docs: add Terraform certification notes and tasks

terraform/task-35.md

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+# Assignment
+
+The Nautilus DevOps team is automating VPC creation using Terraform to manage networking efficiently. As part of this task, they need to create a VPC with specific requirements.
+
+For this task, create an AWS VPC using Terraform with the following requirements:
+
+The VPC name datacenter-vpc should be stored in a variable named KKE_vpc.
+
+The VPC should have a CIDR block of 10.0.0.0/16.
+
+Note:
+
+The configuration values should be stored in a variables.tf file.
+
+The Terraform script should be structured with a main.tf file referencing variables.tf.
+
+The Terraform working directory is /home/bob/terraform.
+
+Right-click under the EXPLORER section in VS Code and select Open in Integrated Terminal to launch the terminal.
+
+# Solution
+
+# VPC with Variables — `datacenter-vpc` (`KKE_vpc`)
+
+This task requires a **two-file** Terraform structure: `variables.tf` holds the
+configuration values, and `main.tf` references them. The VPC name must be stored in a
+variable named exactly `KKE_vpc`.
+
+## `variables.tf`
+
+```hcl
+variable "KKE_vpc" {
+  description = "Name of the VPC"
+  type        = string
+  default     = "datacenter-vpc"
+}
+
+variable "KKE_vpc_cidr" {
+  description = "CIDR block for the VPC"
+  type        = string
+  default     = "10.0.0.0/16"
+}
+```
+
+## `main.tf`
+
+```hcl
+terraform {
+  required_providers {
+    aws = {
+      source  = "hashicorp/aws"
+      version = "~> 6.0"
+    }
+  }
+}
+
+provider "aws" {
+  region = "us-east-1"
+}
+
+resource "aws_vpc" "datacenter_vpc" {
+  cidr_block = var.KKE_vpc_cidr
+
+  tags = {
+    Name = var.KKE_vpc
+  }
+}
+```
+
+## How to run
+
+```bash
+cd /home/bob/terraform
+terraform init
+terraform apply -auto-approve
+```
+
+## How it works
+
+### Splitting config from logic
+
+Terraform loads **every** `.tf` file in the working directory and merges them into one
+configuration, so splitting declarations across files is purely organizational — there
+are no imports to wire up. The convention this task asks for:
+
+- **`variables.tf`** — declares input variables (the "what": names, CIDRs, sizes).
+- **`main.tf`** — declares resources (the "how"), referencing the variables with
+  `var.<name>`.
+
+This separation is standard practice: it centralizes the values people tweak, keeps
+resource blocks generic and reusable, and makes the config easier to parameterize
+later (per-environment `.tfvars`, overrides, etc.).
+
+### The variables
+
+- **`variable "KKE_vpc"`** — holds the VPC name, exactly as required. The `default`
+  of `datacenter-vpc` means no value needs to be passed at apply time; Terraform uses
+  the default.
+- **`variable "KKE_vpc_cidr"`** — holds the CIDR. Putting it here (rather than
+  hardcoding in `main.tf`) satisfies the "configuration values should be stored in
+  variables.tf" note. Its default is the required `10.0.0.0/16`.
+- **`type = string`** constrains each to a string, so Terraform validates the input
+  type at plan time.
+
+### Referencing variables in `main.tf`
+
+- **`cidr_block = var.KKE_vpc_cidr`** — resolves to `10.0.0.0/16`.
+- **`tags = { Name = var.KKE_vpc }`** — resolves the VPC's `Name` tag to
+  `datacenter-vpc`. A VPC has no native name field, so the `Name` tag is what the
+  console and graders read as its name.
+
+The `var.` prefix is how Terraform interpolates a declared variable's value. Because
+both variables have defaults, `terraform apply` runs non-interactively; without
+defaults, Terraform would prompt for the values (or you'd pass `-var` / a `.tfvars`
+file).
+
+## Verify
+
+```bash
+aws ec2 describe-vpcs \
+  --filters Name=tag:Name,Values=datacenter-vpc \
+  --query 'Vpcs[0].{Id:VpcId,Cidr:CidrBlock,Name:Tags[?Key==`Name`]|[0].Value}'
+```
+
+Expected — the VPC ID, `CidrBlock: 10.0.0.0/16`, and `Name: datacenter-vpc`.