An organization plans to migrate a legacy on-premises application to Microsoft Azure without modifying the application code. The IT team requires complete control over the operating system, disk storage, and virtual network configuration to replicate their existing environment. Which cloud service model should the organization use for this migration?

Infrastructure as a Service (IaaS): ### What Infrastructure as a Service (IaaS) Is **Infrastructure as a Service (IaaS)** is a cloud computing category where a cloud vendor provides fundamental compute, network, and storage resources on demand over the internet. In an IaaS model, the cloud provider manages the physical hardware, data centers, virtualization layer, and physical networking, while the consumer retains direct administrative control over the operating system, middleware, storage disks, installed runtimes, and networking configurations. ### How It Meets the Scenario Requirements - **OS and Application Control**: **Azure Virtual Machines** provide administrators with complete root or administrative access to customize the guest operating system and install legacy software dependencies. - **Lift-and-Shift Support**: IaaS allows workloads to be migrated directly from physical servers or on-premises hypervisors into the cloud without refactoring application code. - **Custom Storage and Networking**: Organizations can allocate specific virtual hard disks (VHDs), configure **Azure Virtual Networks**, establish custom subnets, and assign private IP addresses to mirror on-premises topologies. ### Key Advantages and Capabilities - **Maximum Flexibility**: Offers total freedom to configure OS patches, security baselines, and background system services. - **Rapid Cloud Onboarding**: Minimizes application refactoring and development overhead during lift-and-shift cloud migrations. - **Granular Resource Sizing**: Allows teams to resize virtual machine SKUs and disk performance tiers as performance demands change. - **Cost Efficiency**: Operates on a pay-as-you-go consumption model, billing only for compute seconds and allocated storage used. ### Why This Is Optimal Because the organization specifically requires full administrative control over the underlying operating system and must migrate legacy software without code refactoring, **IaaS** is the only service model that provides the necessary hardware abstraction while maintaining OS-level authority.