AD Connect will sync your on-premises AD or AWS Managed Active Directory with Azure Active Directory. This allows you to provide a common identity for your users for Office 365, Azure, and SaaS applications integrated with Azure AD.

AD Connect Sync Features

Use Azure AD connect with ADFS to provide single sign on for Office365 users (password hash sync, pass-through authentication, federation with AD FS, or federation with PingFederate)
Filtering options on what to sync, filtering based on domains, OUs, or attributes.
Password hash synchronization synchronizes the password hash in Active Directory to Azure AD. The end-user can use the same password on-premises and in the cloud but only manage it in one location. Since it uses your on-premises Active Directory or AWS AD as the authority, you can also use your own password policy.
Password writeback will allow your users to change and reset their passwords in the cloud and have your on-premises password policy applied.
Device writeback will allow a device registered in Azure AD to be written back to on-premises Active Directory so it can be used for conditional access
The prevent accidental deletes feature is turned on by default and protects your cloud directory from numerous deletes at the same time. By default it allows 500 deletes per run. You can change this setting depending on your organization size.

Amazon EC2 running Microsoft Windows Server is a fast and dependable environment for deploying applications using the Microsoft Web Platform. Amazon EC2 enables you to run compatible Windows-based solutions on AWS' high-performance, reliable, cost-effective, cloud computing platform.