Active Directory alternatives: what replaces AD, and what does not

Active Directory is not one product but a bundle of jobs: a directory that stores users and computers, Kerberos for domain logon, LDAP for directory queries, DNS for the domain, and Group Policy for managing Windows machines. An "Active Directory alternative" means different things depending on which of those jobs you actually need to replace.

Short answer: there is no drop-in open-source replacement for the whole bundle. For cloud single sign-on to applications, Entra ID or an open-source identity provider such as Casdoor replaces AD's identity role. For Windows domain join and Group Policy, Samba AD or Entra Domain Services is the closer match. For Linux identity, FreeIPA or OpenLDAP is the usual choice.

The four jobs AD does

AD DS is the part that provides all five. AD CS, AD FS and AD LDS are separate roles with their own replacements; most organizations asking about alternatives only need the identity and SSO part.

Which alternative fits which job

Microsoft Entra ID

Entra ID is Microsoft's cloud identity provider. It signs users in to Microsoft 365, thousands of SaaS applications and apps you register yourself, over SAML, OpenID Connect and OAuth 2.0. It is the natural choice if your organization already runs Microsoft 365 and your users are in Entra ID already.

It does not replace a domain controller. On-premises servers still need AD DS or Entra Domain Services for domain join, Group Policy and Kerberos. Entra ID is the identity and SSO layer, not the Windows management layer.

Samba AD DC

Samba can run as an Active Directory domain controller, including Kerberos, LDAP, DNS and Group Policy support. It is the only open-source option that lets Windows machines join a domain and be managed with Group Policy.

The trade-offs are operational. Samba's AD implementation covers the common cases but not every Microsoft extension, and the tooling is less polished than Microsoft's. Choose it when you need AD-compatible domain services and want to avoid Windows Server licences; keep AD if you depend on advanced Windows features.

FreeIPA

FreeIPA is an integrated identity management system for Linux and Unix environments. It combines 389 Directory Server, MIT Kerberos, DNS, a certificate authority and SSSD, with a web UI and CLI for managing users, groups, hosts and access rules.

It is the closest thing to "AD for Linux", but it is not AD-compatible: Windows clients cannot join it as a domain, and it does not do Group Policy. A trust with AD is possible when the two must coexist. Choose FreeIPA when most of your machines are Linux and you want Kerberos and DNS in one place.

OpenLDAP

OpenLDAP is a directory server, not an identity platform. It stores entries and answers LDAP queries, and applications authenticate by binding with a username and password. It has no Kerberos, no SSO, no login pages and no MFA.

It remains the right answer for legacy applications and appliances that only speak LDAP, especially when you want a small, stable directory. Running OpenLDAP alone means every application still shows its own password prompt.

JumpCloud

JumpCloud is a cloud directory that also manages devices. It provides user and group management, LDAP and RADIUS endpoints, SSO to applications, and agents for Windows, macOS and Linux that apply policies and commands.

It is a good fit for small and mid-sized organizations that want to retire on-premises AD without building a Windows Server estate. It is a commercial service, so evaluate the per-user cost against what you would spend running your own directory.

Casdoor as the application identity layer

Casdoor is an open-source identity provider, not a domain controller. It signs users in to applications over OpenID Connect, SAML 2.0 and CAS, serves LDAP for legacy apps and network devices, and syncs users from AD, LDAP, Entra ID, Okta and Keycloak.

That makes it a replacement for the SSO part of AD, not for domain join or Group Policy. In a common setup, AD or Entra ID stays as the source of employee accounts, and Casdoor sits in front of the applications that need SSO, MFA, organizations or self-service login. Self-host it for free, or run a dedicated instance on Casdoor Cloud.

A migration checklist

1. Inventory the protocols. List every application and appliance and whether it uses SAML, OIDC, LDAP, Kerberos or a Windows domain.
2. Pick one source of truth. Decide whether AD, Entra ID or the new identity provider owns the account; sync from it rather than creating a second copy.
3. Pilot one group. Move a small team and one application first, with a rollback path.
4. Keep AD until the last Windows dependency is gone. File servers, print servers and legacy appliances often outlive the SSO migration.
5. Decommission in stages. Disable accounts, then remove domain trusts, then retire the domain controllers.

FAQ

Can I replace Active Directory with Entra ID entirely? For application SSO, yes. For Windows domain join, Group Policy and Kerberos on on-premises servers, no: you still need AD DS or Entra Domain Services.

Is Samba a full Active Directory replacement? It is the closest open-source option and supports domain join, Kerberos, LDAP, DNS and Group Policy for common cases. Advanced Microsoft features and some management tooling are not covered.

Is FreeIPA compatible with Active Directory? No. FreeIPA is an integrated Linux identity system; it can establish a trust with AD but Windows clients cannot join it as a domain.

What is the best open-source alternative to Active Directory for SSO? Casdoor or Keycloak for applications, and FreeIPA or Samba for machine identity. The right choice depends on whether you need domain join or only single sign-on.

Can I keep Active Directory and add SSO on top? Yes, and it is the common path: keep AD as the account source, sync users to an identity provider such as Casdoor, and use OIDC or SAML for the applications.