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Resource and Data Blocks

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In this section, we will delve into two fundamental components of Terraform: Resource and Data Blocks. These blocks are essential for defining and managing infrastructure with Terraform.

What are Resource Blocks?

Resource blocks are the primary building blocks in Terraform. They define the infrastructure components that Terraform will manage. Each resource block specifies a type of resource and its configuration.

Key Concepts of Resource Blocks

  • Resource Type: The type of resource you want to create (e.g., aws_instance, azurerm_virtual_machine).
  • Resource Name: A unique name within the module to identify the resource.
  • Arguments: Configuration settings for the resource.

Example of a Resource Block

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"

  tags = {
    Name = "ExampleInstance"
  }
}

Explanation:

  • resource "aws_instance" "example": This line defines a resource of type aws_instance with the name example.
  • ami: The Amazon Machine Image (AMI) ID to use for the instance.
  • instance_type: The type of instance to create (e.g., t2.micro).
  • tags: A map of tags to assign to the instance.

What are Data Blocks?

Data blocks are used to fetch information from existing infrastructure. They do not create or modify resources but allow you to reference data from existing resources.

Key Concepts of Data Blocks

  • Data Source Type: The type of data source you want to query (e.g., aws_ami, azurerm_resource_group).
  • Data Source Name: A unique name within the module to identify the data source.
  • Arguments: Filters and settings to query the data source.

Example of a Data Block

data "aws_ami" "example" {
  most_recent = true

  filter {
    name   = "name"
    values = ["amzn2-ami-hvm-*-x86_64-gp2"]
  }

  owners = ["137112412989"]
}

Explanation:

  • data "aws_ami" "example": This line defines a data source of type aws_ami with the name example.
  • most_recent: A boolean indicating whether to fetch the most recent AMI.
  • filter: A block to specify filters for the AMI search.
    • name: The name of the filter.
    • values: The values to match for the filter.
  • owners: The AWS account ID of the AMI owner.

Practical Example: Using Resource and Data Blocks Together

Let's combine resource and data blocks in a practical example. We will fetch the latest Amazon Linux 2 AMI and use it to create an EC2 instance.

Example Code

provider "aws" {
  region = "us-west-2"
}

data "aws_ami" "latest_amazon_linux" {
  most_recent = true

  filter {
    name   = "name"
    values = ["amzn2-ami-hvm-*-x86_64-gp2"]
  }

  owners = ["137112412989"]
}

resource "aws_instance" "web_server" {
  ami           = data.aws_ami.latest_amazon_linux.id
  instance_type = "t2.micro"

  tags = {
    Name = "WebServer"
  }
}

Explanation:

  1. Provider Block: Specifies the AWS provider and region.
  2. Data Block: Fetches the most recent Amazon Linux 2 AMI.
  3. Resource Block: Creates an EC2 instance using the AMI ID fetched by the data block.

Exercises

Exercise 1: Create an S3 Bucket

Create an S3 bucket using a resource block.

resource "aws_s3_bucket" "example_bucket" {
  bucket = "my-example-bucket"
  acl    = "private"
}

Exercise 2: Fetch VPC Information

Fetch information about the default VPC using a data block.

data "aws_vpc" "default" {
  default = true
}

Exercise 3: Combine Resource and Data Blocks

Fetch the latest Ubuntu AMI and use it to create an EC2 instance.

provider "aws" {
  region = "us-west-2"
}

data "aws_ami" "latest_ubuntu" {
  most_recent = true

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"]
  }

  owners = ["099720109477"]
}

resource "aws_instance" "ubuntu_server" {
  ami           = data.aws_ami.latest_ubuntu.id
  instance_type = "t2.micro"

  tags = {
    Name = "UbuntuServer"
  }
}

Summary

In this section, we covered the basics of resource and data blocks in Terraform. Resource blocks are used to define and manage infrastructure components, while data blocks are used to fetch information from existing infrastructure. We also provided practical examples and exercises to reinforce the concepts. Understanding these blocks is crucial for effectively using Terraform to manage your infrastructure.

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