Terraform Data Sources

Data Sources

Data resources in Terraform allow you to fetch information or query existing resources outside of the configuration
Data resources do not create or manage infrastructure. They provide a way to reference external data
Immutable Data: Data resources provide a way to interact with external data, but they don't modify that data. They are read-only.
Data Blocks: The structure of a data block is similar to a resource block, but with the data keyword.
Dynamic Values: You can use dynamic values from data resources in various places within your Terraform configuration.

Syntax:

data "type" "name" {
    argument1 = "value1"
    argument2 = "value2"
    ......... = "......"

    filter {
    name = "<name>"
    values = "<value>"
    }

    filter {
    name = "<name>"
    values = "<value>"
    }
}

Example:

00_provider.tf

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

provider "aws" {
  region = var.aws_region

  default_tags {
    tags = {
      Terraform = "yes"
      Owner     = var.owner
    }
  }
}

01_ec2.tf

resource "aws_instance" "myec2" {
  ami = data.aws_ami.amzn_linux_2023_latest.id # fetching Latest Amazon Linux AMI id from data sources
  instance_type = var.ec2_instance_type

  tags = {
    Name = "Linux2023"
  }
}

02_variables.tf

variable "aws_region" {
  description = "AWS Region In Which Resources will be Created"
  type        = string
  default     = "us-east-1"
}

variable "owner" {
  description = "Name of the Engineer who is creating Resources"
  type        = string
  default     = "Venkatesh"
}

# AMI section we are going to use data resources to fetch latest Amazon Linux AMI
/*variable "ec2_ami" {
  description = "AWS EC2 AMI Amazon Linux 2023"
  type        = string
  default     = "ami-0df435f331839b2d6" # Amazon Linux 2023
}*/

variable "ec2_instance_type" {
  description = "EC2 Instance Type"
  type        = string
  default     = "t2.micro"
}

03_data.tf

data "aws_ami" "amzn_linux_2023_latest" {
    most_recent = true
    owners = [ "amazon" ]

    filter {
      name = "name"
      values = [ "al2023-ami-2023*" ]
    }

    filter {
      name = "architecture"
      values = [ "x86_64" ]
    }

    filter {
      name = "root-device-type"
      values = [ "ebs" ]
    }

    filter {
      name = "virtualization-type"
      values = [ "hvm" ]
    }
}

In the above example, We are trying to fetch Latest AWS EC2 Amazon Linux 2023 AMI (located in us-east-1) based on following filters

1. most_recent = true, to fetch latest AMI
2. name = al2023-ami-2023* to fetch AMI name starting with al2023-ami-2023
3. architecture = x86_64 to fetch AMI of type x86_64
4. root-device-type = ebs to fetch AMI of root device type ebs 5. virtualization-type = hvm to fetch AMI of virtualization type hvm
Filtering with similar pattern on AWS Console you should see,
- AWS launch Console:
- AWS Public AMI Console (EC2 Page ==> AMI):
For additional filter type, Please ref to AWS AWS CLI describe-images
Lets Execute Terraform commands to understand data source behavior
1. terraform init : Initialize terraform
2. terraform validate : Validate terraform code
3. terraform fmt : format terraform code
4. terraform plan : Review the terraform plan
5. terraform apply : Create Resources by terraform
  - Example of terraform plan or terraform apply
  - Plan output shows the Latest AWS EC2 Amazon Linux 2023 AM

terraform apply

  $ terraform apply
  data.aws_ami.amzn_linux_2023_latest: Reading...
  data.aws_ami.amzn_linux_2023_latest: Read complete after 1s [id=ami-0a3c3a20c09d6f377]

  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.myec2 will be created
  + resource "aws_instance" "myec2" {
      + ami                                  = "ami-0a3c3a20c09d6f377"
      + arn                                  = (known after apply)
      + associate_public_ip_address          = (known after apply)
      + availability_zone                    = (known after apply)
      + cpu_core_count                       = (known after apply)
      + cpu_threads_per_core                 = (known after apply)
      + disable_api_stop                     = (known after apply)
      + disable_api_termination              = (known after apply)
      + ebs_optimized                        = (known after apply)
      + get_password_data                    = false
      + host_id                              = (known after apply)
      + host_resource_group_arn              = (known after apply)
      + iam_instance_profile                 = (known after apply)
      + id                                   = (known after apply)
      + instance_initiated_shutdown_behavior = (known after apply)
      + instance_lifecycle                   = (known after apply)
      + instance_state                       = (known after apply)
      + instance_type                        = "t2.micro"
      + ipv6_address_count                   = (known after apply)
      + ipv6_addresses                       = (known after apply)
      + key_name                             = (known after apply)
      + monitoring                           = (known after apply)
      + outpost_arn                          = (known after apply)
      + password_data                        = (known after apply)
      + placement_group                      = (known after apply)
      + placement_partition_number           = (known after apply)
      + primary_network_interface_id         = (known after apply)
      + private_dns                          = (known after apply)
      + private_ip                           = (known after apply)
      + public_dns                           = (known after apply)
      + public_ip                            = (known after apply)
      + secondary_private_ips                = (known after apply)
      + security_groups                      = (known after apply)
      + source_dest_check                    = true
      + spot_instance_request_id             = (known after apply)
      + subnet_id                            = (known after apply)
      + tags                                 = {
          + "Name" = "Linux2023"
          }
      + tags_all                             = {
          + "Name"      = "Linux2023"
          + "Owner"     = "Venkatesh"
          + "Terraform" = "yes"
          }
      + tenancy                              = (known after apply)
      + user_data                            = (known after apply)
      + user_data_base64                     = (known after apply)
      + user_data_replace_on_change          = false
      + vpc_security_group_ids               = (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: yes

  aws_instance.myec2: Creating...
  aws_instance.myec2: Still creating... [10s elapsed]
  aws_instance.myec2: Still creating... [20s elapsed]
  aws_instance.myec2: Creation complete after 25s [id=i-0acb2a1d622c55a02]

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

  Venkatesh@LenovoPC MINGW64 /d/StudyRelated/terraform-beginners-guide/11-Terraform-Data-Sources (main)