question

Hello Lisa ,

Please find the answers. Azure AD domain services is a managed Active Directory instance with the main goal to provide Legacy authentication capabilities (for legacy apps which use Kerberos , NTLM) in the cloud so that anyone who would like to completely migrate to Azure and remove on-premise active directory could life and shift the on-prem application servers as is , and have the benefits of legacy auth protocols in the cloud. So as for your answer , please find the below.

• Does Azure Active Directory Domain Services (AADDS) support custom schema extensions
  

  • No , It does not support custom schema extensions. Extending schema is not a permitted operation on the AAD Domain Services instance.

    
    
• Would you describe AADDS as a globally shared AD Forest with a managed domain for my org?
  

  • Not exactly . Each instance is unique to one customer and part of a larger globally shared AD in the backend. Whenever you enable Azure AD domain services, a new restricted Domain Controller for the domain name you have provided during initial configuration , is created. The difference from on-premise AD is that you do not get complete flexibility to change and modify the domain controller settings as you would be able to do in your on-prem Domain controller. This is because it was never created for making it a feature-by-feature replacement for on-premise AD. If you require completely similar control in the cloud then we suggest you to create Azure VMs and promote them to domain controllers . You may have to setup a site-to-site VPN for the same between your on-prem location and the Azure using Azure gateway / Azure VPN.

Hope this clarifies your queries. I have added some links to my answer , please check the same. Also I would encourage you to go through the complete FAQ for the Azure AD domain Services and I am sure a lot of your queries could get answered automatically. In case the above information in the post helps you , please do mark it as answer so that it can help others in the community searching for same answers.

Thank you.