Identity is the foundation of every other security control, so choosing where it lives matters. Microsoft Entra ID (formerly Azure AD) and traditional on-premise Active Directory solve overlapping problems in very different ways. They are not direct replacements, and many businesses run both. Here is how to decide.
They are not the same thing
On-premise Active Directory is a directory and authentication service built around LDAP, Kerberos, and Group Policy for managing Windows domains. Entra ID is a cloud identity platform built around modern protocols like SAML, OAuth, and OpenID Connect for web and SaaS apps. The terminology overlaps, but the architecture does not.
Cost and maintenance
On-premise AD requires domain controllers you must patch, back up, and protect physically. Entra ID is a managed service with no servers to maintain. For a small business without dedicated infrastructure staff, the operational savings of cloud identity are significant.
Security model
Entra ID brings Conditional Access, risk-based sign-in policies, and built-in MFA that are difficult and expensive to replicate on-premise. On-premise AD, however, gives you Group Policy and tight control over domain-joined Windows machines that the cloud handles differently through Intune.
Application compatibility
Legacy line-of-business apps that rely on Kerberos or LDAP need on-premise AD. Modern SaaS applications integrate natively with Entra ID. If your workloads are mostly Microsoft 365 and cloud apps, Entra ID alone may suffice; if you run legacy Windows software, you likely still need AD.
The hybrid middle ground
Most established businesses land on a hybrid model: keep on-premise AD for domain-joined machines and legacy apps, and sync identities to Entra ID with Entra Connect for cloud and SaaS access. Users get one identity; you keep the capabilities of both worlds.
How to choose
A new, cloud-first company should start with Entra ID and avoid running domain controllers at all. An established business with Windows servers and legacy apps should run hybrid. Pure on-premise-only is increasingly rare and hard to justify for most SMEs.
Decide based on your applications and staff, not hype. For most growing businesses, cloud-first or hybrid identity is the pragmatic answer.
Korur Security Team
Korur Security Team