Difference Between Region, Availability Domain (AD), and Fault Domain (FD) in OCI

1. Region

A region is a specific geographic location where Oracle Cloud Infrastructure (OCI) provides cloud services.

For example, Oracle has regions in locations such as Mumbai, Hyderabad, London, and Frankfurt.

Simple example: If we select the Mumbai Region, our OCI resources can be deployed in that geographic location.

2. Availability Domain (AD)

An Availability Domain (AD) is one or more isolated data centers within an OCI Region.

ADs are designed to provide high availability and fault isolation. If one AD experiences a problem, resources in another AD can continue operating.

Simple example:

Mumbai Region ├── AD 1 ├── AD 2 ├── AD 3

3. Fault Domain (FD)

A Fault Domain (FD) is a grouping of hardware within an Availability Domain that is designed to protect resources from hardware failures and maintenance events.

An AD contains multiple Fault Domains.

Region │ ├── Availability Domain (AD) ├── Fault Domain 1 ├── Fault Domain 2 ├── Fault Domain 3

For example, instead of placing all our application servers in FD1, we can distribute them across FD1, FD2, and FD3. This reduces the impact of a hardware failure or maintenance event affecting one fault domain.