Azure AD Connect is the successor to DirSync and Azure AD Sync and it combines all scenarios these two supported. That said, I wanted to make you aware that DirSync and Azure AD Sync support is ending in a year from now. Azure AD is the recommended way to connect on-premises directory with Office 365 and Azure AD.
- April 13, 2016 -- Windows Azure Active Directory Sync (“DirSync”) and Microsoft Azure Active Directory Sync (“Azure AD Sync”) are announced as deprecated.
- April 13, 2017 -- Support ends. Customers will no longer be able to open a support case without upgrading to Azure AD Connect first.
How to transition to Azure AD Connect:
- If you have an existing DirSync server already running: Upgrade from DirSync
- If you are moving from Azure AD Sync: Upgrade from Azure AD Sync