Creating VPC , Subnets , Routing table on AWS using Terraform

Terraform:

Terraform is an open-source infrastructure as a code software tool that provides a consistent CLI workflow to manage hundreds of cloud services. Terraform codifies cloud APIs into declarative configuration files.

Detailed Stepwise view of creating resources on AWS:

• Creating providers.tf file:

In this file, the cloud providers which we want to use are defined(in this case only AWS ) and the credentials are taken from profile created through AWS CLI.

provider "aws" {

  region  = var.aws_region #referenciing region from the var.tf file
  profile = "default"  #referencing profile configured voa AWS-CLI
}

• Creating a var.tf file:

In this step, I created a file called var.tf in which I stored all the values which a user can modify as per his/her need of launching the infrastructure. The reference of var.tf file is used to use variables defined in the file whenever required.

variable  "aws_region" {

    default = "ap-south-1"  #region where VPC wll eb launched
}


variable "vpc_cidr" {

    default = "10.0.0.0/16"  #CIDR declaration for VPC
}


variable "subnets_cidr" {

    type = list
    default = ["10.0.1.0/24" , "10.0.2.0/24"] #CIDR declaration for 2 subnets 
}


variable "availability_zones" {

    type = list
    default = ["ap-south-1a" , "ap-south-1b"]   #defining AZs for Subnets
 

}

• Creating a vpc.tf file :

In this file various resources are created like:

• VPC(a space on the cloud where user can provision resource):

#creating VPC
resource "aws_vpc" "vpc" {

    cidr_block = var.vpc_cidr


    tags = {

        Name = "my-vpc"
    }

}

• Subnets(a place inside VPC for a user to provision resources on the cloud):

resource "aws_subnet" "sbnt" {

    count  = length(var.subnets_cidr) #number of times the block will run is equal                                       to length of subnet's_cidr list
    vpc_id = aws_vpc.vpc.id

    /*when block runs for first time, first value form list subnet's_cidr will be                                  
     passed and when block runs for second time   
     second value form list subnet's_cidr will be passed*/
    
    cidr_block              = element(var.subnets_cidr , count.index) 
    availability_zone       = element(var.availability_zones , count.index)
    map_public_ip_on_launch = true


    tags = {

        Name = "My-Subnet-${count.index + 1}"
    }

}

• Internet Gateway(it serves two purposes: to provide a target in users VPC route tables for internet-routable traffic, and to perform network address translation (NAT) for instances that have been assigned public IPv4 addresses.):

#creating internet gateway for our subnets to be able to connect to internet
resource "aws_internet_gateway" "igw" {

    vpc_id = aws_vpc.vpc.id


    tags = {

        Name = "My-IGW"
    }

}

• Routing Table(it contains a set of rules, called routes, that are used to determine where network traffic from your subnet or gateway is directed):

#creating route table
resource "aws_route_table" "rt" {

    vpc_id = aws_vpc.vpc.id
    route {

        cidr_block = "0.0.0.0/0"
        gateway_id = aws_internet_gateway.igw.id
    }


    tags = {

        Name = "My-Public-Routing-Table"
    }

}

• Attaching Routing table to Subnets

#attaching route table to subnets created in order to provide access to internet.
resource "aws_route_table_association" "a" {

    count          = length(var.subnets_cidr)
    subnet_id      = element(aws_subnet.sbnt.*.id , count.index)
    route_table_id = aws_route_table.rt.id

}