Microsoft is not very secretive about its infrastructure, but finding public information and stitching it together is not always straightforward. For now, here are a bunch of links to helpful information.
Physical infrastructure
Microsoft both leases and owns the datacenters in which Azure is deployed.1
Azure Networking
Azure’s frontend network is documented here: Azure network architecture
Security
The physical security of Azure datacenters is documented here: Physical security of Azure datacenters
Logical infrastructure
Azure uses a Windows-based hypervisor.
Security
The security features of the Azure platform are documented here: Azure platform integrity and security. There are subpages that document:
- Host attestation
- Where encryption is implemented
Multitenancy
Related to security, Azure’s protections in multitenant environments (e.g., Coke and Pepsi both using the same physical server or storage cluster) are documented here: Isolation in the Azure Public Cloud