Fundamental
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Fundamental
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IaaS Administrative Control of Guest Operating Systems
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An enterprise is planning to migrate several legacy on-premises applications to Azure. The operations team requires full administrative access to configure the underlying operating systems, run custom background services, and manage OS-level patching directly using Azure Update Manager.
Which cloud service model should the enterprise select to fulfill these management requirements?
Explanations
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 the service provider hosts, manages, and delivers a complete, end-user software application over the internet. Users access the software typically via a web browser, mobile app, or thin client, while all underlying infrastructure, code, runtimes, and operating systems are entirely maintained by the vendor.
Why It Doesn't Meet the Requirement
- End-User Application Focus: SaaS delivers turnkey software rather than raw compute or hosting environments for custom legacy applications.
- Zero Infrastructure Control: Customers have no visibility or control over operating systems, compute sizing, or underlying software configurations.
- Vendor-Managed Lifecycle: Patching, updates, features, and security fixes are rolled out automatically by the software provider without customer intervention.
Key Characteristics and Limitations
- Subscription-Based Consumption: Typically billed on a per-user, per-month, or usage-tier model.
- Minimal Customer Management: Customers are only responsible for configuring user access, basic data settings, and organizational permissions.
- Pre-Built Functionality: Designed for general productivity, analytics, or enterprise management (such as Microsoft 365 or SaaS-based analytics platforms).
This Answer Would Be Correct If
The organization wanted to consume an existing ready-to-use application (such as email, CRM, or a managed analytics tool) without hosting or managing any code or servers.
Additional Context
SaaS represents the highest level of provider responsibility in the shared responsibility model, offering the least amount of technical control to the customer.
Serverless Computing / Function as a Service (FaaS)
Serverless Computing / Function as a Service (FaaS)
What Serverless Computing Is
Serverless Computing (often implemented as Function as a Service or serverless runtime environments) is an execution model where cloud resources are dynamically allocated and executed only in response to specific events, triggers, or requests. The cloud platform handles all scaling, runtime provisioning, and machine management automatically behind the scenes.
Why It Doesn't Meet the Requirement
- No Persistent Server Access: Serverless environments execute ephemeral tasks or individual functions without granting access to a persistent operating system.
- Abstracted Execution: The user does not interact with the host OS, making it impossible to install legacy system services or utilize custom OS management tools.
- Event-Driven Architecture: Designed for short-lived, event-triggered compute tasks rather than traditional long-running legacy servers.
Key Characteristics and Limitations
- Automatic Scaling: Scales instantly from zero to thousands of instances based on incoming request volume.
- Consumption-Based Pricing: Costs are incurred strictly for the compute units and duration consumed while the code is actively executing.
- Stateless Design: Requires workloads to be modular, stateless, and capable of terminating cleanly after execution.
This Answer Would Be Correct If
The organization needed to run event-triggered backend tasks, data integration pipelines, or lightweight code snippets without provisioning any dedicated virtual infrastructure.
Additional Context
Serverless is an extension of the PaaS paradigm that completely abstracts servers, contrasting directly with the infrastructure-level control offered by IaaS.
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 delivery model that provides a managed application development and deployment framework. Under PaaS, the cloud provider manages the physical infrastructure, virtualization, operating systems, runtime engines, and database systems, allowing developers to focus solely on writing and deploying application code and configuring application data.
Why It Doesn't Meet the Requirement
- No Direct OS Management: PaaS abstracts the underlying operating system, meaning users do not receive administrative access to configure or patch the OS.
- Limited Customization: Legacy software requiring specific operating system dependencies, registry modifications, or custom background daemons cannot run on standard PaaS offerings.
- Automated Maintenance: Operating system updates and security patches are managed automatically by the cloud provider rather than controlled via user tools like Azure Update Manager.
Key Characteristics and Limitations
- Development Focus: Optimized for building and hosting web apps, APIs, and microservices rapidly.
- Shared Management: The cloud provider is strictly responsible for OS maintenance, runtime patching, and hardware capacity.
- Reduced Operational Overhead: Eliminates server maintenance tasks, which conflicts with the requirement for manual OS control.
This Answer Would Be Correct If
The organization wanted to build or deploy web applications without worrying about server provisioning, OS configuration, or patching schedules.
Additional Context
PaaS sits between IaaS and SaaS in the shared responsibility model. While it increases developer productivity, it restricts low-level administrative control.
Infrastructure as a Service (IaaS)
Infrastructure as a Service (IaaS)
What Infrastructure as a Service (IaaS) Is
Infrastructure as a Service (IaaS) is a cloud computing service model where a cloud vendor provides users with access to fundamental computing resources such as virtual machines (VMs), storage, and networking over the internet. In an IaaS model, the cloud provider maintains the physical hardware, data center facilities, and virtualization layer, while the customer retains control and administrative management over the guest operating systems, middleware, runtime environments, and installed applications.
How It Meets the Enterprise Requirements
- Operating System Control: IaaS grants full administrative privileges (such as root or administrator access) over the virtual machine instances, allowing teams to configure low-level OS settings and kernel parameters.
- Custom Software Support: Organizations can install legacy applications, custom drivers, and background services that require specific OS versions or configurations.
- Patching and Maintenance: Operations teams retain full responsibility for scheduling and executing updates across their fleet of Windows and Linux machines using services like Azure Update Manager.
Key Advantages and Capabilities
- Maximum Flexibility: Allows complete customization of server environments without physical hardware constraints.
- Familiar Architecture: Serves as the primary model for "lift-and-shift" migrations from on-premises data centers.
- Fine-Grained Governance: Supports integration with tools such as Azure Resource Manager (ARM) templates, Bicep, and VM extensions for repeatable infrastructure as code.
- Direct Resource Allocation: Enables exact specification of compute sizing, disk types, and network topologies.
Why This Is Optimal
Compared to higher-level cloud abstractions, IaaS is the only model that gives the organization total ownership of the operating system and installed software stack. It provides the precise balance of cloud scalability while satisfying administrative and legacy compatibility constraints.
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