Active Directory and Microsoft Entra ID: The Foundation of a Modern Hybrid Cloud Environment

For many organizations, the first meaningful step into the cloud is not migrating a server, deploying a new application, or creating an Azure subscription.

It is connecting identity.

Most established companies already operate Windows Server Active Directory Domain Services, commonly called Active Directory or AD. It authenticates users to workstations, servers, file shares, printers, applications, and other resources inside the corporate network.

At the same time, many of those companies already use Microsoft 365 for Exchange Online, Outlook, Teams, SharePoint Online, and OneDrive. That means a Microsoft Entra ID tenant already exists, whether the organization has intentionally designed a cloud identity strategy or not.

The result is frequently two separate identity environments: an on-premises Active Directory account used for corporate computers and local resources, and a Microsoft Entra ID account used for Microsoft 365 and cloud applications.

The usernames may look identical. The passwords may even have been manually configured to match. Technically, however, they are still separate identity objects with separate lifecycle processes.

Connecting those environments creates a hybrid identity architecture in which Active Directory and Microsoft Entra ID work together.

This is one of the most important foundations an organization can establish before accelerating its broader cloud-adoption strategy.

Active Directory and Microsoft Entra ID Are Related, but They Are Not the Same

Active Directory and Microsoft Entra ID both provide identity and authentication capabilities, but they were designed for different technology models.

Active Directory Domain Services

Active Directory Domain Services was designed for traditional Windows enterprise networks. It provides Kerberos and NTLM authentication, LDAP directory services, domain-joined computers, Group Policy, computer accounts and domain trusts, Windows-integrated authentication, security groups, organizational units, and on-premises application integration.

AD remains critical for organizations that operate Windows servers, legacy applications, traditional file shares, manufacturing systems, or other workloads that depend on domain membership and established Windows authentication protocols.

Microsoft Entra ID

Microsoft Entra ID, formerly Azure Active Directory, is Microsoft's cloud identity and access-management platform. It provides authentication and authorization for Microsoft 365, Azure, thousands of software-as-a-service applications, and custom cloud applications.

Its capabilities include modern authentication, OAuth 2.0 and OpenID Connect, SAML single sign-on, multifactor authentication, Conditional Access, Identity Protection, Privileged Identity Management, enterprise application access, device identity, application registrations, and workload or managed identities.

Microsoft Entra ID is not a cloud-hosted domain controller, and it does not replace every Active Directory function.

The two platforms are complementary. Active Directory continues to support traditional on-premises resources while Entra ID becomes the identity control plane for Microsoft 365, Azure, SaaS applications, and modern security controls.

Microsoft 365 Means Microsoft Entra ID Is Already There

When an organization subscribes to Microsoft 365, Microsoft automatically creates or associates the service with a Microsoft Entra tenant. That tenant stores the users, groups, applications, and authentication information used to access Microsoft cloud services.

This means many companies already have Entra identities before they begin a formal cloud migration.

A common environment looks like this:

ON-PREMISES ACTIVE DIRECTORY

user@company.com
Used for:
- Windows sign-in
- File shares
- Internal applications
- VPN
- Servers

MICROSOFT ENTRA ID / MICROSOFT 365

user@company.com
Used for:
- Exchange Online
- Microsoft Teams
- SharePoint Online
- OneDrive
- SaaS applications

Although both accounts display the same address, they may have no technical relationship.

Human Resources or IT creates the employee in Active Directory. Someone then creates a second account in the Microsoft 365 admin center. Password changes occur independently. Terminations require separate actions. Group memberships, names, phone numbers, departments, and job titles can drift apart.

This duplicate administration works when an organization is small. It becomes increasingly fragile as the company grows, adopts more cloud applications, or faces stronger security and compliance requirements.

Hybrid Identity Creates One Connected User Lifecycle

A hybrid identity deployment connects the on-premises Active Directory forest to the organization's existing Microsoft Entra tenant.

The architecture typically uses either Microsoft Entra Cloud Sync, using lightweight provisioning agents and cloud-managed synchronization configuration, or Microsoft Entra Connect Sync, using a dedicated synchronization server with the full synchronization engine.

These services synchronize selected users, groups, contacts, and attributes from Active Directory into Microsoft Entra ID.

For synchronized users, Active Directory is commonly the authoritative source for core identity attributes. Changes made to the user on-premises are synchronized to Entra ID and become available to Microsoft 365 and other connected services.

This gives the organization a controlled identity lifecycle: create the employee in Active Directory, place the user in the correct organizational unit and groups, synchronize the identity to Entra ID, assign Microsoft 365 or application licenses, apply cloud access and security policies, and disable or remove the source identity when the employee leaves.

Hybrid identity does not eliminate identity administration, but it removes much of the duplicate identity creation and unmanaged drift.

Connecting to an Existing Microsoft 365 Tenant Requires Careful Planning

Installing a synchronization agent and clicking Next is not an identity strategy.

When Microsoft 365 accounts already exist, the implementation must correctly link each on-premises AD user to the corresponding cloud account. A poorly planned deployment can create duplicates, produce synchronization errors, overwrite attributes, or associate the wrong AD object with the wrong Microsoft 365 identity.

This is why Fletcher Technology Group approaches an existing-tenant integration as an identity-reconciliation project, not merely a software installation.

How Fletcher Technology Group Connects Active Directory to an Existing Entra Tenant

Our implementation methodology is designed to protect existing Microsoft 365 identities, mailboxes, Teams data, licenses, and application access while establishing Active Directory as the appropriate source for synchronized identity information.

1. Discover the Existing Identity Environment

We begin by assessing both directories. The Active Directory assessment includes forests and domains, functional levels, user and group counts, OU structure, UPN suffixes, proxyAddresses values, mail attributes, service and privileged accounts, stale identities, existing synchronization products, Exchange dependencies, domain-controller health, DNS, and network connectivity.

The Microsoft Entra and Microsoft 365 assessment includes verified custom domains, cloud-only users, administrative accounts, guests, Microsoft 365 groups and distribution objects, UPNs, primary SMTP addresses, licensing assignments, authentication methods, Conditional Access policies, enterprise applications, tenant synchronization state, source-anchor values, and duplicate or conflicting attributes.

The objective is to establish a reliable mapping between the existing AD identities and the existing Microsoft 365 identities before synchronization exports are allowed.

2. Determine the Source of Authority

A hybrid environment needs clear ownership of identity attributes. For synchronized users, Active Directory typically becomes the authoritative source for attributes such as display name, UPN, email aliases, department, job title, manager, office, phone number, and group relationships.

Once an object is synchronized, many of its properties can no longer be managed directly in the Microsoft 365 or Entra portals because those properties are sourced from Active Directory. That behavior is expected, but it must be understood before implementation.

We document which identities will be sourced from AD, which identities remain cloud-only, which attributes synchronize, which attributes remain managed in the cloud, how employee lifecycle events are processed, and which team owns each action.

3. Standardize the User Principal Name

A frequent issue is an internal Active Directory namespace that does not match the organization's public Microsoft 365 domain.

On-premises AD sign-in:
user@company.local

Microsoft 365 sign-in:
user@company.com

A nonroutable AD suffix such as .local should generally not become the user's Entra sign-in name.

FTG evaluates the existing namespace and, where appropriate, adds the verified public domain as an alternative UPN suffix in Active Directory. Users can then be updated to a consistent sign-in name such as user@company.com.

UPN changes must still be tested because they can affect scripts, applications, cached credentials, VPN clients, mobile devices, certificates, and other systems that incorrectly treat a user-readable sign-in name as an immutable identifier.

4. Clean the Directory Before Synchronization

Identity synchronization exposes directory-quality problems that may have accumulated for years, including duplicate proxyAddresses, duplicate UPNs, invalid email-address formats, stale accounts, shared accounts represented as users, conflicting contacts and groups, missing required attributes, inconsistent naming, mail attributes assigned to the wrong object, and old accounts that conflict with current employees.

Microsoft provides the IdFix tool to identify many formatting and duplication problems before synchronization. FTG combines automated analysis with manual identity review, resolving conflicts at the source rather than allowing a production synchronization cycle to become the discovery process.

5. Reconcile Existing Cloud Accounts With AD Accounts

When an on-premises object is introduced to Microsoft Entra ID, the service attempts to determine whether it corresponds to an existing cloud object. Matching can involve the immutable source anchor, UPN, primary SMTP address, and other synchronization matching logic.

A correct match converts the existing cloud-managed user into a synchronized identity while preserving the Microsoft 365 account and its associated services. A failed match can create a second user. A wrong match can link the incorrect identities.

Where automatic matching cannot be used safely, source-anchor remediation or a controlled hard-match process may be required. Hard matching is an exception procedure, not something that should be applied broadly without understanding the consequences.

6. Select Entra Cloud Sync or Entra Connect Sync

Microsoft now provides two primary synchronization platforms.

Microsoft Entra Cloud Sync uses lightweight agents installed in the on-premises environment while most configuration and orchestration are managed from Microsoft Entra. It is attractive because it provides a lightweight agent model, cloud-managed configuration, multiple-agent resiliency, support for multiple and disconnected AD forests, reduced dependency on a single full synchronization server, and a modern management approach.

Microsoft Entra Connect Sync remains appropriate for environments that require capabilities or topologies supported by its full synchronization engine. It provides detailed synchronization-rule control, a local metaverse and connector spaces, extensive filtering and attribute-flow options, staging-server functionality, established hybrid identity support, and mature troubleshooting tooling.

FTG does not select a synchronization platform based on which product is newer. We select it based on topology, Exchange requirements, writeback requirements, forest design, attribute needs, operational model, and future roadmap.

7. Choose the Authentication Method

Directory synchronization and user authentication are related, but they are separate architecture decisions.

Password Hash Synchronization synchronizes a nonreversible hash derived from the user's AD password hash to Microsoft Entra ID. Cloud authentication then occurs directly in Entra ID. This is generally the simplest and most resilient hybrid authentication model because cloud sign-in does not depend on an available on-premises agent or federation service.

Pass-Through Authentication validates a user's password against on-premises Active Directory through authentication agents. This may be selected when an organization has a specific requirement for cloud sign-ins to validate against AD in real time, but it increases dependency on agents, domain controllers, network connectivity, and agent health.

Federation redirects authentication to an external identity provider such as Active Directory Federation Services. Federation may still be justified by specialized authentication requirements, but it introduces more infrastructure, certificates, dependencies, monitoring, and recovery planning.

8. Define a Controlled Synchronization Scope

FTG does not begin by synchronizing the entire directory. We define a pilot scope using selected organizational units, groups, or synchronization filters.

The pilot normally includes IT administrators responsible for the project, technically capable test users, representative departments, users with existing Exchange Online mailboxes, users with Teams, OneDrive, and SharePoint usage, and different account and group scenarios.

The initial scope generally excludes Tier 0 or highly privileged AD accounts that do not need cloud access, service accounts, shared technical identities, stale users, disabled legacy accounts, test objects, application-specific accounts, and objects with unresolved attribute conflicts.

The goal is not to synchronize everything that exists. It is to synchronize every identity that has a valid business requirement.

9. Validate Changes Before Export

With Entra Connect Sync, staging mode allows the synchronization engine to import and calculate changes without exporting them to Active Directory or Entra ID. This is a critical control for an existing tenant.

Before production export, FTG reviews which new objects would be created, which cloud users would be matched, which attributes would change, which objects would be deleted or placed out of scope, whether duplicate-attribute errors exist, whether the selected source anchor is correct, and whether the synchronization scope matches the approved design.

Preview the identity changes before allowing the platform to make them.

10. Synchronize a Pilot and Validate the User Experience

After the design and preview are approved, FTG enables synchronization for the pilot population.

We validate that existing Microsoft 365 mailboxes remain attached to the correct users, Teams and SharePoint access continue to function, licenses remain assigned, password changes synchronize as expected, UPNs are correct, group memberships are correct, new employees can be provisioned through the defined process, disabled users lose access as designed, sign-in logs show the expected authentication method, duplicate accounts are not created, and support personnel understand where attributes must be changed.

Only after the pilot succeeds do we expand the synchronization scope.

11. Establish Resiliency and Monitoring

Identity synchronization becomes production infrastructure. It requires monitoring, support ownership, and recovery planning.

Depending on the platform, FTG may implement multiple Cloud Sync agents, an Entra Connect staging server, Microsoft Entra Connect Health, synchronization-error alerting, agent and server monitoring, documented recovery procedures, configuration backups, change control, emergency access accounts, periodic identity reconciliation, and synchronization service-account governance.

Cloud-only emergency access accounts should be maintained so administrators are not entirely dependent on on-premises AD or the normal hybrid authentication path during an outage.

Why Hybrid Identity Is a Critical First Step in Cloud Adoption

Identity is the common control plane across almost every cloud initiative.

An organization can deploy Azure subscriptions, SaaS applications, remote-work solutions, security tools, and endpoint-management platforms independently. Without a coherent identity strategy, each deployment creates another account store, another access process, and another operational gap.

One Identity Across On-Premises and Cloud Resources

Users can retain a consistent identity while accessing domain-joined workstations, Windows servers, file shares, Microsoft 365, Azure resources, SaaS applications, custom web applications, and remote-work platforms.

Centralized Cloud Security Controls

Once identities are represented in Entra ID, the organization can begin applying cloud-native protections such as multifactor authentication, Conditional Access, risk-based sign-in policies, Identity Protection, Privileged Identity Management, access reviews, single sign-on, self-service password reset, and authentication-method policies.

Better Employee Lifecycle Management

A connected identity lifecycle reduces the risk that terminated employees remain active in one environment because only the other account was disabled. New employees receive cloud access from the established workflow, name and department changes propagate consistently, group-based licensing can be automated, and disabled source accounts trigger corresponding cloud restrictions.

A Foundation for Intune and Modern Device Management

Hybrid identity frequently becomes the bridge toward modern endpoint management. Organizations can progress from traditional domain-joined devices to hybrid Microsoft Entra joined devices, and then to Microsoft Entra joined and Intune-managed devices where appropriate.

Easier SaaS and Application Integration

Entra ID can provide single sign-on to many third-party applications through SAML, OpenID Connect, OAuth, password-based SSO, or application proxy scenarios. Once AD identities are synchronized, existing employees can use their established enterprise identities for new cloud applications instead of receiving another username and password.

A Controlled Path Away From Legacy Dependencies

Hybrid identity does not require an organization to eliminate Active Directory immediately. The company can continue operating file servers, domain-based applications, Group Policy, Kerberos workloads, legacy authentication, and Windows Server infrastructure while adopting Microsoft 365, Azure, modern authentication, Conditional Access, cloud applications, Intune, and Zero Trust principles.

Common Implementation Mistakes

Synchronizing Before Cleaning the Directory

Duplicate UPNs and proxy addresses should be resolved before production export.

Assuming Same Username Means Same Identity

Two accounts with the same visible address are not automatically linked. Matching must be validated.

Synchronizing Every Account

Service accounts, stale identities, privileged accounts, and technical users should not be synchronized without a defined requirement.

Changing the Source Anchor Without Understanding It

The source anchor is the durable link between the AD object and the Entra object. An incorrect change can break identity matching.

Treating Synchronization as Full Bidirectional Replication

Many synchronized attributes remain authoritative on-premises. Administrators need to know where each property must be managed.

Deploying Federation Without a Business Requirement

Federation adds infrastructure and failure points. It should solve a documented requirement.

Ignoring Emergency Access

Organizations need cloud-only administrative accounts for scenarios in which AD, synchronization, or the primary authentication path is unavailable.

Enabling Conditional Access Without Exclusions and Testing

Conditional Access is powerful. A poorly planned policy can lock out administrators or interrupt critical service accounts.

Failing to Operationalize the Platform

The synchronization server or agent cannot become an unmonitored appliance that nobody owns. Identity is production infrastructure.

Hybrid Does Not Mean Permanent

A hybrid identity architecture is not necessarily the final destination.

For some organizations, Active Directory will remain a long-term requirement because of legacy applications, servers, operational technology, or regulatory constraints.

For others, hybrid identity is a transition state toward Microsoft Entra joined endpoints, cloud-native authentication, SaaS applications, Azure-hosted workloads, reduced dependence on domain controllers, retirement of legacy protocols, and eventual Active Directory consolidation or decommissioning.

The architecture should support both possibilities.

FTG designs hybrid identity so the organization receives immediate operational value without blocking future cloud-native modernization.

The FTG Hybrid Identity Outcome

A successful project should deliver more than a functioning synchronization cycle.

The desired outcome is a documented, supportable identity platform with a clear source of authority, correctly matched Microsoft 365 and AD users, consistent sign-in names, defined synchronization scope, an appropriate authentication method, resilient agents or staging infrastructure, monitoring and alerting, emergency access, administrative procedures, change-control documentation, and a roadmap for Conditional Access, MFA, Intune, Azure, and SaaS adoption.

This becomes the identity foundation on which the rest of the cloud strategy can be built.

The Bottom Line

For many companies, Microsoft Entra ID already exists because Microsoft 365 is already part of the business.

The missing step is connecting that cloud directory to the Active Directory environment that still controls the organization's workstations, servers, applications, and internal resources.

When implemented correctly, Active Directory and Entra ID do not compete with each other. They work together.

Active Directory continues to provide the trusted identity foundation for existing on-premises systems. Microsoft Entra ID extends those identities into Microsoft 365, Azure, SaaS applications, modern authentication, and cloud security.

Cloud adoption starts with identity. Before migrating workloads, connect the people who need to access them.

Frequently Asked Questions

How Fletcher Technology Group Can Help

Fletcher Technology Group designs and implements hybrid identity solutions that connect existing Active Directory environments to Microsoft Entra ID and Microsoft 365.

Our services include Active Directory and Entra ID readiness assessments, existing Microsoft 365 tenant reconciliation, Entra Cloud Sync and Entra Connect architecture, UPN and identity-standardization projects, Password Hash Synchronization and authentication design, Microsoft 365 identity matching, Conditional Access and multifactor authentication, Microsoft Intune and device-identity planning, Azure and SaaS single sign-on, and hybrid identity security and operational documentation.

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