Azure Active Directory is the next evolution of identity and access management solutions for the cloud. Microsoft introduced Active Directory Domain Services in Windows 2000 to give organizations the ability to manage multiple on-premises infrastructure components and systems using a single identity per user.
Azure AD takes this approach to the next level by providing organizations with an Identity as a Service (IDaaS) solution for all their apps across cloud and on-premises.
I recommend AADS only if you have on premise resources (shares, apps, etc) that you would like to control and access using your cloud identity. Also I would recommend the managed service, Azure Active Directory Domain Services.
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