Part 2 of this two-part series moves from licensing and Active Directory decisions into the hands‑on mechanics you must master to migrate Windows Server workloads to Amazon EC2: choosing the correct virtualization platform and instance family, verifying boot‑mode compatibility (UEFI vs Legacy BIOS), picking and preinstalling the right drivers, and running the AWS validation tools that catch the migration blockers before you hit a production cutover.
Successful Windows Server migrations to Amazon EC2 are not a single command or a single tool — they are a sequence of small, technical validations that together prevent a non‑booting instance, driver incompatibility, or a prolonged replication stall. Two underlying platform facts drive most migration decisions:
Example (Linux shell / PowerShell with AWS CLI configured):
By baking these checks into your migration runbook — and by automating the discovery of instance hypervisor and boot‑mode compatibility — you reduce risk, accelerate cutovers, and create a repeatable migration pipeline that scales beyond individual servers to large enterprise projects.
Source: Amazon Web Services Mastering Windows Server migration to Amazon EC2: Key tactics for success – Part 2 | Amazon Web Services
Background
Successful Windows Server migrations to Amazon EC2 are not a single command or a single tool — they are a sequence of small, technical validations that together prevent a non‑booting instance, driver incompatibility, or a prolonged replication stall. Two underlying platform facts drive most migration decisions:- Modern EC2 instance families are built on the AWS Nitro System, which presents EBS block devices through NVMe and depends on Nitro device drivers in the guest OS. Nitro‑based instances also typically support UEFI booting.
- Older EC2 instance families were implemented atop the Xen hypervisor, which historically used emulated IDE devices early in the boot process and then paravirtualized block drivers (PV) for runtime I/O. Some legacy Windows Server versions (notably older than Windows Server 2012 / 2008 R2) are more likely to be compatible or easier to migrate to Xen‑based instance types.
Overview: The migration mindset
Before you start technical work, adopt a defensive posture: validate early, automate checks, and prefer test migrations. That mindset reduces surprises and shortens the troubleshooting loop during cutover windows.- Validate boot mode, disk layout, and free space on the source OS.
- Decide whether to import images with VM Import/Export or to replicate with AWS Application Migration Service (MGN); pick the validation tool that matches the migration path.
- Ensure required drivers (NVMe/ENA when moving to Nitro) or legacy Xen drivers are present depending on target instance hypervisor.
- Run the validation tools (VM Import Checker or MGN Toolkit) and remediate all critical failures before attempting final import or cutover.
Choosing the right EC2 hypervisor: Xen vs. Nitro
Why the hypervisor matters
The hypervisor (or underlying EC2 platform) is not an abstract preference; it dictates the guest‑level device model, available drivers, and supported boot behavior.- Xen‑based instances (for example older instance families like M4, C4) historically booted from emulated IDE devices and used Xen paravirtualized block drivers for improved I/O after boot. If your Windows Server image predates Nitro awareness (older drivers, older Sysprep handling) it may behave better on Xen‑based types.
- AWS Nitro System instances (M5, C5, M6, C6 families and beyond, and most modern Intel/AMD instance types) expose Amazon EBS volumes through an NVMe interface and rely on Nitro device drivers such as the AWS NVMe and the Elastic Network Adapter (ENA). Nitro also underpins advanced features like NitroTPM and broad UEFI support. Preparing a VM that will run on Nitro therefore usually requires ensuring NVMe and ENA drivers are present or will be installed during provisioning.
How to discover which instance types are Xen or Nitro
Use the EC2 API or AWS CLI to filter instance types by hypervisor. The official AWS CLI command describe-instance-types supports filters such ashypervisor and processor-info.supported-architecture. This is the most reliable way to enumerate instance types in a specific region before you commit to a migration target. Example (Linux shell / PowerShell with AWS CLI configured):
- List Xen instance types (x86_64):
aws ec2 describe-instance-types --filters Name=hypervisor,Values=xen Name=processor-info.supported-architecture,Values=x86_64 --query 'sort_by(InstanceTypes, &InstanceType) - .{InstanceType:InstanceType}' --output table
- List Nitro instance types (x86_64):
aws ec2 describe-instance-types --filters Name=hypervisor,Values=nitro Name=processor-info.supported-architecture,Values=x86_64 --query 'sort_by(InstanceTypes, &InstanceType) - .{InstanceType:InstanceType}' --output table
describe-instance-types command and its filters are documented in the AWS CLI reference and guarantee you inspect actual instance metadata for the region you plan to use. Practical guidance
- Prioritize Xen targets for very old Windows Server versions (Windows Server 2008 R2 and earlier) only when Nitro drivers are missing and Xen instances are available in your chosen region. Note that Xen‑based instance availability varies by AWS region and is not guaranteed in newer regions — always confirm with the CLI or API. This regional availability is dynamic and can change, so treat it as a live check rather than a static rule.
- For Windows Server 2016 and later, plan to target Nitro families where possible because they are the focus of AWS innovation (performance, security features, NitroTPM, UEFI/secure boot) and will give you a longer supported runway.
Boot mode and why it blocks boot
UEFI vs Legacy BIOS: the critical difference
When a VM boots it relies on a firmware interface that the OS expects: UEFI or Legacy BIOS. Amazon EC2 supports both UEFI and Legacy BIOS boot modes, and an AMI includes a boot‑mode parameter that tells EC2 which mode to use at launch. Using the wrong boot mode for a migrated image will cause the instance to fail to boot. AWS provides the ability to create AMIs flagged for UEFI, Legacy BIOS, or UEFI Preferred, and Nitro instance types typically support UEFI.How to determine the boot mode on Windows (exact commands)
On the Windows server you plan to migrate, run an elevated command prompt and use bcdedit to inspect the loader path:- Open an elevated Command Prompt and run:
bcdedit | find "path" - Interpretation:
- If the Windows Boot Loader path ends with \Windows\system32\winload.efi the system boots via UEFI.
- If it ends with \Windows\system32\winload.exe the system boots via Legacy BIOS.
$env:firmware_type or querying WMI (Get-WmiObject -Class Win32_ComputerSystem) also returns firmware type in modern Windows releases. Actionable rule
- If your Windows Server uses UEFI, target a Nitro instance family that supports UEFI boot.
- If your Windows Server uses Legacy BIOS, you can target either Nitro (which supports Legacy BIOS for many instance types) or compatible Xen types — but confirm the resulting AMI boot parameter and instance supported boot modes first. AWS documentation shows the decision matrix (AMI boot parameter, OS boot mode, and instance type support determine the final boot mode).
Driver compatibility: NVMe, ENA, and Xen PV drivers
What to preinstall or verify
- If you plan to use Nitro target instances, ensure the guest OS has drivers for:
- AWS NVMe (EBS over NVMe devices) — this is essential for block device access on many Nitro instance types.
- ENA (Elastic Network Adapter) — for high throughput, low latency networking.
- AWS SSM Agent and other launch‑time tools (EC2Launch/EC2Config on Windows) so the AMI can complete post‑launch initialization.
- If you plan to use Xen targets, verify presence of compatible Xen paravirtual drivers where necessary and that the image boots using the IDE/Legacy device mapping expected by Xen.
How to check and install drivers on Windows
- Confirm ENA/NVMe driver presence by checking Device Manager entries or validating installed drivers via PowerShell.
- For Nitro readiness, AWS documentation recommends preinstalling ENA and NVMe drivers before exporting or replicating images to reduce boot‑time driver installation issues. For Linux, AWS recommends specific NVMe driver packages; for Windows, use Microsoft/WIN32 drivers and AWS tooling delivered in AMIs or documentation.
Validation tools: VM Import Checker and MGN Toolkit
Pick the tool that matches your migration approach
- If you use VM Import/Export to import VM images as AMIs or instances, run the VM Import Checker (a PowerShell tool available via Migration Hub Orchestrator scripts) to validate the source server against VM Import/Export requirements. The VM Import/Export documentation lists key prerequisites and limitations (for example, Windows images require at least 6 GiB free on the root volume and VM Import fails for VMs with more than 21 volumes attached).
- If you use AWS Application Migration Service (MGN) for continuous replication and automated cutover, use the MGN Toolkit (an open‑source set of PowerShell scripts maintained by AWS Labs) to validate prerequisites, post‑migration issues, and replication readiness. The toolkit checks boot mode, free space, BitLocker, certificates, network connectivity to MGN endpoints, and other migration‑specific settings.
What the tools check (representative items)
- Boot mode (UEFI/BIOS), partition style (GPT/MBR), and number of bootable partitions.
- Free root/boot disk space (Windows: at least 6 GiB for VM Import/Export; MGN Toolkit may require smaller free space for driver installs but flags low space).
- Number of attached disks (VM Import/Export fails if >21 volumes).
- DHCP availability and network configuration — VM Import assigns a single NIC and relies on DHCP in imported instances; multiple NICs are not supported by VM Import/Export.
- Presence of required certificates, .NET versions, BitLocker state (MGN Toolkit flags BitLocker as not supported), and antivirus that might block the replication agent.
Running the tools: example snippets
- VM Import Checker (PowerShell): the blog post and the tool bundle provide a script that can be downloaded and executed. The VM Import/Export docs list the exact checks and failure conditions (disk count limits, free space, DHCP, etc.). If any individual test returns FAILED the overall import attempt will also fail until the issue is addressed.
- MGN Toolkit: download from the awslabs GitHub repo (
[url="https://github.com/awslabs/mgn-toolkit"]GitHub - awslabs/mgn-toolkit[/url]), unzip, and run the provided PowerShell entry script. The Toolkit returns colorized statuses (GREEN/YELLOW/RED) and contains targeted checks for replication performance and security posture.
Walkthrough: a recommended pre‑migration sequence
- Inventory and classification
- Catalog OS versions, disk counts, boot mode, application criticality, and dependencies.
- Flag any Windows Server versions older than 2012 R2 for special handling (likely Xen or replatforming).
- Verify boot mode on each Windows server
- Run bcdedit and confirm
winload.efi(UEFI) orwinload.exe(Legacy BIOS). Use PowerShell$env:firmware_typeas a fast check. - Choose target instance family and region
- Use
aws ec2 describe-instance-typeswith--filters Name=hypervisor,Values=nitroorxento enumerate what’s available in the selected region. Confirmsupported-boot-modeandsupported-root-device-type. - Ensure driver compatibility on source
- If Nitro target: install/verify NVMe and ENA drivers (and ensure the SSM agent / EC2Launch will be available to complete post‑launch configuration).
- If Xen target: verify expected Xen drivers are present and that the disk device mapping will match the Xen model.
- Validate with the matching tool
- VM Import path: run VM Import Checker and resolve any FAIL or WARNING items (free space, pagefile placement, disk attachments, DHCP).
- MGN path: run MGN Toolkit and follow remediation suggestions for RED/YELLOW checks.
- Run a test migration
- Use a nonproduction copy or snapshot to import/replicate into a test VPC. Boot the test instance, validate drivers, networking, and application behavior. Don’t skip this step; it surfaces absent drivers, broken services, or licensing agents that depend on hardware IDs.
- Cutover and cleanup
- After successful tests, perform a final replication or image import, run final validation, and cut over traffic. Remove old virtualization agents (VMware Tools, Hyper‑V integration components) if they impact boot or licensing checks, but only after ensuring backups and rollback plans are in place.
Pitfalls, risks, and mitigation strategies
Hidden or dynamic constraints
- Instance family availability by region is dynamic. Older Xen families may be absent in newer regions; Nitro continues to expand. Always treat instance availability as a live, region‑specific check and script
describe-instance-typesinto your validation pipeline.
Driver/boot mismatches
- The most common migration failure modes are missing NVMe/ENA drivers (resulting in no block device access) and incorrect boot mode selection (UEFI vs Legacy BIOS). Run the driver checks and the boot‑mode checks early and treat them as migration blockers.
Disk and network limitations of VM Import/Export
- VM Import/Export has documented limits: Windows images require at least 6 GiB free space on root, and images with more than 21 volumes fail import tasks. Additionally, VM Import assigns a single private IPv4 address and depends on DHCP for address assignment post‑import. Plan for these constraints or use MGN when you need richer migration semantics.
Security and BitLocker
- BitLocker and other disk encryption mechanisms can block migrations. MGN Toolkit flags BitLocker as unsupported — decrypt volumes or plan for an alternative migration method.
Regression in apps expecting hardware identifiers
- Migrated servers present different BIOS GUIDs and hardware IDs in EC2. Any licensing tied to hardware identifiers may need revalidation with vendors — include license remediation as part of the cutover checklist.
Strengths of the recommended approach
- Proactive validation (VM Import Checker / MGN Toolkit) removes the biggest unknowns before an import or replication begins, reducing cutover windows and unexpected downtime.
- Targeting Nitro families for supported Windows versions yields better long‑term support, security features (NitroTPM, measured boot), and performance due to modern networking (ENA) and storage (NVMe) drivers.
- Using the AWS CLI to enumerate real instance metadata ensures the migration design reflects actual region capability rather than stale documentation. Automating these checks in CI/CD or migration pipelines pays off immediately.
Final checklist (ready to paste into runbooks)
- [ ] Inventory OS versions and dependencies; tag Windows versions older than 2012 R2 for careful review.
- [ ] Run bcdedit (or PowerShell checks) and record boot mode (UEFI or Legacy BIOS) for each server.
- [ ] Query region instance types via
aws ec2 describe-instance-typesand confirm hypervisor and supported boot modes for planned targets. - [ ] Verify NVMe/ENA drivers or Xen PV drivers are present; stage driver installs into scripts where needed.
- [ ] If using VM Import/Export: run VM Import Checker and remediate ALL FAIL results; ensure root has >= 6 GiB free and <= 21 volumes are attached.
- [ ] If using MGN: run the MGN Toolkit from the awslabs repo and remediate RED/YELLOW checks; validate replication bandwidth and disk write performance.
- [ ] Execute a test migration in a nonproduction VPC, validate boot, drivers, and application functionality.
- [ ] Confirm licensing and vendor product activation post‑migration; address machine identity or BIOS GUID changes as needed.
- [ ] Schedule a short maintenance window and roll‑back plan for final cutover.
Conclusion
Migrating Windows Server workloads to Amazon EC2 is tractable when you treat it as a series of explicit, repeatable validations rather than a single lift‑and‑shift event. The most common and preventable failures — missing NVMe/ENA drivers, incorrect boot mode, insufficient free space, or exceeding VM Import volume limits — are all detectable with the right tools and checks: run bcdedit and the validation scripts early, enumerate instance types with the AWS CLI, and use the VM Import Checker or the MGN Toolkit appropriate to your chosen migration method. The payoff is straightforward: fewer failed boots, shorter cutover windows, and a clear path to modernization on Nitro‑based instances where your Windows workloads can take advantage of improved security and performance features.By baking these checks into your migration runbook — and by automating the discovery of instance hypervisor and boot‑mode compatibility — you reduce risk, accelerate cutovers, and create a repeatable migration pipeline that scales beyond individual servers to large enterprise projects.
Source: Amazon Web Services Mastering Windows Server migration to Amazon EC2: Key tactics for success – Part 2 | Amazon Web Services