My EC2 is terminated after I attach it to auto scaling

Hello.

AutoScaling automatically deletes EC2s that are determined to have problems through health checks and launches new EC2s.
EC2 that is launched in an AutoScaling group is created based on the AMI set in the launch template, so it must contain some kind of OS.
First of all, I think it's a good idea to start EC2 from the launch template and troubleshoot.

Check out the documentation below for other troubleshooting methods.
https://docs.aws.amazon.com/autoscaling/ec2/userguide/ts-as-instancelaunchfailure.html