How to reallocate costs for shared Azure services
The Cost Management and Billing feature of the Azure portal provides very useful information about resource charges. With tagging, individual resources can be collated for reporting and internal billing, e.g., all resources with a Department tag value of HR. This does not affect the billing invoice with Microsoft but supports internal cross-charging for IT services.
There are some resources however that comprise the cloud infrastructure and are shared by multiple cost centres e.g., Active Directory domain controllers. There is a preview feature in Azure which provides cost allocation rules for apportioning charges for a resource to one or more nominated subscriptions, resource groups or tags.
In an Enterprise Scale Landing Zone, the shared infrastructure costs defined in the Management, Identity and Connectivity subscriptions can be allocated to workload landing zone subscriptions, either by distributing evenly or specifying fixed percentages.
More information about how to create custom rules can be found here: