I’m catching up with the security group with Terraform.

When checking official DOCS, there was self referenced Security group inbound rule.

like this,

 ingress_with_self = [
    {
      from_port   = 3306
      to_port     = 3306
      protocol    = "tcp"
      description = null
    }
  ]

What happens if I attach this to an instance of rds as self – reference?

What are some examples of appropriate use?

I found this comment on reddit:

For example, an EC2 instance with that security group assigned would be able to reach another EC2 instance with that same security group.

But in my case, self-referenced inbound rule was attached on RDS(Aurora, 1 master cluster and 1 readonly instance ).

Does it allow each instance of rds to reach each other?

I searched on google but i can’t find appropriate examples