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Difficulty: Very hardDesign Compute High Availability

An enterprise is designing the infrastructure for a critical distributed database platform on Azure. The platform consists of two distinct node types: three memory-optimized write nodes (E-series VMs) and three storage-optimized read-replicas (L-series VMs). The architecture must satisfy the following requirements:

* Achieve a compute uptime SLA of 99.99%99.99\% for both the write and read tiers.
* Maintain the lowest possible network latency and highest throughput for replication traffic between the write nodes and read-replicas.
* Allow administrators to perform rolling OS updates, stop, and start individual VMs manually without affecting other instances in the tier.
* Avoid the operational overhead of managing separate availability configurations for each tier.

Which two configurations should you recommend to meet these requirements? (Select two.)

  1. Deploy the virtual machines using a Virtual Machine Scale Set configured with Flexible orchestration mode.Answer
  2. Associate all virtual machines in the scale set with a single Proximity Placement Group.Answer
  3. C
    Deploy the virtual machines in a single Availability Zone using an Availability Set for each VM tier.
  4. D
    Deploy the read-replicas as Spot VMs within the same scale set to optimize cost.

Answer

Deploy the virtual machines using a Virtual Machine Scale Set configured with Flexible orchestration mode, and associate all virtual machines in the scale set with a Proximity Placement Group.
Deploying the virtual machines using a Virtual Machine Scale Set in Flexible orchestration mode allows the system to achieve a 99.99%99.99\% SLA when spread across Availability Zones while supporting heterogeneous VM sizes (E-series and L-series) and individual VM control. Associating the VMs with a Proximity Placement Group ensures that within the zonal boundaries, the physical hosts are co-located as closely as possible to reduce latency and maximize throughput for replication traffic.

Step-by-Step Solution

1
Analyze the SLA requirement of 99.99%99.99\% for the compute tier.
Determine that achieving a 99.99%99.99\% uptime SLA requires deploying VMs across multiple Availability Zones in the same Azure region.
Azure guarantees a 99.99%99.99\% VM uptime SLA only when two or more instances are deployed across two or more Availability Zones.
2
Evaluate VM management requirements, specifically supporting heterogeneous VM sizes and individual VM control.
Identify that Virtual Machine Scale Sets in Flexible orchestration mode are required.
Flexible orchestration allows mixing different VM series (E-series and L-series) in the same scale set and permits individual VM lifecycle operations, unlike Uniform mode or Availability Sets.
3
Evaluate network latency requirements for replication traffic.
Determine that all VMs must be associated with a Proximity Placement Group.
A Proximity Placement Group groups VMs physically close together to achieve the lowest possible network latency.
4
Exclude solutions that fail to meet SLA or introduce eviction risk.
Discard the use of Availability Sets (limited to a 99.95%99.95\% SLA) and Spot VMs (subject to eviction).
Ensures the overall architecture satisfies all availability and reliability goals.

Key Concept

Designing compute high availability in Azure using Virtual Machine Scale Sets in Flexible orchestration mode across Availability Zones combined with Proximity Placement Groups to balance high uptime SLAs with low-latency network performance.
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Design Compute High Availability

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