02. AWS Organizations — Consolidated Billing

Consolidated Billing in AWS Organizations allows you to combine the billing and usage of multiple AWS accounts under one organization.

Feature	Description
One Bill	Receive a single bill for all accounts in your organization.
Combined Usage	Pool the usage of all member accounts to access volume discounts and savings plans.

When multiple accounts share resources under Consolidated Billing:

AWS aggregates the total usage across accounts.
This aggregation helps unlock tiered pricing discounts (e.g., S3, EC2, data transfer).

Scenario	Description
Each account uses 1 TB of S3 data	6 accounts = 6 TB total
AWS applies volume pricing	Discounts apply starting from 5 TB → all accounts benefit

Reserved Instances (RI) and Savings Plans purchased by one account can be shared across all accounts in the organization.

Let's say we have 5 RI in account B.

Account	Reserved Instances	EC2 Instances Launched
A	0	6(2 RI Benfit)
B	5	3

Result:

Total 9 EC2 instances (5 RIs available)
All 5 RIs apply at the organization level
- 3 instances in Account B use RIs
- 2 instances in Account A benefit from remaining RIs
4 instances (unreserved) billed at On-Demand rates

RI & Savings Plan sharing is enabled by default.
You can disable RI/Savings Plan sharing for any member account (including the management account).
Shared Volume Pricing and Shared RI discounts are commonly tested on AWS exams.

Summary

Feature	Description
Combined Usage	Aggregate usage across all accounts for better pricing tiers.
RI/Savings Plan Sharing	Share cost benefits of Reserved capacity organization-wide.
Single Invoice	Simplifies financial management for large multi-account setups.
Optional Control	RI sharing can be disabled per account if needed.