Hello. In this tutorial, we will understand Terraform locals.
1. Introduction
Terraform is a tool for building, changing, and versioning the infrastructure safely and efficiently. It is used to manage the infrastructure of the popular cloud service providers and custom in-house solutions. It helps manage both low-level (Compute, Storage, Networking, etc.) and high-level components (such as SaaS, DNS, etc.) Terraform deployment automation is divided into different sections i.e. –
- IaaC – IaaC is popularly known as the Infrastructure as a Code wherein the infrastructure is described using a high-level configuration syntax. This allows a blueprint of the infrastructure which can be deployed, versioned, and shared for re-use
- Execution Plans – Terraform has a planning step where it generates an execution plan. The execution plan tells the administrator what Terraform will do once applied and helps to avoid any surprises when it creates the infrastructure
- Resource Graph – Terraform builds a graph of all the resources and parallelizes the creation and modification of non-dependent resources. This offers insights into learning the dependencies in their infrastructure
- Change Automation – Terraform allows to apply of complex changesets to the infrastructure with minimal human intervention
1.1 Configuration language
Terraform has its configuration language designed to meet the infrastructure automation requirements. The main purpose of this language is to declare resources and a group of resources (gathered into a module) represents a larger unit of configuration. Language syntax consists of a few elements i.e. – Blocks, Arguments, and Expressions.
- Blocks – Containers for other contents and represents the object configuration
- Arguments – Assign a value to the name and appear within the blocks
- Expressions – Represents a single value, referenced value, or combination of other values
1.2 Steps
To create the infrastructure via the Terraform scripts following commands need to be executed.
terraform init– Initializing the new or existing terraform configurationterraform plan– Generate the execution plan from the resources specified in the fileterraform apply– Create the infrastructure from the resources specified in the fileterraform destroy– Destroy the created infrastructure
1.3 Terraform locals
The locals in Terraform assign a name to an expression that can be used multiple times within a module. The values are defined in the locals blocks as shown in below syntax –
locals {
some_key = "some_value"
}
2. Practice
Let us dive into some practice stuff from here. You’re free to choose the IDE of your choice. I am using Visual Studio Code as my preferred IDE for the development with the HashiCorp Terraform extension installed. The extension offers syntax highlighting and other editing features for Terraform files using the Terraform language server.
2.1 Pre-requisite
To proceed we will be needing an AWS CLI user having the right set of permissions required for creating the infrastructure. I am using an existing user and attached the EC2 full access policy attached to this user so that the IAM user can successfully create the required infrastructure. The access and secret key generated for the user will be used in the project’s root variables.tf file.
2.2 Creating an EC2 instance and using the locals
2.2.1 Variable file
The file contains the declarations required to create the EC2 instance such as amazon machine image id, instance type, zone id, etc, and AWS login details for the provider block. Add the below code to the file.
variables.tf
# ec2 variables
variable "ami_id" {
default = "free_tier_ami_id" # remember to check for free-tier ami id before runnning the script to avoid unwanted money
}
variable "instance_type" {
default = "t2.micro" # creating instance under free tier
}
variable "zone_id" {
default = "ap-south-1a"
}
variable "key_pair" {
default = "ec2_keypair_filename"
}
variable "subnet_id" {
default = "subnet_id"
}
variable "vpcid" {
default = "vpc_id"
}
variable "instance_count" {
default = 1
}
# volume variables
variable "ebs_volume_name" {
default = "/dev/xvda"
}
variable "ebs_volume_size" {
default = 8 # free tier configuration
}
variable "ebs_volume_type" {
default = "gp2"
}
# iam variables
variable "cli_usr" {
default = "your_aws_cli_usr_access_key"
}
variable "cli_usr_key" {
default = "your_aws_cli_usr_secret_key"
}
# aws region
variable "region" {
default = "ap-south-1"
}
2.2.2 Implementation file
Add the following code to the main file responsible to set up the implementation. The file will refer to the local environment variables while setting tags for the resource and specifying the CIDR blocks for the security group,
main.tf
provider "aws" {
region = var.region
access_key = var.cli_usr
secret_key = var.cli_usr_key
}
# creating local variables
locals {
environment = "development"
cidr_block = "0.0.0.0/0"
}
# security group resource
resource "aws_security_group" "ec2-sg" {
vpc_id = var.vpcid
ingress = [
{
description = "ssh"
from_port = 22
to_port = 22
protocol = "tcp"
cidr_blocks = ["${local.cidr_block}"]
ipv6_cidr_blocks = null
prefix_list_ids = null
security_groups = null
self = null
}
]
egress = [
{
description = "all-open"
from_port = 0
to_port = 0
protocol = "-1"
cidr_blocks = ["${local.cidr_block}"]
ipv6_cidr_blocks = null
prefix_list_ids = null
security_groups = null
self = null
}
]
tags = {
"label" = "${local.environment}"
}
}
# ec2 resource
resource "aws_instance" "ec2_example" {
ami = var.ami_id
availability_zone = var.zone_id
instance_type = var.instance_type
key_name = var.key_pair
count = var.instance_count
security_groups = ["${aws_security_group.ec2-sg.id}"]
subnet_id = var.subnet_id
ebs_block_device {
device_name = var.ebs_volume_name
volume_size = var.ebs_volume_size
volume_type = var.ebs_volume_type
delete_on_termination = true
}
tags = {
"label" = "${local.environment}"
}
}
3. Code Run
Navigate to the project directory containing the above scripts and open the terminal. Execute the below commands in the respective order within the directory.
Commands
-- step1: initializing the new or existing terraform configuration -- terraform init -- step2: generating the execution plan -- terraform plan -- step3: building the infrastructure -- -- auto-approve flag skips interactive approval of the plan before applying terraform apply --auto-approve -- step4: destroying the infrastructure -- -- auto-approve flag skips interactive approval of the plan before applying terraform destroy --auto-approve
4. Demo
Once the terraform script is successfully executed head over the AWS console to confirm that the EC2 instance is successfully created on the EC2 dashboard.
That is all for this tutorial and I hope the article served you with whatever you were looking for. Happy Learning and do not forget to share!
5. Summary
In this tutorial, we learned an introduction to Terraform, Locals, and EC2 instances created in the AWS portal. You can download the source code from the Downloads section.
6. Download the Project
This was a tutorial on learning and implementing Terraform locals.
You can download the full source code of this example here: How to use Terraform locals
