Fundamental
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Fundamental
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Full OS Control for Legacy Apps with IaaS
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An organization plans to migrate an on-premises legacy application to Microsoft Azure. The application requires specific operating system customizations, custom software installations, and complete administrative control over the underlying virtual servers and networking.
Which cloud service model should the organization choose for this migration?
Explanations
Infrastructure as a Service (IaaS)
Infrastructure as a Service (IaaS)
What Infrastructure as a Service (IaaS) Is
Infrastructure as a Service (IaaS) is a foundational cloud computing model that provides on-demand access to fundamental computing resources, including virtual machines (VMs), storage disks, and virtual networking infrastructure. Under IaaS, the cloud provider manages the physical data centers, host hardware, and physical virtualization layers, while the customer retains full management control over the guest operating system, middleware, runtime environments, and installed software.
How It Meets the Organization's Requirements
- Operating System Control: IaaS allows administrators to select, configure, and maintain the guest operating system, providing the administrative access needed for custom OS-level tweaks.
- Legacy Application Support: Applications with legacy components or dependencies that cannot run in modern managed application runtimes can be lifted and shifted directly onto Azure virtual machines.
- Custom Software Dependencies: Organizations can install specialized third-party software, utilities, or background services directly onto the server without platform restrictions.
Key Advantages and Capabilities
- Maximum Configuration Flexibility: Acts like a "box of parts," enabling teams to assemble, configure, and fine-tune computing resources to exact workload specifications.
- Direct Administrative Access: Provides full administrator/root permissions via protocols such as RDP or SSH for deep OS-level troubleshooting and configuration.
- Rapid Lift-and-Shift Migrations: Minimizes the need to refactor or rewrite application code during on-premises cloud migrations.
- Custom Networking & Storage: Enables granular setup of virtual networks, subnets, firewalls, routing tables, and attached disk volumes.
Why This Is Optimal
Because the organization's legacy application requires specific operating system configurations and complete administrative access, IaaS is the only model that delivers the necessary control over the virtual server environment without forcing architectural code rewrites.
Platform as a Service (PaaS)
Platform as a Service (PaaS)
What Platform as a Service (PaaS) Is
Platform as a Service (PaaS) is a cloud computing tier that provides an environment for developers and organizations to build, deploy, and manage applications without the burden of provisioning or managing the underlying servers, operating systems, storage, and network components.
Why It Doesn't Meet the Requirement
While PaaS reduces administrative overhead by handling routine maintenance, OS updates, and automatic patching, it abstracts away underlying server access. Users typically do not have direct administrator or root access to the operating system, making it unsuitable for legacy applications requiring custom OS-level configurations, deep registry modifications, or non-standard server software.
Key Characteristics and Limitations
- No Direct OS Management: Users cannot configure the underlying operating system or install arbitrary background daemon services.
- Managed Infrastructure: The cloud provider handles patching, security updates, and operating system lifecycle management automatically.
- Runtime Constraints: Workloads are restricted to supported programming languages, frameworks, and managed execution runtimes.
- Simplified Scaling: Native features support automated scale-up and scale-out rules without managing individual virtual machines.
This Answer Would Be Correct If
The organization were developing new web applications or microservices and wanted developers to focus purely on business logic and application code without maintaining virtual machines, operating system patches, or server infrastructure.
Software as a Service (SaaS)
Software as a Service (SaaS)
What Software as a Service (SaaS) Is
Software as a Service (SaaS) is a cloud delivery model where end-user software applications are entirely hosted, operated, and maintained by a cloud vendor. Users access the applications over the internet, typically via a web browser or lightweight desktop/mobile client, using a subscription-based pricing model.
Why It Doesn't Meet the Requirement
SaaS provides a ready-to-use end-user product rather than a hosting infrastructure for custom or legacy in-house applications. In a SaaS model, the customer has zero access to the underlying hardware, networking, operating system, or application runtime, meaning an existing custom enterprise application cannot be deployed or hosted within a SaaS offering.
Key Characteristics and Limitations
- End-User Focused: Designed for immediate end-user consumption rather than developer deployment or custom application hosting.
- Zero Infrastructure Control: Customers cannot install custom software, access virtual machine environments, or configure server operating systems.
- Provider-Managed Stack: The vendor assumes complete responsibility for application code, updates, data backups, and underlying infrastructure.
- Configuration Over Customization: Customization is limited strictly to user interface settings, user profiles, and built-in tenant configurations.
This Answer Would Be Correct If
The organization wanted to replace an entire business function (such as corporate email, CRM, or office productivity suites) with a fully managed turnkey solution like Microsoft 365 or Microsoft Dynamics 365.
Serverless Computing
Serverless Computing
What Serverless Computing Is
Serverless Computing (often associated with Functions as a Service or FaaS) is an execution model where cloud resources are dynamically allocated and billed based strictly on event execution. The cloud service automatically executes snippets of code in response to events or triggers (such as HTTP requests, database events, or message queues) and scales instantly down to zero when idle.
Why It Doesn't Meet the Requirement
Serverless platforms completely abstract server infrastructure and are stateless, ephemeral, and event-driven by design. They cannot host persistent legacy monoliths or applications requiring long-running operating system processes, specialized server installations, custom OS drivers, or sustained administrative server access.
Key Characteristics and Limitations
- Event-Driven Execution: Code executes only in response to specific system triggers and events.
- Ephemeral and Stateless: Instances are spun up and torn down dynamically without persistent local machine state.
- Execution Time Limits: Function invocations often enforce hard execution time limits and cannot run persistent server daemons.
- No Infrastructure Visibility: Developers have zero visibility or control over operating systems, machine patching, or low-level virtual networking.
This Answer Would Be Correct If
The organization needed to run short, event-triggered background tasks, process incoming IoT telemetry, or execute stateless microservices on demand without provisioning ongoing server resources.
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