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Regions, availability zones, and fault domains

A region, is a geographical region on the planet, potentially multiple datacenters in close proximity, networked together. Those datacenters are sometimes called availability zones. An availability zone, has its own independent power and networking. It is set up to be an isolation boundary. If one availability zone goes down, the other continues working. The availability zones are typically connected to each other through very fast, private fiber-optic networks.

Within the availability zone, the VMs are deployed on machines, that are organized in racks. Each rack has its own router. The virtual machines on one single physical machine may run multiple containers.

When an incoming request comes to the endpoint, it is usually first delivered to a load balancer to route the traffic to an instance of a service. The goal is to run the code on different VMs that are not close to each other to reduce the chance of single point of failure. The unit of single point of failure is called a fault domain. With this hierarchy, when:

  • a region goes down, everything inside the region is down.
  • an availability zone goes down, everything inside the availability zone is lost.
  • a rack goes down, it is the PCs that are lost.
  • a PC goes down, it is the VMs on it that are lost.


What are Availability Zones in Azure?

Availability Zones is a high-availability offering that protects your applications and data from datacenter failures. Availability Zones are unique physical locations within an Azure region. Each zone is made up of one or more datacenters equipped with independent power, cooling, and networking. To ensure resiliency, there’s a minimum of three separate zones in all enabled regions. The physical separation of Availability Zones within a region protects applications and data from datacenter failures. Zone-redundant services replicate your applications and data across Availability Zones to protect from single-points-of-failure.

Azure services that support Availability Zones fall into two categories:

  • Zonal services – you pin the resource to a specific zone (for example, virtual machines, managed disks, IP addresses), or
  • Zone-redundant services – platform replicates automatically across zones (for example, zone-redundant storage, SQL Database).

To achieve comprehensive business continuity on Azure, build your application architecture using the combination of Availability Zones with Azure region pairs. You can synchronously replicate your applications and data using Availability Zones within an Azure region for high-availability and asynchronously replicate across Azure regions for disaster recovery protection.



Azure Paired Regions

Each Azure region is paired with another region within the same geography, together making a regional pair. The exception is Brazil South, which is paired with a region outside its geography.

Figure 1 – Azure regional pair diagram


Geography Paired regions
Asia East Asia Southeast Asia
Australia Australia East Australia Southeast
Canada Canada Central Canada East
China China North China East
India Central India South India
Japan Japan East Japan West
Korea Korea Central Korea South
North America North Central US South Central US
North America East US West US
North America East US 2 Central US
North America West US 2 West Central US
Europe North Europe West Europe
Japan Japan East Japan West
Brazil Brazil South (1) South Central US
US Government US Gov Iowa US Gov Virginia
US Government US Gov Arizona US Gov Texas
US Department of Defense US DoD East US DoD Central
UK UK West UK South
Germany Germany Central Germany Northeast

Table 1 – Mapping of Azure regional pairs

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Understand Azure Global Infrastructure

Geographies (Geos)

A geography is a discrete market, typically containing two or more regions, that preserves data residency and compliance boundaries. Geographies allow customers with specific data-residency and compliance needs to keep their data and applications close. Geographies are fault-tolerant to withstand complete region failure through their connection to Microsoft dedicated high-capacity networking infrastructure. Geos examples: US, Europe, Asia Pacific, Japan, Brazil, Australia, China. Learn more  >


A region is a set of datacenters deployed within a latency-defined perimeter and connected through a dedicated regional low-latency network. With more global regions than any other cloud provider, Azure gives customers the flexibility to deploy applications where they need to. Azure is generally available in 40 regions around the world, with plans announced for 10 additional regions

Availability Zones

Availability Zones are physically separate locations within an Azure region. Each Availability Zone is made up of one or more datacenters equipped with independent power, cooling, and networking. Availability Zones allow customers to run mission-critical applications with high availability and low-latency replication.



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Microsoft Azure Cloud Datacenters

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