It's the moment of truth! In this chapter, you will build your first real infrastructure with Terraform, putting together everything you've learned: the AWS services from Part II and the Terraform language from Part III. We start with the foundation of any architecture: a VPC with subnets. Remember the concepts from Chapter 6, which you will now write in code.

Throughout the chapter, we will set up a simple but complete architecture:

In this subchapter, we create the VPC, a subnet, and basic internet connectivity. In the following ones, we will add the server, the firewall, the IP, and the outputs.

Every project starts by configuring the AWS provider (remember subchapter 11.1). We create a file, for example main.tf:

The VPC is our private network (remember subchapter 6.1). With a range of 10.0.0.0/16:

• cidr_block defines the address range (subchapter 6.1).
• The enable_dns_* options allow resources to have DNS names (useful for the server to have a name).
• tags gives a human-readable name to the resource (it's highly recommended to tag everything).

Inside the VPC, we create a subnet (subchapter 6.2). We place it in a specific availability zone:

Notice vpc_id = aws_vpc.principal.id: it's a reference (subchapter 10.3). We tell the subnet "you belong to the VPC I created before." This creates the dependency: Terraform knows it must create the VPC first.

map_public_ip_on_launch = true makes resources in this subnet automatically receive a public IP, part of what makes it "public."

For the subnet to be truly public, it needs a gateway to the internet (subchapter 6.3):

This creates the Internet Gateway and connects it to our VPC.

The Internet Gateway alone is not enough: you have to tell the subnet to use that gateway to access the internet. This is done with a route table (subchapter 6.4):

This is exactly what we saw in subchapter 6.4: the route 0.0.0.0/0 → Internet Gateway is what makes the subnet public. The route_table_association connects the table to our subnet.

With these five steps, you have a functional network:

If you now run terraform init and terraform plan (subchapter 11.4), you would see something like:

And with terraform apply (typing yes), Terraform would create the entire network in the correct order automatically, thanks to the references between resources.

The power of this: you just defined a complete network in a few lines of text. You can reuse, version in Git, and recreate this same configuration as many times as you want (remember the problems of manual provisioning from Chapter 9). And if you delete it with destroy, it disappears cleanly.

• Every architecture starts with the network: VPC + subnets + connectivity.
• The steps: configure the provider, create the VPC, the subnet, the Internet Gateway, the Route Table, and its association.
• References (aws_vpc.principal.id) connect resources and create dependencies, so Terraform creates them in the correct order.
• The route 0.0.0.0/0 to the Internet Gateway is what makes the subnet public (just as we saw in Chapter 6, now in code).
• Tag (tags) all your resources with readable names: it's a good practice.

In the next subchapter, we will put an EC2 server inside this public subnet.