Availability and Resiliency¶
To ensure high availability, Azure provides various tools and strategies to mitigate failures, ranging from hardware faults to entire datacenter outages.
Availability Options¶
| Option | SLA | Protection Scope | Cost Impact |
|---|---|---|---|
| Single VM | 99.9% (Premium SSD) | No built-in redundancy; single-instance SLA only. | Base cost |
| Availability Sets | 99.95% | Fault and update domain faults. | No extra cost |
| Availability Zones | 99.99% | Entire datacenter failure. | Potential data transfer cost |
| VMSS | Depends on config | Automatic scaling and high availability. | Scale-out costs |
Availability Zone vs Availability Set Architecture¶
Availability Zones are separate datacenters in one region. Availability Sets distribute VMs across fault and update domains within a datacenter; they do not protect against full datacenter failures.
graph TD
Region[Azure Region]
Region --> AZ1[Zone 1 Datacenter]
Region --> AZ2[Zone 2 Datacenter]
Region --> AZ3[Zone 3 Datacenter]
Region --> DC1[Single Datacenter]
DC1 --> ASet[Availability Set]
ASet --> FD1[Fault Domain 1]
ASet --> FD2[Fault Domain 2]
ASet --> UD1[Update Domain 1]
ASet --> UD2[Update Domain 2]Note
Fault Domains (FD) protect against physical hardware failures, while Update Domains (UD) protect against scheduled maintenance.
Tip
Virtual Machine Scale Sets (VMSS) allow you to create and manage a group of load-balanced VMs automatically.