Designing a multi-account cloud chargeback model

WHAT THIS TESTS This evaluates whether you can design governance and data plumbing that produce trustworthy per-team cost attribution at organizational scale, not just enable a billing dashboard.

A GOOD ANSWER COVERS Start with structure: use AWS Organizations so each team or product maps cleanly to accounts or organizational units, which gives a hard, unambiguous attribution boundary even before tags. For finer granularity inside shared accounts, mandate cost-allocation tags such as team, environment, and cost-center. Enforce them rather than trusting goodwill: Service Control Policies can deny resource creation that lacks required tags, and tag policies standardize allowed keys and values to prevent drift like Team versus team. Activate these tags as cost-allocation tags so they appear in billing. For the pipeline, enable the Cost and Usage Report delivered to S3, load it into a warehouse like Athena, Redshift, or BigQuery, and build queries that group cost by account and tag. Allocate shared costs, such as a central logging account or support fees, with a documented split rule, and surface an untagged bucket so gaps are visible and fixable. Schedule the pipeline and publish per-team reports or dashboards.

COMMON WRONG ANSWERS Assuming tags will be applied voluntarily and consistently without enforcement. Forgetting to activate tags for billing, so they never reach the report. Ignoring shared and untagged costs, which makes totals not reconcile. Granting broad IAM so teams can alter each other's resources, muddying attribution and security.

LIKELY FOLLOW-UPS How do you retroactively tag existing resources. How do you handle reserved instance and savings plan discount allocation. Showback versus chargeback.

ONE CONCRETE EXAMPLE An SCP denies any EC2 or RDS launch missing a cost-center tag, tag policies normalize the key, and a nightly job loads the CUR into BigQuery. A scheduled query emits each team's spend plus a shared-services allocation, and an untagged line item drives weekly cleanup.