Many organizations are transitioning from traditional on-premise Active Directory setups to cloud-based solutions. In this scenario, we have:

• 25 client PCs
• Most servers already migrated to Azure VMs
• Office365 with existing AD sync
• Single Sign-On via ADFS
• Only remaining on-premise components: 2 servers handling AD and ADFS

Azure Active Directory (Azure AD) can serve as a cloud directory service, but with some important considerations:

# PowerShell check for Azure AD Connect readiness
Get-Module -Name AzureAD -ListAvailable | Select Version
Get-Module -Name MSOnline -ListAvailable | Select Version

The key technical challenge lies in local machine authentication. Traditional domain-joined computers rely on:

• Kerberos/NTLM protocols
• Local DC availability
• Group Policy processing

Azure AD supports web-based authentication flows (OAuth, SAML) but has limitations for traditional domain join.

For complete on-premise DC replacement, consider these approaches:

Option 1: Azure AD Hybrid Join

# Register device with Azure AD
dsregcmd /status
dsregcmd /join /debug

Option 2: Azure AD Domain Services

This provides managed domain controllers in Azure:

# ARM template snippet for AADDS
{
  "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "aaddsName": {
      "type": "string"
    }
  },
  "resources": [
    {
      "apiVersion": "2017-06-01",
      "type": "Microsoft.AAD/DomainServices",
      "name": "[parameters('aaddsName')]",
      "location": "[resourceGroup().location]"
    }
  ]
}

A recommended migration path:

1. Prepare Azure AD Connect with writeback enabled
2. Implement Azure AD Device Registration
3. Configure Conditional Access policies
4. Test authentication flows
5. Gradually decommission on-premise DCs

Before final migration, verify:

When migrating infrastructure to Azure, many organizations hit a critical architectural decision point: can Azure Active Directory (Azure AD) fully replace traditional on-premise Active Directory Domain Services (AD DS)? Based on multiple production deployments, here's what you need to know.

Azure AD isn't just "Active Directory in the cloud" - it's a fundamentally different service:

• Authentication Protocols: Azure AD uses modern protocols (OAuth 2.0, SAML) vs AD DS's Kerberos/NTLM
• Device Management: Traditional Group Policy Objects (GPOs) aren't natively supported
• Network Services: DNS, DHCP, and other network services typically handled by DCs aren't included

For most enterprises, we recommend a phased approach using Azure AD Connect sync:

# Sample Azure AD Connect configuration for staged migration
Set-ADSyncAADCompanyFeature -Force
-EnablePasswordHashSync $true
-EnableDeviceWriteback $true
-EnableGroupWriteback $true

Modern Windows devices can authenticate directly to Azure AD using Workplace Join:

1. Device registers with Azure AD during OOBE or via Settings
2. Authentication tokens are cached for offline access
3. Conditional Access policies enforce security requirements

For apps requiring traditional AD authentication, consider these options:

// C# example for handling both Azure AD and AD FS tokens
var authContext = new AuthenticationContext(authority);
var result = await authContext.AcquireTokenAsync(resource, credential);
if (result.AccessTokenType == "urn:ietf:params:oauth:token-type:jwt") {
    // Azure AD token
} else {
    // Fallback to AD FS handling
}

• Audit all domain-joined devices and applications
• Implement Azure AD Premium P1/P2 for advanced features
• Configure Azure AD Connect with password writeback
• Test conditional access policies before cutover