfalls and Exam Traps
Confusing assessment and migration: Assessment uses Azure Migrate; migration uses ASR or DMS. Azure Migrate does not perform migration itself.
Overlooking dependency mapping: Without it, you may migrate VMs in wrong order, causing application failures.
Choosing offline migration for large databases: For databases > 2 TB, online migration is recommended to avoid long downtime.
Ignoring Azure Hybrid Benefit: Can save up to 40% on Windows Server and SQL Server costs.
Forgetting to decommission on-premises resources: Leads to unnecessary licensing costs.
Discover on-premises environment
Deploy the Azure Migrate appliance (OVA for VMware, VHDX for Hyper-V, or script for physical servers) in your on-premises environment. The appliance runs on a Windows Server 2016 VM and uses the VMware vCenter Server API (for VMware) or WMI (for Hyper-V) to collect inventory data. It sends metadata and performance data to Azure Migrate project over HTTPS (port 443). For physical servers, install the Azure Migrate agent on each server. The appliance collects data continuously; for performance-based assessments, wait at least 30 days.
Assess and group workloads
In Azure Migrate, create assessment groups. Use dependency visualization (install Microsoft Monitoring Agent and Dependency Agent on VMs) to map inter-VM dependencies. This reveals which VMs communicate with each other and must be migrated together. Create groups based on application tiers (web, app, database). Run an assessment to get Azure VM SKU recommendations, cost estimates, and readiness status. Review any compatibility issues (e.g., unsupported OS, disk size > 4 TB).
Replicate data to Azure
Set up replication using Azure Site Recovery. For VMware VMs with agentless replication, deploy a configuration server and process server (can be combined). For agent-based replication, install Mobility Service on each VM. Configure replication settings: target region, subscription, resource group, virtual network, and storage account (cache storage account in source region). Replication begins; initial sync transfers full disk data, then ongoing replication sends changes every 5 minutes (default). Monitor replication health in ASR dashboard.
Test migration in staging environment
Before cutover, perform a test failover to a test VNet in Azure. This creates a replica of the VM using the same replicated data but isolated from production. Validate that the test VM boots, applications work, and network connectivity is correct. After testing, clean up the test VM to avoid charges. Repeat until satisfied. Test migration confirms that the migration plan works and identifies any issues with application configuration or network settings.
Cutover and decommission
For the final cutover, stop the on-premises VM (for agentless) or perform a planned failover (for agent-based). In ASR, click 'Failover' and select the latest recovery point (latest, latest consistent, or custom). After failover, verify the Azure VM is running and accessible. Once confirmed, click 'Commit' to finalize. Then, decommission the on-premises VM: remove from vCenter, delete backups, and update DNS. Finally, clean up the Azure Migrate appliance and stop replication.
Enterprise Scenario 1: Large-Scale VMware Migration to Azure
A global retailer with 2,000 VMware VMs across 3 data centers needed to migrate to Azure within 6 months. They used Azure Migrate for discovery and assessment. Dependency mapping revealed that many VMs had inter-dependencies, so they grouped them into 50 migration waves. They chose agentless replication for 90% of VMs (VMware) and agent-based for the remaining 10% (physical servers running legacy OS). Each wave included a test migration to a staging VNet, followed by cutover during a maintenance window. They used Azure Site Recovery with a recovery point objective (RPO) of 5 minutes and recovery time objective (RTO) of 15 minutes. After migration, they decommissioned on-premises infrastructure, saving 40% in operational costs. A common issue was network bandwidth saturation during initial sync; they throttled replication to 100 Mbps per appliance to avoid impact on production traffic.
Enterprise Scenario 2: SQL Server Database Migration with Minimal Downtime
A financial services company needed to migrate a 5 TB SQL Server 2012 database to Azure SQL Managed Instance with less than 1 hour of downtime. They used Azure Database Migration Service (DMS) with online migration mode. They set up transactional replication to continuously sync changes. The source database had high transaction volume, so they used a Premium DMS instance and a cache storage account in the same region as the source to reduce latency. During the cutover, they stopped writes to the source, applied the final log backup, and switched the connection string. The entire cutover took 45 minutes. Post-migration, they used Azure Hybrid Benefit for SQL Server to reduce licensing costs. A challenge was that the source database had a very large transaction log; they had to ensure enough disk space for log shipping.
Scenario 3: Physical Server Migration with Agent-Based Replication
A manufacturing company had 50 physical servers running Windows Server 2008 R2 (extended support ended). They needed to migrate to Azure VMs to get free Extended Security Updates (ESU). Since physical servers cannot use agentless replication, they installed the Mobility Service agent on each server and used a process server (an Azure VM) to handle replication. They set up a site-to-site VPN between on-premises and Azure for secure data transfer. The migration was performed in waves of 10 servers per week. They encountered an issue where the Mobility Service agent failed to install on servers with insufficient memory (< 2 GB). They upgraded those servers temporarily. After migration, they enabled Azure Backup and configured auto-shutdown for non-production servers to save costs.
The AZ-305 exam tests migration under objective 4.3 Design a migration solution. You must understand the complete migration lifecycle and tool selection. Key areas:
1. Assessment vs. Migration Tools: The exam often presents a scenario where you need to assess on-premises VMs. Candidates incorrectly choose Azure Site Recovery (ASR) for assessment. Correct: Use Azure Migrate for assessment; ASR is for replication and migration. Remember: Azure Migrate does NOT perform migration; it only assesses and provides recommendations.
2. Replication Methods: The exam tests when to use agentless vs. agent-based replication. Common trap: Choosing agentless for physical servers. Correct: Agentless is only for VMware VMs. Agent-based supports physical servers and Hyper-V. Also, agentless requires a configuration server; agent-based requires Mobility Service on each VM.
3. Database Migration Modes: The exam asks about offline vs. online migration. Trap: Selecting offline for a mission-critical database needing minimal downtime. Correct: Online migration uses transactional replication and allows near-zero downtime. Offline is for smaller databases or acceptable downtime.
4. Migration Strategy Selection: Given business requirements (e.g., minimal cost, minimal downtime, modernize), you must pick the right R. Trap: Choosing rehost when the requirement is to modernize (use PaaS). Correct: Rehost is lift-and-shift; refactor moves to PaaS (e.g., Azure SQL Database).
5. Specific Numbers and Terms:
Azure Migrate assessment: minimum 30 days for performance-based.
Agentless replication: supports up to 500 VMs per appliance.
ASR default replication interval: 5 minutes (Hyper-V); for VMware, continuous replication with RPO as low as 30 seconds.
DMS online migration requires Premium tier.
Azure Hybrid Benefit: for Windows Server and SQL Server with Software Assurance.
Extended Security Updates: free for Windows Server 2008/R2 and 2012/R2 when migrated to Azure.
6. How to Eliminate Wrong Answers:
If the question says 'assess on-premises', eliminate any answer that mentions ASR or DMS.
If the question says 'migrate with minimal downtime', eliminate offline migration options.
If the question says 'physical server', eliminate agentless replication.
If the question says 'modernize application', eliminate rehost (lift-and-shift).
If the question mentions 'cost savings', look for Azure Hybrid Benefit or Reserved Instances.
Azure Migrate is for assessment only; use Azure Site Recovery for VM migration and DMS for database migration.
Agentless replication is for VMware only; agent-based for physical and Hyper-V.
Online database migration uses transactional replication for minimal downtime; offline is for smaller databases with acceptable downtime.
Performance-based assessments require at least 30 days of data collection.
Azure Hybrid Benefit reduces costs for Windows Server and SQL Server with Software Assurance.
Extended Security Updates are free for Windows Server 2008/R2 and 2012/R2 when migrated to Azure.
Dependency mapping is critical to identify inter-VM dependencies and group VMs correctly.
These come up on the exam all the time. Here's how to tell them apart.
Agentless Replication
Only supports VMware VMs
No agent installed on VMs
Uses VMware snapshots for replication
Supports up to 500 VMs per appliance
Requires VMware vCenter Server and ESXi hosts
Agent-based Replication
Supports physical servers, Hyper-V, and VMware
Requires Mobility Service agent on each VM
Uses continuous replication (RPO as low as 30 seconds)
Scalable to thousands of VMs with multiple process servers
Works without VMware infrastructure
Mistake
Azure Migrate can perform the actual migration of VMs.
Correct
Azure Migrate is an assessment tool only. It discovers and assesses on-premises workloads but does not perform migration. Migration is done by Azure Site Recovery (for VMs) or Azure Database Migration Service (for databases).
Mistake
Agentless replication can be used for physical servers.
Correct
Agentless replication is only supported for VMware VMs. Physical servers and Hyper-V VMs require agent-based replication, which installs the Mobility Service on each server.
Mistake
Offline database migration provides minimal downtime.
Correct
Offline migration requires taking the database offline to perform a full backup and restore, resulting in significant downtime. Online migration uses transactional replication to synchronize changes with near-zero downtime.
Mistake
You need to purchase Extended Security Updates (ESU) for Windows Server 2008/R2 when migrated to Azure.
Correct
Windows Server 2008/R2 and 2012/R2 receive free Extended Security Updates when migrated to Azure. No additional purchase is required, but you must migrate before the end-of-support date.
Mistake
Azure Hybrid Benefit only applies to Windows Server, not SQL Server.
Correct
Azure Hybrid Benefit applies to both Windows Server and SQL Server. It allows you to use on-premises licenses with Software Assurance to reduce Azure costs.
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
Azure Migrate is an assessment tool that discovers on-premises servers and provides recommendations for Azure VM sizing and cost. It does not perform migration. Azure Site Recovery (ASR) is the tool used for actual replication and migration of VMs to Azure. After assessment, you use ASR to replicate, test failover, and cutover. Think of Azure Migrate as the planning phase and ASR as the execution phase.
No. Agentless replication is only supported for VMware VMs. For physical servers, you must use agent-based replication, which involves installing the Azure Site Recovery Mobility Service agent on each server. This agent handles data replication to Azure.
Choose online migration when you need minimal downtime (e.g., for a production database). It uses transactional replication to keep the source and target synchronized, allowing a short cutover window. Choose offline migration when downtime is acceptable (e.g., for a development database) or when the database is small (< 2 TB) and you want a simpler process. Offline involves a full backup and restore, which can take hours for large databases.
Azure Hybrid Benefit allows you to use your on-premises Windows Server or SQL Server licenses with Software Assurance to reduce Azure costs. For Windows Server, you pay only the base compute rate (no Windows license cost). For SQL Server, you can choose a lower-priced Azure SQL Database tier. When planning migration, assess if your licenses qualify to optimize costs.
No. If you migrate Windows Server 2008/R2 or 2012/R2 to Azure before their end-of-support dates, you get free Extended Security Updates for three years after the end-of-support date. This applies to both VMs and Azure SQL Managed Instance. No additional purchase or configuration is needed.
Dependency visualization maps network connections between on-premises servers, showing which servers communicate with each other. It is important because it helps you identify application dependencies and group servers that must be migrated together. Without it, you might migrate a web server before the database server, causing application failures.
Azure Migrate recommends collecting performance data for at least 30 days to capture peak utilization patterns. This ensures the assessment recommends appropriately sized Azure VMs. Shorter periods may underestimate resource needs, leading to under-provisioned VMs.
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