How to join ec2 instance to local MS Active Directory manually without AWS Directory services

Since the instance reachability fails and the system log is blank, it suggests a potential driver or network configuration issue during the boot process. Verify that the ENI (Elastic Network Interface) is correctly associated with the instance after reboot and that the security group allows necessary traffic. Check if there are any specific updates or patches for the Windows Server 2025 AMI, as this might be a bug. Consider testing a custom AMI built from a functioning instance or use a different 2025 AMI version if available.

I tested around this issue, and I have changed the machine type:

• It does not work with t3.medium.
• c6a.2xlarge works.

Greeting

Hi Joachim,

Thank you for your detailed explanation of the issue! It sounds like you've successfully joined EC2 instances running Microsoft Windows Server 2025 to your local Active Directory (AD) via a VPN connection, but you're encountering a frustrating issue with instance inaccessibility after a reboot. Let’s break this down and address it step by step.

Clarifying the Issue

You're leveraging a VPN to connect your AWS private subnet to your on-premises network and using your local DNS server to successfully integrate EC2 instances into your local Active Directory. This has worked well for instances running Windows Server 2022, but with Windows Server 2025, the instances become inaccessible after a reboot, failing the "Instance reachability check." Even the system logs in the AWS Console are blank, making troubleshooting challenging.

This issue likely stems from compatibility or configuration changes introduced in Windows Server 2025. Possible culprits include differences in driver support, network configuration persistence, or system startup settings. By addressing these potential areas of conflict, we’ll aim to resolve the inaccessibility and ensure seamless domain integration.

Why This Matters

Joining EC2 instances to an on-premises AD is a critical use case for hybrid cloud environments, allowing seamless integration between AWS and local resources. This functionality supports essential operations like centralized authentication, policy management, and resource sharing.

In this specific case, resolving the issue ensures compatibility with the latest Windows Server versions, reducing risks of downtime, improving operational efficiency, and enabling scalability for future upgrades. Additionally, addressing the inaccessibility safeguards against longer troubleshooting cycles and potential workflow disruptions.

Key Terms

• AWS EC2: Elastic Compute Cloud instances used for running virtual servers in the AWS cloud.
• Active Directory (AD): Microsoft’s directory service for managing domain networks, including authentication and authorization.
• DNS: Domain Name System used to resolve domain names into IP addresses, critical for AD operations.
• Instance Reachability Check: An AWS health check that verifies the network and system-level accessibility of an EC2 instance.
• Serial Console Access: A feature that allows debugging and troubleshooting of instances that are inaccessible via standard methods.

The Solution (Our Recipe)

Steps at a Glance:

1. Verify DNS configuration and reachability between the EC2 instance and local AD.
2. Update or verify drivers for compatibility with Windows Server 2025.
3. Disable fast startup or features that may interfere with boot processes.
4. Check and reapply network settings, including static routes.
5. Test rejoining the instance to the domain.
6. Enable serial console access for deeper troubleshooting if the instance remains inaccessible.

Step-by-Step Guide:

1. Verify DNS Configuration and Reachability
   • Ensure that the local DNS server IP is correctly set in the EC2 instance's network settings.
   • Use PowerShell to verify connectivity:

     Test-Connection -ComputerName <local-DNS-IP>

     Replace <local-DNS-IP> with the actual IP address of your DNS server.
   • Confirm that DNS persists after reboot:

     Get-DnsClientServerAddress -InterfaceAlias "Ethernet"

2. Update or Verify Drivers for Compatibility
   • Confirm that Windows Server 2025 on the default AMI is fully up to date. Use Windows Update to apply any missing patches.
   • If the AMI includes custom drivers, verify they are compatible with Windows Server 2025 by consulting the AWS documentation or installing generic versions if applicable.

3. Disable Fast Startup and Related Features
   • Open Power Options > Choose what the power buttons do > Change settings that are currently unavailable.
   • Disable Turn on fast startup and reboot the instance.

4. Reapply Network Settings
   • Reconfirm the static routes for the VPN connection and ensure the DNS IP persists across reboots.
   • To set a static DNS server:

     Set-DnsClientServerAddress -InterfaceAlias "Ethernet" -ServerAddresses "<local-DNS-IP>"

   • Replace <local-DNS-IP> with the appropriate DNS server address.

5. Rejoin the Domain
   • Leave and rejoin the domain to ensure the computer account is registered correctly.

     Remove-Computer -UnjoinDomaincredential <DomainAdmin> -Force -Restart
     Add-Computer -DomainName "<DomainName>" -Credential <DomainAdmin>
     Restart-Computer

     Replace <DomainAdmin> and <DomainName> with appropriate values.

6. Enable Serial Console Access for Deeper Troubleshooting
   • Use the AWS Management Console to enable serial console access for the instance.
   • Connect via the serial console to check logs and configuration issues that may be causing the reboot failure.
   • Refer to AWS Serial Console Access Guide for detailed instructions.

Closing Thoughts

The issue appears to be tied to Windows Server 2025's configuration or compatibility with the AWS infrastructure. By verifying DNS, updating drivers, and disabling potentially conflicting features, you should be able to resolve the inaccessibility after reboot. Testing with serial console access provides a fallback option for advanced troubleshooting.

If these steps don’t fully resolve the issue, consider testing with a different EC2 instance type or using a Windows Server 2022 AMI to isolate whether the problem lies specifically with the Server 2025 AMI. Exploring AWS forums or reaching out to AWS Support may also provide additional insights.

Here are some relevant documentation links to guide you further:

• AWS EC2 Instance Troubleshooting
• Microsoft Active Directory Documentation
• AWS Hybrid Connectivity Overview
• AWS EC2 Windows AMI Release Notes
• AWS Serial Console Access Guide

Farewell

Joachim, it’s clear you’re navigating a complex setup with great skill. I’m confident these steps will get you closer to a solution. Let me know how it goes—I’m here to help if anything else comes up! 😊🚀

Cheers,

Aaron 😊

Hi Joachim,

Thank you for sharing your solution—it’s fantastic to see that switching the instance type resolved the issue! Your observation that the problem occurs with t3.medium but not with c6a.2xlarge provides critical insight. Based on this, it seems likely that the issue may stem from the following factors:

1. Resource Allocation

The t3.medium instance type has limited CPU and memory resources compared to the c6a.2xlarge. Windows Server 2025, especially when configured to join a domain and handle startup tasks like applying group policies or synchronizing with a local AD, might exceed the resource capabilities of the smaller instance, leading to boot or reachability failures.

2. Hypervisor Compatibility

The T3 instance family uses the AWS Nitro hypervisor, which might not fully align with the requirements of the Windows Server 2025 AMI in this particular scenario. The C6a family, being part of the newer generation with higher-performance AMD processors, might better accommodate the OS's needs.

3. Driver or Hardware Optimization

Drivers or configurations within the Windows Server 2025 AMI may be optimized for newer or more powerful instance families like C6a. This could explain the discrepancy in behavior between the two instance types.

Suggestions for Further Exploration

If you’re interested in running this setup on a T3 instance for cost efficiency, consider the following:

1. Check for Updates: Ensure the Windows Server 2025 AMI is fully updated with the latest patches and drivers. Microsoft and AWS may release updates that address these compatibility issues.

2. Test with Other Instance Types: Try other sizes within the T3 family, such as t3.large, to determine if a slight increase in resources resolves the problem.

3. Monitor Boot Behavior: Use the serial console or enable enhanced logging on the instance to capture boot-time errors. This can provide further clues about why the t3.medium instance is failing.

4. Document Resource Usage: Use tools like CloudWatch to monitor resource usage on t3.medium during domain join and startup to identify bottlenecks or resource contention.

Acknowledgment

Your persistence and detailed troubleshooting have been instrumental in identifying this issue—well done! Sharing this information will undoubtedly help others navigating similar setups.

Let me know if you’d like additional guidance or have more findings to share. 😊🚀

Best regards,
Aaron 😊