AWS Directory Service is a series of directory services included Microsoft Active Directory in the cloud. There are numerous flavors: AD Connector, AWS Directory Service for Microsoft Active Directory (Enterprise Edition), Cognito & Simple AD
AD Connector and Microsoft Active Directory (Enterprise Edition) support standard Active Directory administration tools and take advantage of built-in Active Directory features such as Group Policy, trusts, and single sign-on.
AD Connector connects existing AD implementation with the AWS cloud which enables existing security polices like password expiration/history and account lockout with existing RADIUS-based MFA to manage resources like EC2 instances and applications like WorkSpaces, WorkDocs or WorkMail. AD Connectors and on-premises domains have a 1-to-1 relationship. It does not support caching, trust relationships, VPN/DX, SQL server integration.
Simple AD is a Microsoft Active Directory–compatible directory from AWS Directory Service using Samba 4 for use cases of less than 5000 users. This service does NOT support MFA or additional AD servers, support trust relationships with AD, or transfer FSMO roles for AD management. There are two sizes: small for up to 500 users and large for up to 5000 users.
Managed Microsoft Active Directory
Managed Microsoft Active Directory, which used to be called the “Enterprise Edition” is the same feature-rich Microsoft Active Directory just hosted on AWS. This is a managed service like RDS but better; it’s multi-AZ, is patched, rotated and snapshotted by default. All you need to do is manage the implementation of it for the org and it’s a good choice for more than 5,000 users.
To use on-prem and cloud directory information interchangably, you can set up a trust relationship set up between an AWS hosted directory and your on-premises directories using AD two-way Forest trust; trust is NOT replication more like two parts of the same directory. AD one-way trust is also possible.. but not sure why one would do that. To replicate data between on-prem and cloud AD, perhaps for a DR scenario, you need to replicate the directory to an EC2 instances then set up two-way Forest Trust with Managed Microsoft AD. (not clear why you can’t replicate with Managed AD directly)
Amazon Cloud Directory is a great choice when you need to build application directories such as device registries, catalogs, social networks, organization structures, and network topologies.
You can also use Amazon Cognito when you need to create custom registration fields and store that metadata in your user directory. This fully managed service scales to support hundreds of millions of users while fully supporting federated identities.
Scalable? Cloud Directory
Have AD and wanna use it on AWS? AD Connector
More than 10 directories and 5 snapshots per each directory? Call AWS for limit increase.
Need something AD compatible? Managed Microsoft AD, AD Connector, Simple AD
Greater than 5000 users? Managed Microsoft AD
Simple LDAP? Cloud Directory