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Difficulty: MediumConfigure VMs for High Availability

An organization, Titan Sports, is planning the deployment of a new multi-tier application in the Australia East region. The application consists of four virtual machines: VM-Web1, VM-Web2, VM-App1, and VM-App2. The deployment must guarantee a 99.99%99.99\% uptime SLA at the virtual machine level and protect the application against datacenter-wide failures. Which configuration should you implement?

  1. Deploy VM-Web1 and VM-App1 in Availability Zone 1, and deploy VM-Web2 and VM-App2 in Availability Zone 2.Answer
  2. B
    Deploy all four virtual machines within a single Availability Set in the Australia East region.
  3. C
    Deploy VM-Web1 and VM-Web2 in Availability Zone 1, and deploy VM-App1 and VM-App2 in Availability Zone 2.
  4. D
    Deploy all four virtual machines in a single Availability Set that spans across two Availability Zones.

Answer

Deploy VM-Web1 and VM-App1 in Availability Zone 1, and deploy VM-Web2 and VM-App2 in Availability Zone 2.
Deploying the web and application tier virtual machines across multiple Availability Zones ensures protection against datacenter-wide failures and provides a 99.99%99.99\% VM uptime SLA. By placing VM-Web1 and VM-App1 in Zone 1, and VM-Web2 and VM-App2 in Zone 2, a failure in either zone leaves at least one active web server and one active application server running in the other zone.

Step-by-Step Solution

1
Analyze the SLA and high availability requirements.
The application requires a 99.99%99.99\% virtual machine uptime SLA and protection against datacenter-wide failures.
An SLA of 99.99%99.99\% for virtual machines in Azure requires deploying two or more instances across different Availability Zones. Availability Sets only offer a 99.95%99.95\% SLA and do not protect against datacenter-wide outages.
2
Design the distribution of virtual machines across the tiers.
Each tier (Web and App) must have at least one virtual machine running in each zone.
If an entire tier is placed in a single zone, a zone failure will make that entire tier unavailable, rendering the application offline despite having other tiers running.
3
Map the VMs to the target Availability Zones.
VM-Web1 and VM-App1 go to Zone 1; VM-Web2 and VM-App2 go to Zone 2.
This cross-zone distribution maintains the availability of both tiers if either zone fails.

Key Concept

To achieve a 99.99%99.99\% SLA and protect against datacenter-wide failures, virtual machines must be deployed across multiple Availability Zones. Workloads must be distributed such that each application tier has active instances in each zone.
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Topics

Configure VMs for High Availability

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