Instance reachability check failed windows t3a instance

Hi,

This is Sean from AWS Premium Support here to help you today. I understand that after rolling back a windows update, your instance has become unreachable, and the EC2 Serial Console does not return the expected output.

I took a look at the instance, and although I can't share any account-specific information here as this is a public forum, I would like to provide the following suggestions:

1. In order to access a command line or gather meaningful data from the serial console, you must make several configurations, both at the account and instance level. Please double check that the following steps have been performed:
   a. Grant your account access to the serial console[1]
   b. enable serial console on your instance.[2]. Please note, if you have not done this step on your instance, you must apply these settings to the offline root volume of the instance, by attaching the root volume to another instance in the same AZ, and running the following commands. For this example, we will assume a secondary volume letter of E:, but make sure that you confirm the correct drive letter in your environment. Please also run all commands in CMD, not Powershell.

    bcdedit /store E:\Boot\BCD /ems {current} ON
    bcdedit /store E:\Boot\BCD /emssettings EMSPORT:1 EMSBAUDRATE:115200 
    bcdedit /store E:\Boot\BCD /set {bootmgr} displaybootmenu yes
    bcdedit /store E:\Boot\BCD /set {bootmgr} timeout 15
    bcdedit /store E:\Boot\BCD /set {bootmgr} bootems yes
   

   c. (Before proceeding with this step, consider suggestion 2 as well.) Offline the volume in disk management, and reattach it to the original instance as /dev/sda1. Start the instance and attempt to connect to SAC

2. On the offline volume of your instance, you can run EC2Rescue[3] in restore mode to perform a variety of tasks, including reverting to the Last Known Good Configuration.
   a. If this fails, you can then collect logs with EC2Rescue for further analysis. If you would like assistance reviewing these logs, this would involve sharing details that are non-public information, and would need to be sent to us through a support case with AWS using the following link[4]

Let me know if you have further findings or observations that we can assist with.

Reference:
[1] https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/configure-access-to-serial-console.html#sc-grant-account-access
[2] https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/troubleshooting-sac.html
[3] https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/ec2rw-gui.html
[4] https://console.aws.amazon.com/support/home#/case/create