Troubleshoot Amazon EC2 Windows instance start issues

To enable DHCP on a Windows instance that you can't connect to

1. Stop the affected instance and detach its root volume.

2. Launch a temporary instance in the same Availability Zone as the affected instance.

   Warning

   If your temporary instance is based on the same AMI that the original instance is based on, you must complete additional steps or you won't be able to boot the original instance after you restore its root volume because of a disk signature collision. Alternatively, select a different AMI for the temporary instance. For example, if the original instance uses the AWS Windows AMI for Windows Server 2016, launch the temporary instance using the AWS Windows AMI for Windows Server 2019.

3. Attach the root volume from the affected instance to this temporary instance. Connect to the temporary instance, open the Disk Management utility, and bring the drive online.

4. From the temporary instance, open Regedit and select HKEY_LOCAL_MACHINE. From the File menu, choose Load Hive. Select the drive, open the file Windows\System32\config\SYSTEM, and specify a key name when prompted (you can use any name).

5. Select the key that you just loaded and navigate to ControlSet001\Services\Tcpip\Parameters\Interfaces. Each network interface is listed by a GUID. Select the correct network interface. If DHCP is disabled and a static IP address assigned, EnableDHCP is set to 0. To enable DHCP, set EnableDHCP to 1, and delete the following keys if they exist: NameServer, SubnetMask, IPAddress, and DefaultGateway. Select the key again, and from the File menu, choose Unload Hive.

   Note

   If you have multiple network interfaces, you'll need to identify the correct interface to enable DHCP. To identify the correct network interface, review the following key values NameServer, SubnetMask, IPAddress, and DefaultGateway. These values display the static configuration of the previous instance.

6. (Optional) If DHCP is already enabled, it's possible that you don't have a route to the metadata service. Updating EC2Config can resolve this issue.

   1. Download and install the latest version of the EC2Config service. For more information about installing this service, see Install the latest version of EC2Config.

   2. Extract the files from the .zip file to the Temp directory on the drive you attached.

   3. Open Regedit and select HKEY_LOCAL_MACHINE. From the File menu, choose Load Hive. Select the drive, open the file Windows\System32\config\SOFTWARE, and specify a key name when prompted (you can use any name).

   4. Select the key that you just loaded and navigate to Microsoft\Windows\CurrentVersion. Select the RunOnce key. (If this key doesn't exist, right-click CurrentVersion, point to New, select Key, and name the key RunOnce.) Right-click, point to New, and select String Value. Enter Ec2Install as the name and C:\Temp\Ec2Install.exe -q as the data.

   5. Select the key again, and from the File menu, choose Unload Hive.

7. (Optional) If your temporary instance is based on the same AMI that the original instance is based on, you must complete the following steps or you won't be able to boot the original instance after you restore its root volume because of a disk signature collision.

   Warning

   The following procedure describes how to edit the Windows Registry using Registry Editor. If you are not familiar with the Windows Registry or how to safely make changes using Registry Editor, see Configure the Registry.

   1. Open a command prompt, type regedit.exe, and press Enter.

   2. In the Registry Editor, choose HKEY_LOCAL_MACHINE from the context menu (right-click), and then choose Find.

   3. Type Windows Boot Manager and then choose Find Next.

   4. Choose the key named 11000001. This key is a sibling of the key you found in the previous step.

   5. In the right pane, choose Element and then choose Modify from the context menu (right-click).

   6. Locate the four-byte disk signature at offset 0x38 in the data. Reverse the bytes to create the disk signature, and write it down. For example, the disk signature represented by the following data is E9EB3AA5:

      ...
      0030  00 00 00 00 01 00 00 00
      0038  A5 3A EB E9 00 00 00 00
      0040  00 00 00 00 00 00 00 00
      ...

   7. In a Command Prompt window, run the following command to start Microsoft DiskPart.

      diskpart

   8. Run the following DiskPart command to select the volume. (You can verify that the disk number is 1 using the Disk Management utility.)

      DISKPART> select disk 1
      
      Disk 1 is now the selected disk.

   9. Run the following DiskPart command to get the disk signature.

      DISKPART>  uniqueid disk
      
      Disk ID: 0C764FA8

   10. If the disk signature shown in the previous step doesn't match the disk signature from BCD that you wrote down earlier, use the following DiskPart command to change the disk signature so that it matches:

       DISKPART> uniqueid disk id=E9EB3AA5

8. Using the Disk Management utility, bring the drive offline.

   Note

   The drive is automatically offline if the temporary instance is running the same operating system as the affected instance, so you won't need to bring it offline manually.

9. Detach the volume from the temporary instance. You can terminate the temporary instance if you have no further use for it.

10. Restore the root volume of the affected instance by attaching the volume as /dev/sda1.

11. Start the affected instance.