Terraform is an IAAC tool used to automate programmatic infrastructure provisioning. Here in this guide, I will first discuss what is AWS VPC. Then I will discuss terraform. After this, I will walk you through the different steps to write a code using Terraform to create a custom AWS VPC using subnet, internet gateway, and routing tables.

What is AWS VPC?

AWS VPC is a service that helps users create a virtual network on the AWS cloud platform. In the VPC, users can create their own public or private subnets, routing tables, internet gateways, and NAT gateways. Users can create a security group associated with a VPC for better security, here users define inbound and outbound rules. NACLs are used at the subnet level to allow or deny particular IPs when trying to access the subnet. AWS VPC gives users complete control over the virtual network on the AWS cloud platform. Overall we can say that this level of control enables users to create a custom virtual network to build a secure and scalable architecture for applications.

What is Terraform?

Terraform is an Infrastructure as Code(IAAC) tool that is used to define and provision infrastructure using a declarative configurational language called HashiCorp Configuration language(HCL). It has a simple syntax that helps to provision infrastructure in multiple cloud platforms. Using terraform increases the speed and reliability. It helps organizations to automate programmatically their infrastructure provisioning. Terraform’s version control feature enables teams in an organization to manage infrastructure configurations as code, facilitating collaboration and also ensuring the tracing of changes over time. Its simplicity, cross-platform compatibility, and automation capabilities make it an essential tool for an organization to maintain control, reliability, and scalability.

How To Create AWS VPC Using Terraform?: A Step-By-Step Guide

The following are the steps that guides you on how to create AWS VPC using Terraform:

Step 1: First mention the provider and region in which you want to create VPC.

provider.tf

provider "aws" {
    region = "us-east-1"
}

Step 2 : Create a VPC . Here mention the CIDR block and give a name to the VPC .

create_vpc.tf

resource "aws_vpc" "main" {
  cidr_block       = "10.0.0.0/16"
  instance_tenancy = "default"

  tags = {
    Name = "vpc"
  }
}

Step 3 : Then create a subnet inside the VPC with the following subnet.tf file:

resource "aws_subnet" "main" {
  vpc_id     = aws_vpc.main.id
  cidr_block = "10.0.1.0/24"
  map_public_ip_on_launch=true
  tags = {
    Name = "Public-Subnet"
  }
}

Step 4 : But the subnet is isolated now . If you create an EC2 instance inside this subnet then you can not connect the EC2 instance as it is present in an isolated environment . So you need an internet gateway .

internet_gateway.tf

resource "aws_internet_gateway" "igw" {
  vpc_id = aws_vpc.main.id

  tags = {
    Name = "IGW"
  }
}

Step 5 : Create a route table and associate the route table with subnet . Here in the route all the traffic is passed through internet gateway .

route_table.tf

resource "aws_route_table" "rt" {
  vpc_id = aws_vpc.main.id

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

  tags = {
    Name = "route_table"
  }
}

route_subnet_association.tf

resource "aws_route_table_association" "a" {
  subnet_id      = aws_subnet.main.id
  route_table_id = aws_route_table.rt.id
}

Step 6 : After this execute all these terraform files using the below commands one by one .

terraform init
terraform plan
terraform apply

Step 7: Check on your AWS console whether the VPC is created or not

• Now if you want to delete all the resources created through terraform , then write this command .

terraform destroy

Best Practices of using Terraform for AWS VPC

The following are the best practices of using Terraform:

• Modularize Your Code: It helps in breaking your Terraform configuration into reusable modules for improving readability, manageability, and reusability of your infrastructure code.
• Use Version Control: To keep your Terraform code in a version control system like Git for tracking changes and collaborations with others, and rollback if necessary.
• State Management: It helps in using the remote state backends, such as S3 with DynamoDB for state locking, to manage and secure your Terraform state files effectively.
• Environment Segregation: It helps in creating a separate workspaces or use different state files for different environments (development, staging, production) to avoid conflicts and manage infrastructure lifecycle better.

Trouble shooting issues of Terraform

The following are the trouble shooting issues of Terraform:

• Syntax Errors: On using terraform fmt and terraform validate we can check for the syntax errors and ensure your configuration is well-formed before applying changes.
• Resource Conflicts: By Identifying and resolving the resource conflicts by carefully managing resource naming and using the terraform plan command we can review the changes before applying them.
• State File Issues: For fixing the state file corruption or inconsistencies can be done by using terraform state commands to inspect, modify, or repair the state file as needed.
• Dependency Management: On handling the dependencies correctly by using Terraform’s built-in mechanisms like depends_on to explicitly define resource dependencies and ensure proper resource creation order.

Conclusion

Here first we learned basics about AWS VPC and terraform . Then followed the steps to create an AWS VPC . Here inside the VPC we have created a public subnet , an internet gateway which helps the traffic to go in and out of the subnet and finally created a route table and associated with the subnet.

AWS VPC Using Terraform – FAQs

What is a subnet in VPC ?

When you are creating a VPC you provide a CIDR block (a range of IP address) . Like that , in subnet we provide a segment of IP addresses which helps the VPC to organize and manage its IP addresses .

What are NAT gateways used for ?

NAT gateways are used to give internet connectivity to the resources which are created using private subnet .

How public subnet is different from private subnet ?

Public subnet access internet(in and out) by using Internet gateway . But private subnets does not not use internet gateway to access internet , rather here NAT gateways are used for outbound internet access . We can not connect private subnet from outside .

How to ensure that EC2 instance inside the VPC gets internet connectivity ?

To ensure EC2 instance gets internet connectivity , you should place the instance in a public subnet that has a route to internet gateway in its route table.

What is the use of route table in VPC ?

Route table contains a set of routes which is used to determine where network traffic should be directed in the VPC .