Terraform

What is Terraform

Terraform is a Infrastructure as a Code solution that allows provisioning of resources within the cloud. It can be AWS, Google, Azure and any other ones.

Benefits of Terraform

• It is a great tool for versioning, deploying and changing the infrastructure of your cloud safely and efficiently
• It is compatible with many cloud providers and services
• It allows you to reuse templates

Terraform Architecture

Terraform has “Terraform Core” which takes the configuration files, terraform state and it figures out how to apply changes and ensure it matches what we want to do. To achieve that, it uses Terraform Providers.

Terraform also uses Terraform State Files which have information about the current state of your resources. Terraform also has a concept of Local Backend and Remote Backend which essentially mean that state is either stored locally or remotely.
Example of Terraform File

How to use Terraform CLI

terraform init - Initialises terraform and creates a terraform state file within it
terraform plan - Shows me what will change or what will be created
terrafirn deploy - it will deploy and apply all changes/create resources
terraform destroy - It destroys all resources

What happens when you run init

On init, Terraform downloads the provider that is defined from Terraform registry and puts it in providers directory. It also creates a lock file that contains all information about dependencies and providers.

What happens when you run plan

it compares the state with what you currently have in your terraform files

What happens when you run apply

It shows you what plan would show you, asks you whether you want to apply changes and then it does this

What happens when you run destroy

on destroy, terraform destroys all resources.

IAM Roles

• RDSFullAccess to provision DB

• EC2 FullAccess to provision EC2 instance

• IAMFullAccess to be able to provision some policies

• AmazonS3FullACcess to have acess to S3

• AmazonDynamodbfullaccess to create dynamodb tables

• AmazonRoute53fullaccess to have access to Route53 (DNS)

Difference between variable.tf and *.tfvars

variable.tf is where all vars are declared and it may or may not have default value. *tfvars is where variables have a value assigned

data

data allows me to reference existing resources in AWS

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

Variables

in Terraform, there are 2 types of variables:

Input Variables

Input Variables that can be called with var.<name>

   variable "aws_profile" {  
	   description = "aws profile"  
	   type = string  
	   default = "my_profile"  
   }  

Those you will be able to specify when you run terraform apply

Setting Input Variables

There’s a specific order in which you can specify input variables

1. Manual entry during plan/apply
2. Default value in declaration block
3. TF_VAR_{name} env var
4. terraform.tfvars file
5. *.auto.tfvars file
6. Command line -var or -var-file (-var should probably be stored in github secrets or AWS equivalent of that)

Types

Primivite

• string
• number
• bool

Complex

• list(type)
• set(type)
• map(type)
• object({attrName = type})
• tuple([type])

Sensitive Variables

Sensitive data such as passwords to a DB should not be stored as a hardcoded value but should be passed in runtime by using some kind of secrets manager. Also, to make sure that those won’t be outputted in a terminal, when defining the variable, you have to specify sensitive = true

variable db_pass {  
	type = string  
	sensitive = true  
}  

Local Variables

Those are scoped within a function and they should be used when you have to repeat yourself multiple times within that function

locals {  
	service_name = "My Service"  
	owner = "DevOps Dir"  
}  

Output Variables

These are used to give an output of what has been created. It can be an instance of an IP when instantiating EC2 etc.

output "instance_up_addr" {  
	value = aws_instance.instance.public.ip  
}  

Project Organisation and Modules

Module

Module is a “container” for multiple resources. It can consist of a few .tf files. It is a way to package and reuse configs with Terraform.

Types of Modules

How to create a good module

• Raises the abstraction level from the base resource types

• Groups resources in a logical fasion

• Exposes input vars to allow necessary customisation and composition

• Add useful defaults

• Return outputs to make further integrations possible

Deployment to multiple environments

There are always situations where you need to deploy an app to multiple environments (prod, dev, staging etc.). For that reason you can use two approaches

Workspaces

Workspaces are named sections within a single backend

File Structure

Directory layout with a use of modules

Guides

How to create Remote Backend with S3 and DynamoDB with Terraform
How to conditionally create a resource with Terraform