Oracle Cloud Infrastructure (OCI) is a cloud computing platform that enables you to build and run a wide range of applications in a highly available, high-performance environment. OCI offers a variety of services, including Database, Data and AI, Analytics, and Core infrastructure.

Users can access these services through Oracle Cloud Infrastructure Identity and Access Management (IAM). After authentication, users can choose a region based on several factors: 

1. The region closest to the user, which ensures low latency and the highest performance.
2. Many countries have strict data residency requirements that require compliance.
3. New cloud services are made available based on regional demand, regularity compliance reasons, resource availability, and other factors.

The main components of the OCI architecture are as follows:

• Region: This is the localized geographic area comprising one or more availability domains.
• Availability Domain: These are one or more fault-tolerant data centers located within a region; they are connected to each other by a low latency, high-bandwidth network. Each availability domain generally has three fault domains.
• Fault Domains: These are groupings of hardware and infrastructure within an availability domain, designed to provide anti-affinity.
• Oracle Real Application Clusters (RAC): This allows customers to run a single Oracle Database across multiple servers in order to maximize availability and enable horizontal scalability, while accessing shared storage. Oracle RAC provides end-to-end protection of customer databases by safely replaying transactions during outages without impacting end user experience.
• Data Guards: These can be used to keep data synchronized and avoid a single point of failure. Data Guards connect a RAC Database in a Fault Domain within an Availability Domain to another RAC Database in a different Availability Domain. 

When an application is built, a software-defined virtual network is created. In an OCI region, there are three availability domains, and each availability domain has three fault domains. The fault domains contain the application tier and database tier. Both the application tier and the database tier are replicated across fault domains. All application tiers available in a fault domain are grouped together in one subnet within the availability domain. After choosing a particular region, users can access all the services provided by Oracle Cloud Infrastructure.

• Oracle Cloud Infrastructure (OCI)
• Regions and Availability Domains
• Cloud Guard