Migrate AD CA: Step-by-Step Guide

Introduction
Active Directory Certificate Services (AD CS) is a critical component in enterprise environments, handling PKI (Public Key Infrastructure) tasks like issuing digital certificates for authentication, encryption, and secure communication. Migrating an AD Certificate Authority (CA) is inevitable during hardware upgrades, OS modernization, or infrastructure consolidation. But it’s not a process to take lightly—improper execution can break authentication workflows, cripple encryption, or disrupt services. This guide walks you through a bulletproof, step-by-step migration strategy, minimizing risk while ensuring continuity.

Why Migrate AD CA? Common Triggers
Before diving into the “how,” understand the “why”:

• Hardware Refresh: Legacy servers nearing end-of-life.
• Windows Server Upgrades: Migrating from Server 2012 R2/2016 to 2019/2022.
• Consolidation: Reducing CA sprawl by merging roles.
• Security Hardening: Moving to a more secure OS/build.

Prerequisites

1. Backup Existing CA: Full system state backup + CA-specific backup (certutil -backup).
2. New Server Readiness:

   • Same OS version or higher (see Microsoft’s support matrix).
   • Identical CA name, domain membership, and network configuration.
   • DNS records pre-staged (if changing hostnames, plan meticulously).

3. Permissions: Domain Admin + Enterprise Admin rights.

Step-by-Step Migration Guide

Step 1: Pre-Migration Validation

• Verify CA health:
  powershell
  certutil -viewstore -silent

• Check for unresolved revocation requests (certutil -view).
• Audit certificate templates and enrollment permissions.

Step 2: Backup the Existing CA

1. Stop the CA service:
   powershell
   Stop-Service certsvc

2. Export CA database and private key:
   powershell
   certutil -backupDB "C:\CA-Backup"
   certutil -backupkey "C:\CA-Backup"

3. Copy backups to an external drive/new server.

Step 3: Install AD CS on the Destination Server

1. Add the Active Directory Certificate Services role via Server Manager/PowerShell:
   powershell
   Install-WindowsFeature ADCS-Cert-Authority -IncludeManagementTools

2. Do not configure the CA during installation.

Step 4: Restore the CA on the New Server

1. Copy the backup files to the new server (e.g., C:\CA-Restore).

2. Run CA restoration:
   powershell
   certutil -restoreDB "C:\CA-Restore"
   certutil -restorekey "C:\CA-Restore"

3. Reconfigure the CA service using the existing key:
   powershell
   Install-AdcsCertificationAuthority -CACommonName "OldCA_Name" -Force

Step 5: Migrate Certificate Templates & Revocation Lists

• Copy templates from %windows%\NTDS\CertificateTemplates to the new server.
• CRL Migration:

  • Update CDP (CRL Distribution Points) locations if URLs change.
  • Republish CRLs via certutil -CRL.

Step 6: Decommission the Old CA (Post-Migration)

1. Disable the CA service on the old server.
2. Uninstall AD CS via Server Manager to prevent accidental reuse.
3. Update GPOs/SCCM references to point to the new CA.

Step 7: Validate the New CA

• Issue test certificates via manual/web enrollment.
• Confirm auto-enrollment works for domain-joined devices.
• Check CRL/OCSP responder accessibility externally.

Conclusion
Migrating an AD Certificate Authority demands precision—overlooking DNS dependencies, permission missteps, or template mismatches can trigger outages. By following this guide, you ensure PKI services remain uninterrupted, certificates stay trusted, and security frameworks stay intact.

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FAQs: Migrating AD CA

Q: Can I migrate from Server 2012 R2 directly to Server 2022?
A: Yes, but skip intermediate OS versions only if both source/target are supported. Always test in a lab first!

Q: Does migrating a CA invalidate existing certificates?
A: No. Certificates chain to the CA’s key, not the server. As long as the key remains intact, trust persists.

Q: How long does auto-enrollment take to switch to the new CA?
A: Domain clients refresh Group Policy every 90 mins. Force updates with gpupdate /force.

Q: What happens to revoked certificates post-migration?
A: The CRL carries over. Publish a new CRL immediately after migration to ensure revocations are current.

Q: Can I run two CAs concurrently during cutover?
A: Temporarily, yes—but ensure only one is issuing certificates for a template to avoid conflicts.

Q: Is a backup CA necessary?
A: Absolutely. Always maintain an offline root CA or a standby issuing CA for disaster recovery.

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