Scenario: Create an Ec2 machine in AWS with existing security group and ensure you have tags

• To create this we will be using Local Values and Datasources
• Local Values help in creating the expression once and reuse it multiple times
• DataSource help in fetching the values from provider. For finding datasources google with expression terraform datasource <provider> <resource> eg terraform datasource aws securitygroup
• The terraform script

provider "aws" {
    
}

## Create variable value for reuse with in template
locals {
  common_tags   = {
      Name      = "learning"
      Owner     = "DevOps"
  }
}


data "aws_security_group" "mysecuritygroup" {
    name    = "Openall"
}


resource "aws_instance" "firstec2" {
    ami                             = "ami-003634241a8fcdec0"
    instance_type                   = "t2.micro"
    key_name                        = "terraform"
    vpc_security_group_ids          = [ data.aws_security_group.mysecuritygroup.id ]
    associate_public_ip_address     = true
    tags                            = local.common_tags

}

Scenario: Create a VPC with variable number of subnets

• Look into Terraform functions [from here]
• We have a terraform template which looks like this

variable "vpccidr" {
  description   = "cidr of the vpc"
  default       = "192.168.0.0/16"
}

variable "subnetcidrs" {
  description   = "subnet cidrs"
  type          = list(string) 
  default       = ["192.168.0.0/24", "192.168.1.0/24", "192.168.2.0/24"]
}

variable "nameofvpc" {
  description = "name for vpc"
  default = "myvpc"
}

provider "aws" {
    
}

resource "aws_vpc" "created" {
    cidr_block  = var.vpccidr
    tags        = {
        Name    = var.nameofvpc
    }
}

resource "aws_subnet" "subnets" {
    count       = length(var.subnetcidrs)
    vpc_id      = aws_vpc.created.id
    cidr_block  = var.subnetcidrs[count.index]
  
}

output "vpcid" {
  value = aws_vpc.created.id
}

Scenario: Rather than copying the above terraform script again try to reuse the tempalte to create an ec2 instance inside your vpc

• How to make template reusable?
• Answer is Terraform modules and we will be using modules and registry