Tutorial 02 | Terraform – toicodemoingay

01

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Introduction

In the previous post, we talked about what Infrastructure as Code is and why we should use Terraform, and we also made the first simple example of Terraform. In this lecture, we will learn in more detail how to initialize the project directory and write configuration files for Terraform.

Continuing the simple example, we will create an EC2 on AWS Cloud. To create a new Infrastructure, we will follow the following steps:

1. Create a Workspace

2. Write a configuration file

3. Initialize Workspace with the terraform init command

4. Check the generated resource with the terraform plan command

5. Create the resource with the terraform apply command

02

of 07

Create a Workspace and write a configuration

First, we will create a Workspace. Create a folder. Create a directory called ec2. Then we make a file named main.tf (you can name it whatever) in the directory. Paste the following code:

provider "aws" {
  region  = "us-west-2"
}
resource "aws_instance" "app_server" {
  ami           = "ami-08d70e59c07c61a3a"
  instance_type = "t2.micro"
  tags = {
    Name = "EC2Demo"
  }
}

Next, we run the terraform init command and let it download the aws provider to the current directory so that Terraform can use these Providers and call the API to AWS to create resources for us. About the syntax and meaning of the syntax in the above Terraform configuration, you can see in the previous post.

03

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Initialize Workspace

terraform init

Initializing the backend...

Initializing provider plugins...
- Finding hashicorp/aws versions matching "~> 4.16"...
- Installing hashicorp/aws v4.17.0...
- Installed hashicorp/aws v4.17.0 (signed by HashiCorp)

Terraform has created a lock file .terraform.lock.hcl to record the provider
selections it made above. Include this file in your version control repository
so that Terraform can guarantee to make the same selections by default when
you run "terraform init" in the future.

Terraform has been successfully initialized!

You may now begin working with Terraform. Try running "terraform plan" to see
any changes that are required for your infrastructure. All Terraform commands
should now work.

If you ever set or change modules or backend configuration for Terraform,
rerun this command to reinitialize your working directory. If you forget, other
commands will detect it and remind you to do so if necessary.

After you run the init command, you will see a folder named .terraform created, which contains the Provider code. The directory structure after we run the init statement.

├── .terraform
│   └── providers
│       └── registry.terraform.io
│           └── hashicorp
│               └── aws
│                   └── 3.68.0
│                       └── linux_amd64
│                           └── terraform-provider-aws_v3.68.0_x5
├── .terraform.lock.hcl
└── main.tf

04

of 07

Check the resource

After initializing the Workspace, we need to see what resources will be created before we create one. This step is optional. We just run through this step to check what the resource will look like before we build it on our existing infrastructure. To check the resource, we run the command terraform plan.

terraform plan

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the
following symbols:
  + create

Terraform will perform the following actions:

  # aws_instance.hello will be created
  + resource "aws_instance" "hello" {
      + ami                                  = "ami-08d70e59c07c61a3a"
      + arn                                  = (known after apply)
      ...
    }

Plan: 1 to add, 0 to change, 0 to destroy.

───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

Note: You didn't use the -out option to save this plan, so Terraform can't guarantee to take exactly these actions if you
run "terraform apply" now.

When you run the plan command, Terraform will show you what resources will be created. In the line displayed near the bottom, you will see Plan: 1 to add, 0 to change, 0 to destroy., meaning there will be 1 resource added to our existing infrastructure.

In addition to displaying the created resources, this command will also check the syntax error of the Terraform configuration file. It will report an error if the syntax is not correct.

When there are too many resources and the plan command is slow, you can speed it up by adding the -parallelism=n attribute. The example is as follows: terraform plan -parallelism=2

If you need to save the output of the plan command, you can use the -out attribute at runtime. For example, we will keep the result of the plan command in a JSON file.

terraform plan -out plan.out

terraform show -json plan.out > plan.json

05

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Create resources

After we finish the checking, we need to run the following command to create the resource.

terraform apply

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the
following symbols:
  + create

Terraform will perform the following actions:

  # aws_instance.app_server will be created
  + resource "aws_instance" "app_server" {
      + ami                                  = "ami-08d70e59c07c61a3a"
      + arn                                  = (known after apply)
      ...
    }

Plan: 1 to add, 0 to change, 0 to destroy.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value:

When we run the apply command, Terraform will rerun the plan command first, previewing the resources and showing a place to ask us if we want to create these resources. If so, enter ‘yes’ only if you still wish to create the resource.

As we can see, the apply command also runs the plan command, then why do we need to run the plan command earlier? The above commands are designed for the CI/CD process. We can run the plan command first, with the -out attribute to preview the resource. Then we will run the apply command with the results of the previous plan command.

The first is to run the command to check the resource.

terraform plan -out plan.out

If everything is ok, the above command will succeed, and next, we will run the command to create the resource.

terraform apply "plan.out"

Ok, back to the apply command above, enter yes so that it creates EC2 on AWS for us.

...
Plan: 1 to add, 0 to change, 0 to destroy.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

aws_instance.hello: Creating...
aws_instance.hello: Still creating... [10s elapsed]
aws_instance.hello: Still creating... [20s elapsed]
aws_instance.hello: Still creating... [30s elapsed]
aws_instance.hello: Still creating... [40s elapsed]
aws_instance.hello: Creation complete after 42s [id=i-0c0285db1ffe968a2]

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

When the creation is complete, you’ll see a new file called terraform.tfstate.

.
├── .terraform
│   └── providers
│       └── registry.terraform.io
│           └── hashicorp
│               └── aws
│                   └── 3.68.0
│                       └── linux_amd64
│                           └── terraform-provider-aws_v3.68.0_x5
├── .terraform.lock.hcl
├── main.tf
└── terraform.tfstate

Terraform uses this file for managing and tracking all resources on the infrastructure. Click on it, and you will see all the EC2 attributes.

{
  "version": 4,
  "terraform_version": "1.0.0",
  "serial": 1,
  "lineage": "fa28c290-92d6-987f-c49d-bc546b296c2b",
  "outputs": {},
  "resources": [
    {
      "mode": "managed",
      "type": "aws_instance",
      "name": "app_server",
      "provider": "provider["registry.terraform.io/hashicorp/aws"]",
      "instances": [
        {
          "schema_version": 1,
          "attributes": {
            "ami": "ami-08d70e59c07c61a3a",
            ...
}

We have completed creating EC2 on AWS. To delete a resource, you run the terraform destroy command. When you run it, it will run the plan command first to list the resources it will delete and ask if you want to execute the deletion. Enter yes, and Terraform will delete EC2 for you. After the deletion is successful, you open the terraform.tfstate and see that the resources field in this file will be empty.

{
  "version": 4,
  "terraform_version": "1.0.0",
  "serial": 3,
  "lineage": "fa28c290-92d6-987f-c49d-bc546b296c2b",
  "outputs": {},
  "resources": []
}

Above are the steps we need to take to create a new infrastructure. Besides, we use resource blocks to build infrastructure. Terraform also provides us another block to query and search for data on AWS. This block will help us create infrastructure more flexibly instead of having to fill the value of resources hard. For example, in the ami field of EC2, we leave the value as ami-08d70e59c07c61a3a. To know this value, we have to go to AWS to find it. However, other people also need to know what kind of AMI we use for our EC2 instance.

06

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Data block

Terraform provides us with a block named data. This block will not perform resource creation on the infrastructure. We can use this data block to call the API to the infrastructure through our Provider and get information about a particular resource. We update the main.tf file as follows:

provider "aws" {
  region = "us-west-2"
}
data "aws_ami" "ubuntu" {
  most_recent = true
  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"]
  }
  owners = ["099720109477"] # Canonical Ubuntu AWS account id
}
resource "aws_instance" "app_server" {
  ami           = data.aws_ami.ubuntu.id
  instance_type = "t2.micro"
  tags = {
    Name = "EC2Demo"
  }
}

When you run the plan command, you will see in the Plan line near the bottom it still shows only 1 resource that will be added because the data block does not create a resource. Moreover, the AMI field will print the value obtained from data blocks.

terraform plan

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the
following symbols:
  + create
Terraform will perform the following actions:
  # aws_instance.hello will be created
  + resource "aws_instance" "app_server" {
      + ami                                  = "ami-08d70e59c07c61a3a"
      ...
    }
Plan: 1 to add, 0 to change, 0 to destroy.
───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Note: You didn't use the -out option to save this plan, so Terraform can't guarantee to take exactly these actions if you
run "terraform apply" now.

Using data blocks will give us more flexibility in writing code.

The illustration is as follows:

07

of 07

Conclusion

So we know how to write Terraform configuration and run what commands so that Terraform can create resources on the infrastructure for us. And to better understand how Terraform builds resources, in the following lecture, we will talk about the life cycle of a resource in Terraform.

Tags: Terraform

Tutorial 02 | Terraform

01 of 07 Introduction

02 of 07 Create a Workspace and write a configuration

03 of 07 Initialize Workspace

04 of 07 Check the resource

05 of 07 Create resources

06 of 07 Data block

07 of 07 Conclusion

Tutorial 01 | Terraform

Tutorial 03 | Terraform

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