Fault Domains and Fault Levels: AWS vs. Azure
What’s a Fault Domain?
A fault domain is a part of a data center (like a rack of servers or a whole room) where, if something breaks (like power or network), only that section is affected. The main idea: failures don’t “spill over” and mess up everything else[1].
What’s a Fault Level?
A fault level is just a group of fault domains. Think of it as a bigger box containing smaller boxes (fault domains).
How AWS and Azure Do It Differently
| Cloud |
Fault Level (Big Group) |
Fault Domain (Small Group) |
Extra Concepts |
| AWS |
Region (e.g., us-east-1) |
Availability Zone (e.g., us-east-1a) |
— |
| Azure |
Region (e.g., East US) |
Availability Zone or Fault Domain |
Update Domain |
- AWS:
- A Region is the big area (fault level), made up of multiple Availability Zones (fault domains).
- If one zone fails, others keep working[1].
- Azure:
- Uses both Availability Zones (like AWS) and Fault Domains (inside an Availability Set).
- Fault Domains are racks or groups of servers with shared power/network.
- Azure also has Update Domains—these are for planned maintenance, so not all your servers reboot at once[2][3][5][6].
In short:
- Both AWS and Azure split their data centers to limit failures.
- AWS calls the big group a Region, small group an Availability Zone.
- Azure uses Regions too, but also has Fault Domains (hardware groups) and Update Domains (for updates), so failures and maintenance don’t take everything down at once.