What’s changing?

Starting August 1st, Azure Container Registry (ACR) will update its behavior regarding the deletion and re-creation of registries. ACR will prevent the reuse of a subdomain name, e.g. abc123.azurecr.io, for a period after the resource is deleted. This updated behavior enhances security and prevents subdomain takeovers by automatically reserving registry names during the creation of the ACR resource, without requiring any additional action or configuration from customers. 

Once a resource name is reserved, it remains reserved from the moment of creation and throughout an extended period following the deletion of the resource (referred to as a cooldown period). During this cooldown period, subscriptions not associated with the original Azure AD tenant that created the resource will be unable to use the same name for a new registry. After the cooldown period concludes, the name reservation is lifted, allowing any subscription to create a registry with the previously reserved name. 

Customer impact

Most customers will not be impacted by this update. If you delete a registry, you can create a new one with the same name within the cooldown period, provided the subscription belongs to the same Azure Active Directory (AAD) tenant. This ensures a seamless experience for customers who routinely create –> delete –> recreate resources with the same name within the same AAD tenant for testing and production workflows. 

The name reservation feature guarantees that customers have exclusive rights to a resource name between its deletion and subsequent recreation, preventing other customers from claiming the same name during this interval. 

Learn more

To learn more about Azure Container Registry: Azure Container Registry documentation 
To learn more about the different ways to avoid dangling domains and subdomains takeover: Prevent dangling DNS entries and avoid subdomain takeover 
To learn more about the one-to-many relationship between an Azure AD tenant and an Azure subscription: Azure subscriptions and Azure AD Tenants

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