Assuming that you have already set up your environment, let’s get started with writing our first terraform code.

Create a main.tf file

In an empty folder, create a new file named main.tf. We will write all our code in this file for now. The name of the file actually does not matter but the extension does matter. Terraform actually reads all the files with .tf extension and treat them all the same. But for our readability, we create files with different name.
Content in main.tf

resource "aws_vpc" "tf_vpc" {
  cidr_block = "10.0.0.0/16"
}

First thing that you should notice is that the syntax does not resemble anything that already exists. Its a bit similar to JSON but if you look closely, it is not really. What this code essentially defines is, a resource of aws_vpc type with the name tf_vpc and the resource should have the property cidr_block = "10.0.0.0/16". Here the word ‘defines’ is really of prime significance. You see, terraform syntax is declarative. Which means you define a state what you want to have, and let terraform make sure that the state of your target is what you have defined. We are not asking it to create a VPC. We are merely defining it and letting terraform do its magic to create and manage it.
So we have declared a new VPC, but how do we ask terraform to read this file and perform the required action?

Executing terraform

To get started, let’s execute the code with two simple steps. We will learn the more sophisticated ways in the later stages of this guide.

Initialize with terraform init

Before we ask terraform to start executing the code, the terraform needs to download the stuff it needs to execute your code. Terraform only comes with a core component that reads the code user writes and passes it to something that can actually manage the users code. You can think of this as a plugin model where terraform is just managing lifecycle of the resources (in your code) which is deciding when to create, when to update and when to delete a resources, but how it will be created/updated/deleted is left to the plugin. This plugin in terraform language is called a provider. So in order to create resources on AWS, terraform needs to download the AWS provider. And how does it know what provider it should download? Well, it does not. You have tell it what provider your code needs. So we first need to update our main.tf file to add the provider.
Add content in main.tf:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0"
    }
  }
}

The code tells terraform that it needs a ‘hashicorp/aws’ provider with a version > 4.0, and it will be named as aws within this codebase. As you could imagine, our code can define multiple providers(within the same terraform block). Later on we will explore what could be the scenarios when we would need to do that.

Finally the content in main.tf should look like this:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0"
    }
  }
}
resource "aws_vpc" "tf_vpc" {
  cidr_block = "10.0.0.0/16"
}

Note: The position of the terraform block in the above code does not matter. In fact, it does not matter for any of the blocks you are going to create. Terraform just treats them as a set of blocks, and the sequence does not matter.

Within the folder where you created the main.tf file, run this following command

terraform init

With this command, terraform will look for any providers it needs to download. In our case, it will download the hashicorp/aws provider and make your system ready to execute your code. Yes, the resource creation does not take place with the init command. If you see a message that says Terraform has been successfully initialized!, you are good to go the next step. Now we will actually create the resource.

Create resource with terraform apply

The below command will instruct terraform to make sure the state that you have declared for your resources is actually present on AWS as well. In other words, go and create the resources in main.tf.

terraform apply

You should see a output with prompt at the end like:

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:

Take a moment and read what what the prompt says. It basically shows you the actions terraform is going to take. In terraform’s language, this called a plan. The green + signs represents things that are going to be created fresh. Later on we will encounter a few other sings and colors too. For now, go ahead and enter yes. If you see a message like this:

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

Congratulations, on creating your first resource using terraform.

Conclusion

We define terraform resources that we want to create in .tf along with the terraform providers that can manage those resources. Then we have initialize the terraform so that it download the providers mentioned. Finally we run the apply command to actually create the resource.

Updated: