Introduction to Terraform

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Terraform allows you to manage your AWS, and other cloud infrastructure, the same way you would manage servers using configuration management products like CFEngine or Puppet. Terraform is idempotent and convergent so only required changes are applied.

I whipped up this example to build:

  1. An SSH public key to be installed on the created EC2 instance.
  2. A security group allowing HTTP and HTTPS.
  3. A security group allowing SSH.
  4. A tc2.micro EC2 instance with the above applied to it.

The 'provider' part of the file indicates to terraform to use its AWS provider with the given credentials. If you know AWS at all the terraform code is not hard to follow.

Create a file in your current directory called demo.tf. When you run terrafrom it searches the current directory for .tf files and reads them according to your instructions. For example:

  • Terraform plan will report what must be done, but perform no changes.
  • Terraform apply will make the changes shown above.
  • Terraform show will show the current state.
  • Terraform destroy will destroy everything that is defined.

Note that there seems to be a built in order in which terraform runs that is not related to the order of the file. This is much like normal ordering in CFEngine. For example, when I run this code with nothing configured in AWS, it will try to build the server instance first, but fails because the groups and keys are not yet defined. But the groups and keys will be created next, so, run terraform a second time and it will converge, by creating just the instance while leaving the already existing groups and keys as they are.


provider "aws" {
   access_key = "your_key_here"
   secret_key = "your_secret_here"
   region = "us-east-1"
}

resource "aws_key_pair" "neptune" {
   key_name = "neptune"
   public_key = "ssh-rsa AAA removed for brevity 1XCr neil@neptune"
}

resource "aws_security_group" "ssh" {
   name = "ssh"
   description = "Allow inbound ssh"
   ingress = {
      from_port = 0
      to_port   = 22
      protocol  = "tcp"
      cidr_blocks = [ "0.0.0.0/0" ]
   }
}

resource "aws_security_group" "http" {
   name = "http"
   description = "Allow inbound http"
   ingress = {
      from_port = 0
      to_port   = 80 
      protocol  = "tcp"
      cidr_blocks = [ "0.0.0.0/0" ]
   }
   egress = {
      from_port = 0
      to_port   = 80
      protocol  = "tcp"
      cidr_blocks = [ "0.0.0.0/0" ]
   }
   egress = {
      from_port = 0
      to_port   = 443
      protocol  = "tcp"
      cidr_blocks = [ "0.0.0.0/0" ]
   }
}

resource "aws_instance" "tfdemo" {

    ami = "ami-60b6c60a"
    instance_type = "t2.micro"

   key_name = "neptune"
   security_groups = [ "ssh", "http", "default" ]
}

I've shown only a small portion of what terraform can do. Most things you might want to do in AWS can be defined in Terraform and not just AWS. Terraform also supports Cloudflare, DigitalOcean, Docker, Google Cloud, vSphere, Azure, and more.

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