[Terraform] How to config multiple ec2 private_ips in cidr_blocks of an aws_security_group resource

Let’s say we need to configure cidr_blocks of an aws_security_group resource with the private IPs of several aws EC2 instance retrieve from data resources in Terraform.

However, cidr_blocks only accept a standard CIDR format with /32 . We can accomplish it through formatlist syntax, adding a /32 string after each private_ips resources.

Example configuration:

data "aws_instances" "ec2-example" {
  filter {
    name   = "tag:Name"
    values = ["ec2-example-*"]
  }
}
resource "aws_security_group" "example" {
  vpc_id      = "vpc_example"
  name        = "example"
  description = "example"
ingress {
    protocol  = "tcp"
    from_port = 80
    to_port   = 80
cidr_blocks = ["${formatlist("%s/32", daws_instances.ec2-example.private_ips)}"]
  }
egress {
    protocol    = "-1"
    from_port   = 0
    to_port     = 0
    cidr_blocks = ["0.0.0.0/0"]
  }
tags {
    Name    = "example"
  }
}