Lost security group on running instance

Question

Hello, there are two running EC2 instances (launched in 2019) in my account, and the security groups for these instances have been lost. 
When I select the instance and go to the security tab, I see the message 'Failed to describe security groups. The security group 'sg-a95225a8' does not exist.'
Currently, there is only one security group named 'default' in the security group list.

I believe the security group associated with the instance is protected from deletion, but it has disappeared.
I have checked the security group list in the same region as the instance.

Although I cannot see the security group rule, the instance is still working under the lost security group, as my SSH port is still permitted as usual. 
How can I find my lost security group? Please help.

I am not sure if it will be helpful, but the instance IDs are i-272d2324 and i-22ced23b.

Thanks a lot.

Answer

Hi, I contacted one of our SME in AWS and he told that the old and deprecated EC2-classic security groups are still there, but not visible anymore. He suggested to open a ticket to solve the issue of having them listed out by their support group, so that you can migrate them and then ask to remove the old one.

Answer

In the blog I included in the previous mail, you can find the link to the https://github.com/aws-samples/ec2-classic-resource-finder that can help you find the security groups EC2-Classic

Answer

So, I'm understanding that you had EC2-Classic Security Group and now you need to migrate to EC2-VPC due to EC2-Classic sunset. This is a good starting point to find classic resources and migrate to the EC2-VPC model. https://aws.amazon.com/blogs/aws/ec2-classic-is-retiring-heres-how-to-prepare/
Please advise how you are moving forward and if needs other help

Answer

Hi, did you check in trail to understand if anyone did anything? Do you have full access and no policy restriction on NSGs? Is the NSG in the default VPC?
Try also aws ec2 describe-security-groups --filters Name=vpc-id,Values=vpc-XXX --filters Name=group-name,Values=your_group_name
Same result?

Answer

Did you check via aws ec2-describe-security-groups -- to verify if still present the original security group in the list?
Did you check using aws ec2 describe-instances --instance-ids  --query with the network-interface.group-id parameter to check what you see via cli and not console?

Lost security group on running instance

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