Active Directory, or Microsoft Active Directory (AD), is a service that stores information on network objects in a hierarchical structure. Based on internal permissions and RBAC, administrators and other team members can access and manage this data — including their organization's users, domains, devices, and other network components. Active Directory also stores data on shared servers, user accounts, printers, volumes, and more.
Active Directory is therefore critical for identity and access management (IAM) across organizations with distributed infrastructure and users. It's an indispensable tool in multi-cloud, hybrid cloud, and on-premises environments alike. It's become a critical tool for enterprise networks that demand tighter controls and a clear organizational structure based on users, groups, and granular permissions delegation.
Microsoft first launched Active Directory in early 2000, in conjunction with Windows Server 2000. Since then, Active Directory has continually grown more robust alongside Windows Server and has received numerous updates to deliver deeper management and administration. Active Directory has also given rise to various competitors over the years, with performance being a central topic for sprawling organizations with complex structures.
How does Active Directory work?
Being a Microsoft service, Active Directory is natively compatible with Windows machines and servers — and namely various versions of Windows Server. It was not developed for alternate OSes such as macOS or Linux, but tools exist that help connect such machines to Windows domains. This is a primary use case for Microsoft Active Directory Domain Services (AD DS). Active Directory support in these instances mainly encompasses password policy enforcement and authentication, but group policy support is mostly limited to external tooling that helps bridge the OS gap.
Active Directory virtual components
Active Directory comprises the following software components:
Domains – These describe boundaries between users, groups, and machines within a given organization. Each domain shares a directory database and may be distributed geographically (including virtually). Included are objects such as users, groups, devices, and databases.
Domain trees – These are collections of domains arranged according to their shared root domain — such as
www.company.com. Domain trees account for branch domains, or resources located at URLs that share thecompany.comaddress, such asexample.company.com. These include parent and child domains and tie directly into a company's DNS group policy structures.Forests – These are collections of one or more domain trees that share logic, hierarchical structures, schemas, configurations, and catalogs. Forests can form security boundaries within an organization and are considered "containers." When a company adds a new domain tree to a forest, that tree will be structured differently depending on whether it's the first (root) domain tree or it joins an existing hierarchy.
Organizational units (OUs) – These are containers within a given domain that allow administrators to better organize sensitive resources. You can assign privileges to groups and even entire departments within a company via OUs.
Active Directory physical components
Active Directory also relies on physical components to function properly — such as domain controllers (pushing and managing directory updates) and global catalog servers (providing rapid reference to and copies of domain objects). These domain controllers come in a couple of different flavors. First, you have operations masters that ensure all controllers are in sync while performing important backend administrative tasks.
Second, you have read-only controllers that contain immutable copies of Active Directory data — typically in locations or on networks without stringent security controls. This helps prevent privilege escalation and incidents outside of the main corporate network.
Active Directory fundamentals
All Active Directory class objects and resources follow a standardized schema that defines naming conventions and any important constraints. Everything contained within the directory is indexed to be discoverable by users with required permissions. Replication services take that directory data and make it available across the network (or wide-area network), while ensuring all changes are distributed accordingly. This keeps the directory current.
There are numerous services designed for Microsoft Active Directory. These provide the following functions:
User, system, and resource management across connected domains
Certificate management and data encryption
Lightweight directory creation for applications and services that don't require full Active Directory management
Federated access across clouds and other businesses, powered by claim-based authentication and single sign-on (SSO)
Usage restrictions for sensitive and proprietary content according to group, role, or individual user
Administrators are typically authenticated through a service such as the NT LAN Manager (NTLM) suite or Kerberos — which is generally considered more secure and integrates with the Lightweight Directory Access Protocol (LDAP). Next comes authorization through a service such as Microsoft Entra ID.
Once a user is authorized, they can access any stored directory information across the network. This requires simple credentials and tokenization to ensure that a given administrator (on a trusted computer) is who they claim to be. These power users are free to set policies through PowerShell, Active Directory Administrative Center, and Active Directory Users and Computers. Both Active Directory tools grant control through a GUI, while PowerShell is a scripting language used through a command-line interface (CLI).
What are the benefits of Active Directory?
Microsoft Active Directory is popular for good reason. Here are the advantages it offers for enterprise organizations at scale:
Centralized permissions and object management without the need for multiple tools (on Windows machines) or complex processes
Greater control and visibility for internal enterprise environments
Enhanced security and compliance through smarter, RBAC-based access policies for data and other resources
Simplified resource sharing — such as printers and files — across the network without needing supplemental tooling
Granular management for users, groups, and business units
Improved troubleshooting and logging
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Does HAProxy support Active Directory?
Yes! HAProxy One supports features such as SAML single sign-on (SSO) for your Azure Active Directory and Microsoft Entra ID-supported environments. To learn more about Active Directory support in HAProxy, check out our blog, HAProxy Enterprise Offers SAML-based Single Sign-On.