Azure Availability Zones
- Roger Cruz
Intro
My notes on availability zones
Documentation
Tips and Tidbits
An Availability zone is a physically separate zone, within an Azure region.
There are three Availability Zones per supported Azure region.
Each Availability Zone has a distinct power source, network, and cooling.
If one zone is compromised, then replicated apps and data are instantly available in another zone.
The Availability Zone identifiers (the numbers 1, 2 and 3 in the picture above) are logically mapped to the actual physical zones for each subscription independently. That means that Availability Zone 1 in a given subscription might refer to a different physical zone than Availability Zone 1 in a different subscription. As a consequence, it's recommended to not rely on Availability Zone IDs across different subscriptions for virtual machine placement.
The Azure platform recognizes app distribution across zones (ie update domains) to make sure that VMs in different zones are not scheduled to be updated at the same time.
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.
Availability zone requires managed disks.
For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time
SLA For Virtual Machines
For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time.
For all Virtual Machines that have two or more instances deployed in the same Availability Set or in the same Dedicated Host Group, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.95% of the time.
For any Single Instance Virtual Machine using Premium SSD or Ultra Disk for all Operating System Disks and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 99.9%.
For any Single Instance Virtual Machine using Standard SSD Managed Disks for Operating System Disk and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 99.5%.
For any Single Instance Virtual Machine using Standard HDD Managed Disks for Operating System Disks and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 95%.
Composite SLA Of An Application
To get the SLA of an application using multiple Azure services, multiply all of the service’s SLA together (which will yield an SLA lower than the lowest of the services).