Azure Availability Zones

Azure Availability Zones

An Availability Zone can also be abbreviated as AZ and represents a physical location that is made up of one or more data centers. A data center is a highly secure building that has hundreds of thousands of computers all working together to offer the cloud services that Azure makes available to businesses worldwide. An Availability Zone is contained within a Region and has independent power, network, and cooling. They are a core concept of Microsoft Azure and something that every cloud engineer should be familiar with.


Regions Contain Availability Zones

As mentioned above, Availability Zones exist in an Azure Region. A general rule of thumb is that an Azure Region contains 3 Availability Zones, though there are exceptions. Availability Zones contained within a Region are isolated from each other, meaning they are in different physical buildings. The AZs will be close enough however such that latency between buildings is very low and minimized.

Workloads In 3 Availability Zones

A common technique used is to run production workloads in at least 3 Availability Zones. This is done to make sure services are available at all times in the case of a data center failure. This is also known as High Availability.

Region And Availability Zone

azure availability zones in a region

In the diagram above is a representation of the US East 1 Region and the three Availability Zones contained within it: AZ1, AZ2, and AZ3. When launching services in the Azure Portal, you first choose your region, and then if you specify to use an Availability Zone, you choose which Zone to launch the service into, 1, 2, or 3. In the diagram here, AZ2 is chosen so that is where the service will be deployed to.

AZ Bullet Points

availability zone within region

Azure High Availability Options

Azure high availability includes many options, allowing increasingly more certainty that an application will continue to run in the event of a failure. The list below displays 4 options for ensuring a Virtual Machine is highly available. The architecture of Azure Availability Zones can extend beyond VMs to additional Azure services.

  • Single VM: This is when you run a Virtual Machine (VM) on Azure with no replication.
  • Availability Sets: When a Virtual Machine with one or more replicated copies on separate hardware within the same Availability Zone is configured.
  • Availability Zones: A Virtual Machine with one or more replicated copies on different Availability Zones, providing resiliency against data center failure.
  • Region Pairs: A VM with one or more replicated copies on different Azure Regions (but always staying within the same geopolitical boundary, usually meaning the same country), protecting against widespread outages.

Availability Zones Supported Regions

As we saw earlier, there are two types of Regions in Azure that do not have Availability Zones:

  • Alternate
  • Other

What does have Availability Zones are the Recommended Regions. Recommended Regions are supposed to have 3 Availability Zones. If it does not have all 3 AZs available, it just means that the recommended region in question is too new. As a rule of thumb, you want to launch highly available cloud services in a region that does have all 3 Availability Zones. As of this writing, the following Regions have a least three Availability Zones.

Supported Regions Table

Americas Europe Africa Asia Pacific
Brazil South France Central South Africa North Australia East
Canada Central Germany West Central Central India
Central US North Europe Japan East
East US Norway East Korea Central
East US 2 UK South Southeast Asia
South Central US West Europe
US Gov Virginia
West US 2
West US 3

Cases Of No Availability Zones

When launching a cloud service in Azure that uses a Region with no Availability Zones such as Brazil South, you will need to choose the option of No infrastructure redundancy required.

azure No infrastructure redundancy required

Supported Services and Resources In Microsoft Azure

  • Azure Virtual Machines – Virtual machines are the prime example of a service that can be configured for replication with Availability Zones. This is configured during the Virtual Machine creation process. Recall that a service must be configured in an Availability Zone to guarantee redundancy.
  • VM Scale Set – Virtual Machine Scale Sets makes it possible to create and manage a group of identical, load-balanced VMs, and dynamically add or remove VMs from the set. Make use of Availability Sets to deploy a single set per Availability Zone, and load balance traffic across zones.
  • Azure SQL Database – Zone Redundant Configuration is a popular approach for SQL Database Service in Azure. Note that only the Premium or Business Critical tiers have this offering.
  • Azure Standard Load Balancer – The Azure Load Balancer Service has support for Availability Zones. It can be used to direct traffic within a zone or across multiple Availability Zones. The latter is what is known as Zone Redundancy.

Availability Zone Summary

  • Azure Availability Zones is a high-availability service that protects applications and data from datacenter failures.
  • These are unique physical locations within an Azure region. Each zone is made up of one or more data centers equipped with its own powercooling, and networking.
  • The physical isolation of Availability Zones within a region protects applications and data from datacenter failures.
  • Zone-redundant offerings replicate applications and data across Azure Zones to protect from single-points-of-failure.
  • Not every region has support for Availability Zones.
  • Availability Zones offer industry best 99.99 percent VM uptime Service Level Agreement
  • Protects against datacenter-level failures