Azure VM High Availability ? (Part-3 : Availability Zone)

Aammir Mirza
3 min readSep 15, 2023

What is Availability Zone?

Availability Zones in Azure enhance the availability discussed earlier, but within a single region across multiple data centers. These data centers can be grouped within a zone or span multiple zones, all under the umbrella of a single region. However, if all data centers within a zone are down, availability is lost. Each Availability Zone consists of multiple data centers, and you must plan replication across data centers and availability zones within the same region.

Implementing Availability Zones drastically reduces system downtime to less than 5 minutes per month, backed by a robust 99.99% VM uptime SLA. This setup introduces Zone Aware services, distributing workloads across diverse zones within an Azure region. Each zone is composed of one or more data centers, each with independent power, networking, and cooling infrastructure. Low-latency links interconnect Availability Zones within a region, ensuring high availability and fault tolerance.

Note that not every Azure region has Availability Zones.

Here are the 3 key benefits of using Availability Zones:

  • Low Latency
  • High Availability
  • Global Deployment

In other words, Azure Availability Zones represent a high-availability offering that protects your applications as well as data against datacenter failures. They are distinct physical locations in an Azure region. They can be deployed with the help of single or multiple VMs in an Azure region. Moreover, zone-redundant services duplicate your applications as well as data throughout the Azure Zones. The motive behind this is to protect them against single-points-of-failure.

Two categories of Availability Zones:

  • Zonal Services: They add the resource to a particular zone. Examples include VMs, IP addresses, and managed disks.
  • Zone-redundant services: They work on automatic replication across zones. They are enabled for zone-redundant storage and SQL Database.

How to configure an Availability Zone?

It is quite simple to configure an Availability Zone from the Azure Portal. You just have to choose the number of the Zones that the VMs would use.

You need to make this selection from the Availability Zone drop-down. It is possible to simultaneously deploy your managed disk and your public IP (if you have one).

Note: To benefit from a 99.99% SLA, you should deploy a minimum of two VMs in at least two diverse zones.

Availability Set vs. Availability Zone: Differences:

Availability Set Availability Zone

SLA 99.95 % SLA 99.99%

Protects against hardware failures in data centers Protects against whole data center failure.

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Aammir Mirza

Cloud Architect with 12 years of experience in managing cloud infrastructure and automation, integrating Azure cloud-based infra components