Microsoft Azure is generally available in over 60+ regions around the world. Each Azure Region is home to a vast array of services hosted within multiple datacenters in the region. Separate regions is very apparent within Microsoft Azure, as you need to choose a specific Azure Region to host your services within. Although, something that’s not very apparent is the concept of Azure Region Pairs. Specific Azure regions are paired together for disaster recovery purposes. This article discusses what Azure Region Pairs are, and the benefits that come with having them be a part of the Microsoft Azure cloud platform.

What are Azure Region Pairs?

An Azure Region Pair is a relationship between 2 Azure Regions within the same geographic region for disaster recovery purposes. If one of the regions were to experience a disaster or failure, then the services in that region will automatically failover to that regions secondary region in the pair. For example, North Central US region’s pair is South Central US.

Almost all the Azure Regions are located within the same geographic region as at least 1 other Azure Region; it’s Region Pair. The only exception to this rule is the Brazil South region, which is the only Azure Region in Brazil, so it’s Region Pair is South Central US in a one-way pairing connection, as South Central US’s pair is North Central US. I know this sounds confusing, but this is the only Azure Region who’s pair is outside it’s geographic region.

The Azure Region Pairs are more than just a visual concept to think about with Azure Regions. The Azure Region pairs are connected directly together and offer multiple benefits when utilized together in the same distributed or redundant system. Before we get into these benefits of Azure Region Pairs, let’s first discuss the Azure Regions and Datacenters in further details.

Azure Regions in a Pair have direct connections which bring additional benefits to use them together.

The geographic disparity of Azure Regions is important. Global distribution of Azure Regions is strategic according to geography. There are many factors involved in their placement; from geo-political to internet latency for large population centers. However, Azure Region pairs have another big consideration that defines where they are placed.

Each Azure Region in a pair are always located greater than 300 miles apart when possible. This is to isolate each region in the pair from being affected by the same regional disasters that could take one of the regions down. These disasters could be earthquakes, hurricanes, tornados, fires, or some other natural or man-made disaster.

Each Azure Region in a pair are always located greater than 300 miles apart when possible.

Since each Azure Region in an Azure Region Pair are directly connected to each other and the are far enough apart to be isolated from regional disasters, it is recommended by Microsoft that when replicating data or interacting with services across regions that you use Region Pairs.

While you could use more geographically dispersed Azure Regions for replication, redundancy, and more, there are a number of benefits Azure Region Pairs provide. Next, let’s discuss the benefits of Azure Region Pairs.

What are the Azure Region pairs?

Before we get into the benefits of Azure Region Pairs, let’s cover what Azure Regions are paired. Here is a list of a few of the Microsoft Azure Region Pairs:

Her’s a couple notes about the region pairs listed in the table:

• West India is paired to South India in one direction only. South India’s region pair is Central India.
• Brazil South is paired (in one direction) with the South Central US region outside its geographic region. This is a unique region, as it’s the only one without a pair in the same geographic region.
• The US Government regions have similarly unusual paring. The US Gov Iowa’s secondary region is US Gov Virginia; US Gov Virginia’s secondary region is US Gov Texas; and US Gov Texas’ secondary region is US Gov Arizona

When setting up services like SQL Database Geo-Replication and other services, the Azure Portal will guide you by telling you the “recommended” Azure Region to use as a secondary. This will always be the Azure Region Pair, so you don’t need to memorize the entire list Azure Region Pairs.

What are the benefits to Azure Region Pairs?

Some of the benefits to Azure Region Pairs were already discussed. There are a number of benefits to utilizing Azure Region Pairs that add to the basic benefit of geographic isolation. Let’s dig in to a few more of the benefits.

How is Data Residency handled?

The location of data stored within a geography can be very important. There are geo-political, tax, law enforcement jurisdiction, compliance, or other reason that an enterprise may require all their data to be located within the bounds of a certain country. This is the main reason why both regions in Azure Region Pairs are located within the same geographic region; most often within the same country.

How does Microsoft Azure manage System Update Isolation when pushing out updates to the Azure Regions?

Microsoft maintains a huge amount of software and infrastructure that runs and automates the Azure datacenters. When rolling out updates to this “backbone” system, Microsoft will update a single region in the pair first. Then they will validate the update before moving on to the next region in the pair. This sequential updating of the Azure Regions in a pair ensures minimal downtime in the event of bugs or logical failures caused by an update. By using Azure Region Pairs for replication and redundancy will ensure your applications and services are not adversely affected by a rare bad update event.

What about the Region Recovery Order in the event of a disaster?

In the event of a massive Azure outage, each Azure Region Pair has a single region that is prioritized over the other for recovery. Systems deployed across multiple Azure Regions within a pair are guaranteed to have an Azure Region that will be recovered with high priority.

What about the Platform-provided Replication between regions?

There are some services within Microsoft Azure that provide automatic geo-redundant storage. These services will do this by utilizing the paired region automatically.

For example, when you provision an Azure Storage account and configure it for geo-replication then it will automatically use the region the Storage Account is provisioned in as the primary with replication to that regions secondary paired region without any additional configuration.

What about the Physical Isolation between Azure Regions?

Each Azure Region within a pair is physically / geographically located at least 300 miles apart where possible. This helps isolate the pair so that a regional disaster (earthquake, hurricane, fire, riot, power outage, etc.) affects only a single region within the pair.

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