Getting Started with Oracle Cloud Infrastructure
The physical and logical hierarchy
OCI is organized physically as realm, region, availability domain (AD) and fault domain. A region is a geographic area containing one or more ADs; ADs are isolated, low-latency-connected data centers within a region; fault domains group independent hardware inside an AD. Logically, everything sits under a tenancy (the root compartment), which you subdivide into compartments to organize resources and scope access. Every resource has an OCID, a unique identifier you will see in the console, CLI and API.
Ways to work with OCI
The Console is the browser UI. Cloud Shell is a browser-based, pre-authenticated terminal that already has the CLI and Terraform, plus 5 GB of home directory storage. The CLI, SDKs, REST APIs and Terraform (including Resource Manager) automate the same operations. For the exam, know that the Console region selector changes what you are viewing, not where resources exist.
Free Tier and first steps
Oracle Cloud Free Tier combines Always Free resources (such as small compute instances, Autonomous Databases, object storage and outbound data transfer) with time-limited credits. Always Free resources must be created in your home region, chosen at sign-up and not casually changed. Typical onboarding order: create compartments, set up groups and policies, then provision network (VCN and subnets) before compute.
Trap and rule of thumb
Compartments can nest up to six levels deep, and a compartment cannot be deleted until it is empty. Rule of thumb: every resource you create lives in exactly one compartment, and every compartment traces back to the tenancy root - so a policy placed at the root reaches everything below it.