"" is not a valid CIDR block: invalid CIDR address

Question

I have a VPC defined in terraform:

//vpc.tf
resource "aws_vpc" "my_vpc" {
  cidr_block = "10.0.0.0/16"
}

And I am trying to create a security group:

// securityGroup.tf
resource "aws_security_group" "allow_tls" {
  name        = "allow_tls"
  description = "Allow TLS inbound traffic"
  vpc_id      = aws_vpc.my_vpc.id
  ingress {
    description      = "TLS from VPC"
    from_port        = 443
    to_port          = 443
    protocol         = "tcp"
    cidr_blocks      = [aws_vpc.my_vpc.cidr_block]
    ipv6_cidr_blocks = [aws_vpc.my_vpc.ipv6_cidr_block]
  }
  egress {
    from_port        = 0
    to_port          = 0
    protocol         = "-1"
    cidr_blocks      = ["0.0.0.0/0"]
    ipv6_cidr_blocks = ["::/0"]
  }
}

However, when I run terraform plan I get the error Error: "" is not a valid CIDR block: invalid CIDR address:

I thought that the cidr_block defined in my vpc would be available to the securityGroup, but that seems to not be the case. How do I correctly reference the cidr_block from my vpc?

Full error output:

│ Error: "" is not a valid CIDR block: invalid CIDR address: 
│ 
│   with module.shared.aws_security_group.allow_tls,
│   on modules/shared/securityGroup.tf line 1, in resource "aws_security_group" "allow_tls":
│    1: resource "aws_security_group" "allow_tls" {

Answer 1

You haven't configured your VPC with any IPV6 addresses. So this line in your security group should be deleted:

ipv6_cidr_blocks = [aws_vpc.my_vpc.ipv6_cidr_block]