Fundamental
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Fundamental
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Infrastructure as a Service With Full OS Control
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An organization is migrating an existing on-premises legacy application to Azure with minimal architectural changes. The internal IT team requires full administrative control over the guest operating system, custom middleware configurations, and underlying virtual network settings, while offloading physical hardware maintenance and facility management to Microsoft.
Which cloud service model best aligns with the organization's requirements?
Explanations
Function as a Service (FaaS)
Function as a Service (FaaS)
What Function as a Service (FaaS) Is
Function as a Service (FaaS), commonly known as serverless computing, allows developers to execute discrete blocks of code or event-driven micro-tasks in response to triggers without managing any long-running servers or application hosting environments. Services like Azure Functions represent this model.
Why It Doesn't Meet the Requirement
- Stateless and Short-Lived: FaaS is designed for brief, stateless event handling and cannot sustain a traditional full-featured legacy application.
- Total Server Abstraction: Operating systems and execution environments are completely abstracted, offering zero administrative control over host configuration.
- Architectural Incompatibility: Legacy N-tier applications cannot run inside serverless functions without being completely rewritten into microservices.
Key Characteristics
- Event-Driven Execution: Runs code only when invoked by HTTP requests, timers, or message queue events.
- Dynamic Auto-Scaling: Scales instantly from zero to thousands of concurrent executions based on event traffic.
- Micro-Billing: Customers pay only for the exact compute resources consumed during function execution.
This Answer Would Be Correct If
The organization needed to run event-triggered automation scripts or microservices without maintaining any permanent server infrastructure.
Platform as a Service (PaaS)
Platform as a Service (PaaS)
What Platform as a Service (PaaS) Is
Platform as a Service (PaaS) delivers a fully managed cloud environment designed for building, testing, deploying, and managing modern applications. In a PaaS deployment, the cloud vendor manages the underlying infrastructure, operating systems, hardware provisioning, runtime environments, and middleware, allowing developers to focus solely on application code and data.
Why It Doesn't Meet the Requirement
- No Operating System Access: PaaS abstracts away the underlying operating system, preventing administrators from accessing root OS settings or managing server-level patches.
- Incompatible with Legacy Dependencies: Legacy applications often depend on custom OS-level components, specific registry keys, or custom background services that cannot run in a managed PaaS runtime.
- Requires Code Refactoring: Migrating traditional monolithic or N-tier workloads to PaaS often necessitates architectural changes rather than a minimal-change lift-and-shift approach.
Key Characteristics
- Managed Infrastructure: Automatic OS patching, security updates, and automated scaling.
- Developer Focus: High productivity by removing operational burdens related to server management.
- Integrated Services: Built-in features such as deployment slots, automated backups, and integrated developer tools.
This Answer Would Be Correct If
The organization wanted to build cloud-native applications or deploy web apps where developers manage only source code and database schemas without needing any access to the host operating system.
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 where a cloud provider provisions and manages basic computing infrastructure, including physical servers, storage systems, networking hardware, and datacenter facilities. The customer rents these resources and retains full control over the operating systems, runtime environments, middleware, and deployed applications.
How It Meets the Requirements
- Full OS and Configuration Control: IaaS provides virtual machines (VMs) where administrators have root or administrator-level access to install custom middleware, modify registry settings, and manage patches.
- Minimal Code Modification: Because IaaS closely mimics traditional physical server environments, existing on-premises applications can be migrated through a lift-and-shift approach with little to no refactoring.
- Reduced Physical Overhead: The cloud provider takes ownership of hardware procurement, server lifecycle maintenance, physical datacenter security, and power management.
Key Advantages
- Maximum Flexibility: Allows complete customization of server operating systems and networking topologies.
- Smooth Cloud Migration: Serves as the most straightforward path for transitioning legacy workloads from on-premises datacenters.
- Pay-As-You-Go Cost Efficiency: Eliminates upfront capital expenditure (CapEx) for physical hardware in favor of operational expenditure (OpEx).
- Hybrid Cloud Compatibility: Facilitates seamless network connectivity between on-premises environments and cloud-hosted virtual networks.
Why This Is Optimal
Compared to PaaS and SaaS models, IaaS provides the exact level of granular administrative control needed for legacy systems requiring specific OS builds, without forcing the organization to redesign application architectures.
Software as a Service (SaaS)
Software as a Service (SaaS)
What Software as a Service (SaaS) Is
Software as a Service (SaaS) is a complete software application delivery model where end users access centrally hosted, fully functioning applications over the internet on a subscription basis. Well-known examples include Microsoft 365, Dynamics 365, and cloud email services.
Why It Doesn't Meet the Requirement
- Zero Infrastructure and Platform Control: SaaS leaves all infrastructure, operating systems, networking, runtimes, and application code in the hands of the software vendor.
- Cannot Host Custom Legacy Apps: SaaS provides a ready-made commercial application rather than an environment where an enterprise can host and execute custom legacy software.
- Configuration Restricted to Application Settings: End users and administrators can only modify end-user settings and permissions within the boundary of the vendor's application.
Key Characteristics
- Turnkey Solutions: Users consume finished products directly via web browsers or client applications.
- Lowest Management Overhead: The service provider handles all hardware, software maintenance, upgrades, and security fixes.
- Subscription-Based Licensing: Typically billed per user per month or by consumption tiers.
This Answer Would Be Correct If
The organization intended to replace an internal software tool entirely with a turnkey, vendor-managed business solution such as an email platform or CRM system.
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