Creating Security Group with CIDR Block with /32

[Cyber Corp]

Hello

I have two terraform resource: AWS EIP and AWS Security Group. I want that EIP should automatically be whitelisted in the security group.

Since I am using the 0.12 version of Terraform, I thought to avoid using ${..} approach and tried referencing follow in cidr_block with the latest configuration language, however, the following block gives an error:

Error: Invalid operand

  on reference.tf line 19, in resource "aws_security_group" "mysg":

  19:    cidr_blocks = [aws_eip.lb.public_ip/32]

    |----------------

    | aws_eip.lb.public_ip is "52.88.235.110"

Unsuitable value for left operand: a number is required.

resource "aws_eip" "lb" {
  vpc      = true
}


resource "aws_security_group" "mysg" {
   name = "terraform-sg"


   ingress {
   from_port   = 443
   to_port     = 443
   protocol    = "tcp"
   cidr_blocks = [aws_eip.lb.public_ip/32]

  }


}

When I specify ["${aws_eip.lb.public_ip}/32"], it works perfectly but I want to know is using ${..} the right approach even with 0.12?

[Andrew Jeffree]

Using “${}” is correct in this case as you’re making it a string when you add the ‘/32’. Doing it the initial way you tried initially has it trying to treat it as a math operation at a guess.

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[⁞ Fernando Miguel]

You are interpolating a var and a string. 

So you still need to do it with ${} 

--
Fernando Miguel