Oracle Cloud Infrastructure (OCI) is Oracle's second-generation cloud platform, purpose-built for enterprise performance, security, and Oracle workloads. Unlike first-generation clouds, OCI uses dedicated bare-metal compute, non-blocking networking, and a flat, predictable pricing model designed to eliminate the cost surprises common on other hyperscalers. The key mental model to carry into every OCI design is that everything lives in a compartment, IAM policies are attached to compartments rather than individual resources, and the tenancy itself is always the root compartment — getting that hierarchy right upfront prevents governance pain at scale.
What This Cheat Sheet Covers
This topic spans 17 focused tables and 130 indexed concepts, 128 flashcards. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
A jump-to index of every table row in this cheat sheet.
An interactive map of every table and concept in this topic.
Table 1: Physical Architecture — Regions, Realms, and Availability Domains
OCI's physical hierarchy — realm → region → availability domain → fault domain — governs where resources live, how they replicate, and what resilience guarantees apply. Many "out of capacity" and cross-region connectivity issues stem from misunderstanding which tier a resource belongs to.
| Concept | Example | Description | |
|---|---|---|---|
us-ashburn-1, eu-frankfurt-1 | • Localized geographic area • resources deployed here are isolated from other regions • 45+ commercial regions globally as of 2026. | ||
PHX-AD-1, PHX-AD-2, PHX-AD-3 | • One or more independent data centers within a region • connected by low-latency, high-bandwidth internal network • AD names are randomized per tenancy to balance capacity | ||
FD-1, FD-2, FD-3 within an AD | • Grouping of hardware within an AD • each AD contains exactly 3 fault domains • protects against hardware failures and planned maintenance events | ||
OC1 (commercial), OC2 (US Gov), OC3 (US DoD) | • Logical collection of regions • a tenancy exists in exactly one realm and cannot access regions in a different realm. | ||
Root compartment OCID ocid1.tenancy.oc1..aaaaaa... | • Secure, isolated partition of OCI assigned at sign-up • all resources belong to a tenancy • the root compartment = the tenancy | ||
ocid1.instance.oc1.iad.abuwcljr... | • Oracle Cloud ID — unique identifier for every OCI resource • format ocid1.<type>.<realm>.<region>.<unique_id>. | ||
Customer-specific region identifiers (not public) | • Private OCI region assigned to a single organization • region-specific IDs available only from Oracle support | ||
IAM → cross-region; VCN → regional; compute instance → AD-specific | • IAM resources are global across the realm • most services are regional • DB systems and compute instances are AD-specific |