Terraform Basic Blocks

Fundamental block

• Terraform Block
  - For setting up terraform and download it’s related versions.
  - For configuring some behaviours.
  - It contains information about:- Terraform version, Provider requirement and Terraform state Figure 1.

Figure 1

• Provider Block
  - For Interacting with API’S.
  - Terraform Rely on provider to interact with remote systems.
  - Declare providers in required_providers to install and use them
  - Belong to Root module.
  - We can also change settings of required providers like Figure 2.

Figure 2

• Resource Block
  - Each Resource block define one or more Infrastructure Objects Figure 3.
  - Resource syntax.
  - Resource behaviours.
  - Provisioners:- We can configure Resource post-creation actions

Figure 3

Terraform Block / Setting Block / Configuration Block

• Only constant values can be used.
• Can not use any variables and inbuilt functions of terraform.
• We are going to provide the required provider inside the Terraform Block.
• For example
• Required_version { } is the CLI lock so there is no version mismatch.
• Required_providers { } on terraform init download the all the required things.
• Backend { } for storing the state of configuration to store state information we add backend

Understanding terraform required_version

• ~> This will allows the rightmost digit to increment for example 2.0.7 and it can also be 2.0.9, 2.0.10.
• = This is for the exact equal mostly in the production environment.

Understanding required_providers

• This is where we give information about providers which is needed to install to interact with the API’s

Important note about required_version

• “~> 1.12” It will change the right most value and it will change to “1.13” and then it can break. So it’s good to use “~> 1.12.1” so it will stay on the major release

Terraform Providers

• When we do terraform init it contact terraform registry and it will download Terraform AWS Providers
• Terraform AWS provider → terraform apply → AWS API and then it will create AWS resources
• Providers and separate version and release cycle
• 3 things that we need about Terraform Providers
• Provider Requirements
  - This is in the Terraform Block
  - Example aws = { source = “”, version =“”}
• Provider configuration
  - This is in the Provider Block
  - To configure the providers
  - Example Provider “aws” { profile =“default”, region=“us-east-1”}
• Dependency lock files
  - file name .terraform.loc.hcl and it’s there is root folder
  - Version related information is locked here
• Required Providers
  - For example aws = { source = “”, version =“”}
  - This aws should be module specific and be unique per module
  - Can choose name instead of aws likemyaws, aws1, aws2
  - But preferred way of choosing local name is to use preferred local name of that provider
  - Source is the primary location from where we can download.
• Terraform Providers Registry
  - Location is registry.terraform.io
  - Can get module and providers
• Providers Type
  - Have Official Badge:- Maintained by HashiCorp
  - Verified Badge:- made by 3rd party developer
  - Community:- Made by individual maintainers
  - Archived:- Older versions

Understanding the Providers Block

• In AWS configure for authentication on AWS we do have default profile so in provider block we add profile = “default”
• It will take credential from AWS Configure settings

Multiple providers configurations #important

• Multiple configurations for same provider and which one to choose per resource or per module basis.
• To support multiple regions.
• For example
  - Provider “aws” {region = “eu-central-1”, alias = “eu-central-1”}
  - Resource “aws_vpc” “vpc-eu-central-1” { provider = aws.eu-central-1 }

Dependency lock file

• When we do terraform init the .terraform.lock.hcl got created. It contains the version constraints and record files .terraform folder contain the provider information.
• Where we do terraform apply the terraform.tfstate get created. It is terraform configuration local database. What you create in the cloud it’s equivalent reference will be created locally.
• Dependency lock file (.terraform.lock.hcl):- After selecting a specific version of each dependency using version constraints Terraform remembers the decision it made in dependency lock file so that it can make the same decision in the future.
• Lock file track only provider dependency. For module it continue to use exact version constraint to ensure that terraform will always select the same module version.
• Checksum verification:- Terraform matches that each package it install matches at least one of the checksums it previously recorded in the lock file.
• Terraform configuration
• Provider version
• Module version
• Importance of dependency lock file
• For example AWS >= 2.0 if lock file then it will add the latest version and if there is lock file then the version could be (2.50.0) to maintain the consistency

Upgrade Terraform Provider Version

• command:- terraform init -upgrade it will upgrade the terraform provider