Root module concept in Terraform - Step-by-Step Execution

Process Flow - Root module concept

Start Terraform Run

↓

Load Root Module

↓

Parse root main.tf

↓

Load child modules if any

↓

Evaluate variables and outputs

↓

Plan and Apply Infrastructure

↓

End

Terraform starts by loading the root module, which is the main folder with configuration files. It then processes any child modules, variables, and outputs before applying changes.

Execution Sample

Terraform

terraform {
  required_version = ">= 1.0"
}

resource "aws_s3_bucket" "example" {
  bucket = "my-example-bucket"
}

This code defines a root module with a single AWS S3 bucket resource.

Process Table

Step	Action	Module Loaded	Resource Processed	Variables Evaluated	Outputs Evaluated
1	Start Terraform run	root	none	none	none
2	Parse root main.tf	root	none	none	none
3	Process resource aws_s3_bucket.example	root	aws_s3_bucket.example	none	none
4	Evaluate variables (none defined)	root	aws_s3_bucket.example	none	none
5	Evaluate outputs (none defined)	root	aws_s3_bucket.example	none	none
6	Plan infrastructure changes	root	aws_s3_bucket.example	none	none
7	Apply infrastructure changes	root	aws_s3_bucket.example	none	none
8	End Terraform run	root	aws_s3_bucket.example	none	none

💡 Terraform finishes after applying all resources defined in the root module.

Status Tracker

Variable	Start	After Step 4	Final
bucket_name	undefined	undefined	undefined

Key Moments - 3 Insights

Why does Terraform start with the root module?

Terraform always begins with the root module because it is the main folder containing the configuration files that define the infrastructure. This is shown in execution_table step 2 where the root main.tf is parsed first.

What happens if there are no variables defined in the root module?

If no variables are defined, Terraform simply skips variable evaluation as seen in execution_table step 4 where variables are 'none'. This means default or no values are used.

How does Terraform handle child modules in the root module?

Terraform loads child modules after parsing the root module. This is implied in the concept flow where after loading the root module, child modules are loaded before planning and applying.

Visual Quiz - 3 Questions

Look at the execution table, at which step is the aws_s3_bucket resource processed?

A Step 3

B Step 2

C Step 5

D Step 7

💡 Hint

Check the 'Resource Processed' column in the execution_table rows.

According to the variable tracker, what is the value of 'bucket_name' after step 4?

A empty string

B undefined

C my-example-bucket

D null

💡 Hint

Look at the 'After Step 4' column for 'bucket_name' in variable_tracker.

If a child module was added, at which point in the concept flow would it be loaded?

A Before starting Terraform run

B After applying infrastructure

C After loading root module

D After evaluating outputs

💡 Hint

Refer to the concept_flow ASCII diagram where child modules load after root module.

Concept Snapshot

Terraform Root Module:
- The root module is the main folder with Terraform files.
- Terraform starts by loading and parsing the root module.
- It processes resources, variables, and outputs here.
- Child modules are loaded after the root module.
- Terraform plans and applies infrastructure from the root module.

Full Transcript

Terraform uses the root module as the starting point for any infrastructure deployment. The root module is simply the folder where your main Terraform configuration files live. When you run Terraform, it first loads this root module, parses the configuration files like main.tf, and processes any resources defined there. If there are child modules referenced, Terraform loads those next. Then it evaluates variables and outputs before planning and applying the infrastructure changes. This flow ensures Terraform knows exactly what to create or change in your cloud environment starting from the root module.