AZ-800 Administering Windows Server Hybrid Core Infrastructure Exam

Compare and Configure Availability Sets and Zones

In Azure, availability sets group VMs within the same region to improve uptime. They use fault domains and update domains to spread VMs across different hardware and maintenance schedules. This design helps you reduce the chance of correlated failures in a single datacenter rack. By placing at least two VMs in an availability set, you can achieve a 99.95% Azure SLA without extra cost.

In an availability set, resources are split across fault domains and update domains to boost stability. This approach ensures that not all VMs are affected by the same issue. Key domain types include:

• Fault domains: Physical racks with shared power and network. Azure supports up to three fault domains.
• Update domains: Groups of VMs that are rebooted together during maintenance. Azure updates one domain at a time to prevent widespread downtime.
  By managing these domains, Azure maintains service availability during both failures and updates.

In addition to availability sets, Azure offers availability zones for even greater resilience. These zones are geographically separate datacenters within the same region. Each zone has independent power, cooling, and networking to protect against larger outages. Key benefits of availability zones include:

• Top-tier reliability: VMs remain online even if one datacenter fails.
• Enhanced fault isolation: Outages in one zone do not affect others.
  By deploying VMs across multiple zones, you can reach higher SLA levels compared to availability sets.

When you create virtual machines, you choose between availability sets and availability zones based on your needs. Use Azure Portal, Azure CLI, or PowerShell to specify the number of fault domains and update domains for availability sets or to assign zones for availability zone deployments. This configuration helps meet specific SLA and resiliency targets required for business continuity.

Conclusion

Managing uptime in Azure involves understanding the difference between availability sets and availability zones. Availability sets use fault domains and update domains within a single datacenter to prevent correlated failures. Availability zones offer region-spanning redundancy by placing VMs across separate datacenters. Both options help protect workloads but offer different levels of resilience.

By configuring availability sets, you minimize the risk of hardware or maintenance issues affecting all your VMs at once. Using update domains ensures that only a portion of your VMs is rebooted during patches, preventing widespread downtime. On the other hand, deploying across availability zones provides stronger isolation against larger outages. Azure’s design lets you pick the right strategy for your reliability needs.

Choosing the right configuration depends on the required SLA and your tolerance for downtime. For high availability, combining availability sets within zones can deliver even better protection. With Azure CLI or PowerShell, you can automate VM placement and domain assignments to match your business continuity plan. Understanding these concepts is key to building a resilient and reliable cloud infrastructure.