The fundamental architectural principle is that an application's availability cannot exceed the availability of the underlying infrastructure it runs on, unless the application itself has built-in resiliency mechanisms. The customer has specified a 99.9% availability SLA for the private cloud infrastructure. Therefore, the infrastructure itself cannot guarantee the 99.99% SLA required by the Platinum applications. To bridge this gap, the Platinum applications must be designed with their own high-availability features, such as application-level clustering, database replication, or multi-site load balancing, which allow them to remain available even during an underlying infrastructure component failure. This places the responsibility for achieving the final "nine" of availability on the application layer.

A. This is an artificially restrictive solution that fails to meet the customer's business requirement to host Platinum applications. The architect's role is to find a solution, not to reject the primary requirement.

B. VCF Fleet is a management feature for simplifying the lifecycle management of multiple VCF instances at scale. It does not inherently aggregate multiple instances into a single, higher-SLA infrastructure fabric.

D. Proactive HA is a vSphere feature that improves infrastructure availability by preemptively migrating virtual machines from a host showing signs of impending failure. It contributes to the overall 99.9% infrastructure SLA but does not provide the mechanism to elevate an application's SLA to 99.99%.

1. VMware Cloud Foundation Design Guide (Version 4.5

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Section: Availability): The guide discusses infrastructure availability provided by VCF features like vSphere HA and vSAN. It implicitly supports the concept that application availability is a separate concern. The design of the infrastructure provides a baseline

but "Application-level availability can be provided by clustering services such as Microsoft SQL Server Always On or Oracle Real Application Clusters (RAC)." This directly supports that application-specific features are needed for higher SLAs.

2. VMware vSphere Availability Guide (vSphere 8

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Chapter 2: vSphere HA): This document details the capabilities of vSphere HA

including Proactive HA. It states

"Proactive HA responds to events that occur on a host before a failure results in an outage." While this enhances infrastructure resilience

it is a feature within the infrastructure's availability design and does not guarantee application-specific SLAs that exceed the platform's overall design target.

3. VMware Well-Architected Framework - Reliability Pillar (vmware.com): The framework's principles emphasize designing for failure. It distinguishes between infrastructure reliability and application reliability

stating

"A reliable application is one that can continue to function as expected even when some of its components fail... This can be achieved by designing the application to be resilient to failures

such as by using redundancy and failover mechanisms." This reinforces that application-level design is critical for achieving high availability targets beyond the infrastructure's guarantee.