AZURE PHYSICAL INFRASTRUCTURE

The core architectural components of Azure may be down into Two main groups namely...
(!) The Physical Infrastructure
(2) The Management Infrastructure
but the deliberation is on Physical Infrastructure.
The physical infrastructure for Azure starts with Datacenters. Datacenters are facilities with resources arranged in racks with dedicated power, cooling and network infrastructure.
As a global cloud provider, Azure has data centers around the world.
However individual datacenters are not directly accessible, thereby giving rise to grouping of datacenters into Azure regions or Azure availability zone, designed to help users achieve resiliency and reliability for business critical workloads.

(A)Azure Regions: is a geographical area on the planet that contains at least one datacenter, but potentially multiple datacenters that are nearby and networked together in a low latency network. Azure intelligently assigns and controls the resources within each region to ensure workloads are appropriately balanced. When deploying resources in Azure, you will need to choose the region you want the resources deployed.
NOTE: some services or Virtual Machine (VM) features are only available in certain regions, such as specific VM sizes or storage types. some global Azure services don't require selection of particular region, such as Azure Active Directory (AAD), Azure Traffic Manager(ATM) and Azure DNS.

(B)Azure Availability Zones: are physically separated datacenters within an Azure region. Each availability zone is made up of one or more datacenters equipped with independent Power, Cooling and Networking. Availability zone is set up in such a way that if one zone goes down, the other continues working, they are connected through high-speed private fiber optic network.

Availability zones are primarily for VMs, managed disk, load balancers and SQL databases. Azure services that that supports availability zones are divided into three categories :

(1)Zonal Service: you pin the resources to a specific zone (eg ,VMs managed disks IP addresses)

(2)Zone redundant services: this platform replicate automatically across zones(eg zone redundant storage SQL databases)

(3)Non regional services: are resilient zone wide outages as well as region wide outrages.

REGIONAL PAIRS:
most Azure regions are paired with another region within the same geography(such as US, Europe or Asia) at least 300 miles away. This approach allows for the replication of resources across a geography that helps reduce the likelihood of interruptions because events such as natural disasters, civil unrest, power outages, or physical network outages that affects an entire region. For example a region in a pair was affected by a natural disaster, service would automatically fall over to the other region in it's region pair.

NOTE: not all Azure services automatically replicate data or automatically fall back from a failed region to cross replicate to another enabled region, in these scenarios, recovery and replication must be configured by the customer.

Advantages of Regional Pairs
1-If an extensive Azure outage occurs, one region out of every pair is prioritized to make sure at least one is restored quickly.

2-Plan Azure updates are rolled out to paired regions one at a time to minimize down-time and risk of application outage.

3-Data continues to reside within the the the same geography as it's pair(except for Brazil South) for tax and law-enforcement jurisdiction purpose.

NOTE; Most directions are paired in two directions, meaning they are the region that backs up for them e.g (West US and East US back each other up)

SOVEREIGN REGIONS; In addition to regular regions, AZURE also has sovereign regions . This regions are instances of Azure that are isolated from the main instance of Azure.
You might need to use a sovereign region for compliance or legal purposes.
Following are Sovereign regions;
(a)US DoD Central, US Gov Virginia, US Gov Iowa and more. These regions are physically and logically network-isolated instances of Azure for US government agencies and partners. The Datacenters are operated by screened US personnel and include additional compliance certifications.
(b)China East, China North, and more. these regions are available through a unique partnership between Microsoft and 21Vianet whereby Microsoft doesn't directly maintain the Datacenters.