Note_Tech

All technological notes.

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Terraform - IaC

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• Terraform - IaC
  • IaC
  • Terraform
    • Terraform provider versioning
  • Provisioner

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IaC

• Infrastructure As Code (IaC)

  • instead of using UI, use code to manage infrastractures.

• Benefits

  • support code reusability
  • code can be instegrated with git/VCS to control version
  • enable code review
  • enable audit log

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Terraform

• Language
  • HCL (Hashicorp Configuration Language)

• Resole dependency

  • tf reads all .tf files and create a resource graph to determine the sequence of managing resources.

• tf workflow:

  • define resource with .tf
  • terraform plan to preview what will be applied
  • terraform apply to implement resource management.
    • only the updated resources need to be changed

• Terraform core contains

  • the language interpreter
  • CLI
  • how to interact with providers, not cloud provider API.

• Terraform registry

  • a platform to found different provders that support terraform.
  • https://registry.terraform.io/

• Terraform providers

  • contains the code to interact with API of cloud provider.
  • shipped separately whith their own version numbering
    • must be installed separately using terraform init
    • By default, tf download the latest available version of provider.
    • Good practices:
      • specify the provider with version in the terraform {} block.

# AWS provider
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 6.0"
    }
  }
}

# custom provider
terraform {
    required_providers{
        mycloud = {
            version = ">= 1.0.0"
            source = "mycorp/mycloud"   # tf cloud's private registry
        }
    }

    required_version = ">= 0.14"
}

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• Provider Configuration

provider "aws" {
    region = "us-east-1"
}

• Using alias meta-argument with multiple providers

provider "aws" {
    region = "us-east-1"
}

provider "aws" {
    alias = "eu"        # using alias
    region = "eu-west-1"
}

resource "aws_instance" "myinstance"{
    provider = aws.eu
}

module "mymodule" {
    source = "./mymodule"
    providers = {
        aws = aws.eu
    }
}

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Terraform provider versioning

• Terraform provider versioning follows semantic versioning:
  • MAJOR.MINOR.PATCH
    • MAJOR: new breaking changes
    • MINOR: new features
    • PATCH: bug fixes only

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Provisioner

• Provisioner

  • enable actions that cannot be directly expressed through resource configurations.
  • separate flows that cannot be fully controlled by terraform.
  • add a considerate amount of complexity and uncertainty
    • if something are misconfigured, it might lead time out, making a tf workflow fail.
  • requires more coordination
    • ie, a script for apt update requires:
      • sg
      • internet access
      • VPN, if internet is not available

• Types of provisioner

  • Local-provisioner
    • execute scripts/commands locally.
  • Remote-provisioner
    • execute scripts/commands remotely, like on a VM.
  • Packer
    • used to build and launch AMI.
  • Cloud init
    • using user_data and AWS API to pass a script required only at creation.

• !ONLY USE Provisioner AS LAST RESORT.