What is the reason for this issue?
The SysOps administrator does not have access to the key pair that is required for connection.
The SysOps administrator has not attached a security group to the EC2 instance to allow SSH on port 22.
The EC2 instance does not have an attached IAM role that allows Session Manager to connect to the EC2 instance.
The EC2 instance ID has not been entered into the Session Manager configuration.
Explanations:
Access to the key pair is not required for using Session Manager. Session Manager enables connections to instances without needing SSH or RDP, thus key pairs are not a factor in this context.
While security groups are important for network access, Session Manager does not require SSH access on port 22. Instead, it communicates over the AWS infrastructure, meaning the EC2 instance can be managed without SSH.
For an EC2 instance to be managed by Session Manager, it must have an IAM role that allows the necessary permissions (e.g.,ssm:Connect). Without this role, the instance cannot appear in the Session Manager list.
There is no requirement to enter the EC2 instance ID into the Session Manager configuration for it to be available for connection. As long as the instance is configured correctly with the appropriate IAM role and SSM agent, it should be listed automatically.
As I understand it, the answer is:
The EC2 instance does not have an attached IAM role that allows Session Manager to connect to the EC2 instance.