Terragrunt for DRY configurations in Terraform - Step-by-Step Execution

Process Flow - Terragrunt for DRY configurations

Write common config in terragrunt.hcl

↓

Reference common config in child modules

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Run terragrunt apply in child module

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Terragrunt merges configs

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Terraform runs with merged config

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Infrastructure deployed with DRY configs

Terragrunt lets you write shared config once and reuse it in many places, avoiding repetition.

Execution Sample

Terraform

terraform {
  source = "../modules/app"
}

include {
  path = find_in_parent_folders()
}

Child terragrunt.hcl references common config from parent to reuse settings.

Process Table

Step	Action	Config Source	Merged Config	Result
1	Terragrunt reads child terragrunt.hcl	Child file	Child config only	Partial config loaded
2	Terragrunt finds parent terragrunt.hcl	Parent file	Parent config only	Common config loaded
3	Terragrunt merges parent and child configs	Parent + Child	Combined config	Full config ready
4	Terragrunt runs terraform with merged config	Merged config	Final config	Terraform applies infrastructure
5	Terraform deploys resources	Final config	N/A	Infrastructure created
6	Execution ends	N/A	N/A	Deployment complete

💡 All configs merged and terraform applied successfully

Status Tracker

Variable	Start	After Step 2	After Step 3	Final
config	{}	{common settings}	{common + child settings}	{merged config}

Key Moments - 2 Insights

Why does Terragrunt look for a parent terragrunt.hcl?

Terragrunt searches parent folders to find shared config to merge with child config, as shown in execution_table step 2 and 3.

What happens if child and parent configs have the same setting?

Child config overrides parent config for that setting during merge (step 3), ensuring specific customization.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does Terragrunt merge parent and child configs?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Check the 'Action' column for merging configs in execution_table row 3.

According to variable_tracker, what is the state of 'config' after step 2?

A {}

B {common + child settings}

C {common settings}

D {merged config}

💡 Hint

Look at the 'After Step 2' column for 'config' in variable_tracker.

If the child config overrides a setting from the parent, which step shows this effect?

A Step 3

B Step 2

C Step 1

D Step 5

💡 Hint

Merging configs and resolving conflicts happens at step 3 in execution_table.

Concept Snapshot

Terragrunt helps avoid repeating config by
sharing common settings in a parent terragrunt.hcl.
Child configs include parent with 'include' block.
Terragrunt merges configs before running Terraform.
Overrides in child config customize behavior.
Run 'terragrunt apply' in child folder to deploy.

Full Transcript

Terragrunt is a tool that helps you keep your Terraform configurations DRY, meaning you don't repeat the same settings in many places. You write common configuration once in a parent terragrunt.hcl file. Then, in child folders, you write terragrunt.hcl files that include the parent config using the 'include' block. When you run 'terragrunt apply' in a child folder, Terragrunt reads the child config, finds the parent config, merges them together, and then runs Terraform with the combined configuration. If the child config has settings that overlap with the parent, the child's settings take priority. This way, you can share common infrastructure settings and customize only what you need in each child folder. The execution table shows these steps clearly, from reading configs to merging and applying infrastructure. The variable tracker shows how the configuration state changes as Terragrunt processes the files. This approach saves time and reduces errors by avoiding duplicated code.