Challenge - Configure Resources Using Variables and Expressions

Terraform configurations tend to start life hardcoded. A CIDR block is typed directly into a resource, a subnet block gets copy-pasted twice, and the result works fine for exactly one environment. The moment you need a second one, every literal has to be found and changed by hand, and the copies drift apart. Parameterization is what separates a script that deployed something once from a configuration a team can reuse.

Terraform's answer is a small set of language features that work together. Input variables lift values out of resource blocks and give them explicit type constraints. Complex types such as map(object({...})) let a single variable describe a whole collection of similar resources. The for_each meta-argument turns that collection into one resource instance per entry, replacing repeated blocks with a single one. Built-in functions like cidrsubnet() compute values that would otherwise be hand-calculated and error-prone. Output values and for expressions then project what was created into a shape other configurations and operators can consume.

Objectives

By completing this Intermediate challenge, you will be able to:

• Replace hardcoded values with typed input variables
• Model a set of similar resources with a single collection variable and iterate to create them
• Compute subnet CIDRs with a built-in function instead of writing them by hand
• Expose a resource ID and a name-to-ID map as outputs using a for expression

Prerequisites

Before attempting this challenge, you should be comfortable with:

• Writing and editing Terraform configuration files (HCL syntax)
• Terraform input variables and basic types
• The core Terraform workflow (init, plan, apply)
• Basic AWS networking concepts (VPCs and subnets)

Recommended Lab: Introduction to AWS Terraform