🧼Terraform Resources

Terraform uses resource blocks to manage infrastructure, such as virtual networks, compute instances, or higher-level components such as DNS records. Resource blocks represent one or more infrastructure objects in your Terraform configuration.

Most Terraform providers have a number of different resources that map to the appropriate APIs to manage that particular infrastructure type.

Generic	AWS Provider Resource	AWS Infrastructure
Resource A	aws_instance	EC2 Instance
Resource B	aws_security_group	Security Group

In this tutorial, you will create an EC2 instance that runs a PHP web application. You will then refer to documentation in the Terraform Registry to create a security group to make the application publicly accessible.

Review the random_pet resource

The first resource block defines a random_pet resource named name, which generates a random pet name. You can use the name generated by this resource to ensure that your other resources have unique names.

resource "random_pet" "name" {}

Resource blocks declare a resource type and name. Together, the type and name form a resource identifier (ID) in the format resource_type.resource_name, in this case random_pet.name. The resource's ID must be unique within a workspace. When Terraform displays information about this resource in its output it will use the resource ID.

Resource types always start with the provider name followed by an underscore. The random_pet resource type belongs to the random provider.

The Terraform Registry houses the documentation for Terraform providers and their associated resources. Open the random_pet documentation page and notice that it is nested under the documentation for the random provider. The page contains a description of the random_pet resource, an example usage, argument reference, and attribute reference.

Resources have arguments, attributes, and meta-arguments.

• Arguments configure a particular resource; because of this, many arguments are resource-specific. Arguments can be required or optional, as specified by the provider. If you do not supply a required argument, Terraform will give an error and not apply the configuration.

• Attributes are values exposed by an existing resource. References to resource attributes take the format resource_type.resource_name.attribute_name. Unlike arguments which specify an infrastructure object's configuration, a resource's attributes are often assigned to it by the underlying cloud provider or API.

• Meta-arguments change a resource's behavior, such as using a count meta-argument to create multiple resources. Meta-arguments are a function of Terraform itself and are not resource or provider-specific.

The random_pet resource has four optional arguments and exposes one attribute. Because there are no required arguments, you can define the random_pet.name resource without arguments.

Apply your configuration to create the two resources. Confirm the operation with a yes.

$ terraform apply
## ...

Plan: 2 to add, 0 to change, 0 to destroy.
## ...

Apply complete! Resources: 2 added, 0 changed, 0 destroyed.

Outputs:

application-url = "ec2-18-236-123-132.us-west-2.compute.amazonaws.com/index.php"
domain-name = "ec2-18-236-123-132.us-west-2.compute.amazonaws.com"

The domain-name output will display your EC2 instance's endpoint upon completion. However, if you try to visit the URL, it will not resolve. This is because you have not yet configured access to port 80 of the instance.

If you use Terraform Cloud to provision your resources, your workspace now displays the list of all of the resources it manages and the outputs for your configuration.

Associate security group with instance

To enable access to the EC2 instance's web server, you must define a security group that allows ingress traffic on port 80 and all egress traffic, and associate the security group with your instance.

Review the configuration options available on the aws_security_group documentation page. Then, define a new aws_security_group resource named web-sg in main.tf that allows ingress traffic on port 80 and all egress traffic for all CIDR blocks.

Your security group resource should be similar to the following:

resource "aws_security_group" "web-sg" {
  name = "${random_pet.name.id}-sg"
  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

Then, update your aws_instance.web resource to use this security group. As specified in the aws_instance Argument Reference section, thevpc_security_group_ids argument requires a list of security group IDs.

Add the vpc_security_group_ids argument to the aws_instance.web resource as a list by placing the aws_security_group.web-sg.id attribute inside square brackets.

resource "aws_instance" "web" {
  ami                    = "ami-a0cfeed8"
  instance_type          = "t2.micro"
  user_data              = file("init-script.sh")
+ vpc_security_group_ids = [aws_security_group.web-sg.id]

  tags = {
    Name = random_pet.name.id
  }
}

Clean up your infrastructure

Now that you have verified that the EC2 instance is publicly available, run terraform destroy to destroy the resources. Remember to respond to the confirmation prompt with yes.