Terraform

Terraform is a IAC tool, specifically used for provisioning. It is an open source tool developed by Hashicorp. It is allowing us to build image, manage and destroy infrastructure in few minutes. The biggest advantages of terraform is that it can support multiple platforms including private and public cloud providers such as Azure/AWZ/GCP/VMware/Physical machines.

Providers (AWS/Azure/GCP etc.,) helps terraform to manage the third party platforms through their APIs. Terraform uses HCL(Hashicorp Configuration Language) which is very simple language to define the infrastructure resources to be provisioned as a block of code. All infrastructure resources are defined in configuration files with tf extension. The source code can be maintained in source control system. So, it can be distributed to other teams as well.

NOTE: Remember, every objects that terraform manages known as resources. Terraform manages the object's entire life cycle starting from provisioning to destroying

Terraform has three phases

• Init
• Plan
• Apply

In init phase, terraform initiates the project and identify the providers. This provider will be used in the targeted environment.

In plan phase, terraform creates the plan to get the resources to target state.

In apply phase, terraform makes necessary changes to the plan to get the resources to desired state in the target environment.

Terraform maintains the record that state of the infrastructure. Based on this record, it can decide what action can be taken when updating the resources in particular platform such as AWS and Azure.

It is Terraform's responsibility to maintain the defined state for all the resources in the code at all time.

Terraform can read the attribute of the existing resources by configuring datasource. This can be used to configure other datasource within Terraform. It can also import other resources outside of Terraform and manages them.

HashiCorp Configuration Language (HCL)

HCL consists of blocks and arguments.

<BLOCK> {
    <ARGUMENTS>
}

Arguments will be in key value format and represents configuration data.

<BLOCK> {
    <KEY1>=<VALUE1>
    <KEY2>=<VALUE2>
}

Block contains the information of infrastructure platform and set of resources to be created within the platform.

Block contains resource name and resource type.

Example

Let us see an example to create a file in local laptop/desktop using terraform.

resource "local_file" "names" {
    filename = "/Users/satheeshpandian.j/Documents/Sats/Learning/Terraform/names.txt
    content = "Satheesh \nPandian \nJeganathan"
}

Explanation

resource "local_file" "names" => Block

Below is the argument filename = "/Users/satheeshpandian.j/Documents/Sats/Learning/Terraform/names.txt" content = "Satheesh \nPandian \nJeganathan"

Type of the block is resource which is identified by keyword resource in the beginning of the block.

local_file => local is provider + file is type of resource

local_file => Resource type we want to create. This is fixed value and will be changed based on the provider.

names => Resource name. It can be anything.

As it is file type of resource and needs to be a local type provider, filename is the mandatory argument. Refer this link

Now, we need to run the file (local-file-creation.tf) we created. To do so, we need to initialize the project using terraform init command

Next, we need to ensure if whatever resource needs to be created, will it be there. To check this, you need to run terraform plan command

If you observe the above output, you can see the filename, along with content (NOT VISIBLE as it is not yet applied), file permission etc. Terraform will create additional attributes as an arguments alone with user provided attributes.

Now, let us update the resource we created (local file).

resource "local_file" "names" {
    filename = "/Users/satheeshpandian.j/Documents/Sats/Learning/Terraform/names.txt"
    content = "I am Satheesh and this is terrform update example"
}

Now, let us destroy the resource we created (local file).

To hide the file content during terraform plan / terraform apply, use the below code

resource "local_sensitive_file" "games" {
    filename = "/Users/satheeshpandian.j/Documents/Sats/Learning/Terraform/names.txt"
    content = "I am Satheesh and this is terraform update example"
}

For AWS Provider

resource "aws_instance" "app_server" {
  ami           = "ami-830c94e3"
  instance_type = "t2.micro"

  tags = {
    Name = "ExampleAppServerInstance"
  }
}

Provider	Link
AWS	https://registry.terraform.io/providers/hashicorp/aws/latest
Azure	https://registry.terraform.io/providers/hashicorp/azurerm/latest
Google	https://registry.terraform.io/providers/hashicorp/google/latest