amazon web services - Using data for existing resource (security group), getting: A managed resource has not been declared in the root module

Question

Learning Terraform, I'm trying to bring up an EC2 instance, reusing existing security group (tagged my-tib-sg).

I'm getting the following error, and not sure what I'm doing wrong:

Error: Reference to undeclared resource

on module_three.tf line 62, in resource "aws_instance" "nginx":
62:   vpc_security_group_ids = [aws_security_groups.my-tib-sg.id]

A managed resource "aws_security_groups" "my-tib-sg" has not been declared in
the root module.

Here is the code:

##################################################################################
# VARIABLES
##################################################################################

variable "aws_access_key" {}
variable "aws_secret_key" {}
variable "private_key_path" {}
variable "key_name" {}
variable "region" {
  default = "us-east-1"
}

##################################################################################
# PROVIDERS
##################################################################################

provider "aws" {
  access_key = var.aws_access_key
  secret_key = var.aws_secret_key
  region     = var.region
}

##################################################################################
# DATA
##################################################################################

data "aws_ami" "aws-linux" {
  most_recent = true
  owners      = ["amazon"]

  filter {
    name   = "name"
    values = ["amzn-ami-hvm*"]
  }

  filter {
    name   = "root-device-type"
    values = ["ebs"]
  }

  filter {
    name   = "virtualization-type"
    values = ["hvm"]
  }
}

data "aws_security_groups" "my-tib-sg" {
  tags = {
    Name = "my-tib-sg"
  }
}


##################################################################################
# RESOURCES
##################################################################################

resource "aws_instance" "nginx" {
  ami                    = data.aws_ami.aws-linux.id
  instance_type          = "t2.micro"
  key_name               = var.key_name
  vpc_security_group_ids = [aws_security_groups.my-tib-sg.id]

  connection {
    type        = "ssh"
    host        = self.public_ip
    user        = "ec2-user"
    private_key = file(var.private_key_path)

  }

  provisioner "remote-exec" {
    inline = [
      "sudo yum install nginx -y",
      "sudo service nginx start"
    ]
  }
}

##################################################################################
# OUTPUT
##################################################################################

output "aws_instance_public_dns" {
  value = aws_instance.nginx.public_dns
}

question from:https://stackoverflow.com/questions/65831149/using-data-for-existing-resource-security-group-getting-a-managed-resource-h

Answer 1

When referring to data sources you need to prefix the address with data. to differentiate between data sources and resources.

So in your case you should use data.aws_security_groups.my-tib-sg.id like so:

##################################################################################
# VARIABLES
##################################################################################

variable "aws_access_key" {}
variable "aws_secret_key" {}
variable "private_key_path" {}
variable "key_name" {}
variable "region" {
  default = "us-east-1"
}

##################################################################################
# PROVIDERS
##################################################################################

provider "aws" {
  access_key = var.aws_access_key
  secret_key = var.aws_secret_key
  region     = var.region
}

##################################################################################
# DATA
##################################################################################

data "aws_ami" "aws-linux" {
  most_recent = true
  owners      = ["amazon"]

  filter {
    name   = "name"
    values = ["amzn-ami-hvm*"]
  }

  filter {
    name   = "root-device-type"
    values = ["ebs"]
  }

  filter {
    name   = "virtualization-type"
    values = ["hvm"]
  }
}

data "aws_security_groups" "my-tib-sg" {
  tags = {
    Name = "my-tib-sg"
  }
}


##################################################################################
# RESOURCES
##################################################################################

resource "aws_instance" "nginx" {
  ami                    = data.aws_ami.aws-linux.id
  instance_type          = "t2.micro"
  key_name               = var.key_name
  vpc_security_group_ids = [data.aws_security_groups.my-tib-sg.id]

  connection {
    type        = "ssh"
    host        = self.public_ip
    user        = "ec2-user"
    private_key = file(var.private_key_path)

  }

  provisioner "remote-exec" {
    inline = [
      "sudo yum install nginx -y",
      "sudo service nginx start"
    ]
  }
}