Keep Your Terragrunt Architecture DRY

Summary

Learn how to use multiple terragrunt configurations to DRY up your architecture.

Highlights

To do this, we will introduce a new env.hcl configuration in each environment:
└── live
├── terragrunt.hcl
├── _env
│ ├── app.hcl
│ ├── mysql.hcl
│ └── vpc.hcl
├── prod
│ ├── env.hcl
│ ├── app
│ │ └── terragrunt.hcl
│ ├── mysql
│ │ └── terragrunt.hcl
│ └── vpc
│ └── terragrunt.hcl
├── qa
│ ├── env.hcl
│ ├── app
│ │ └── terragrunt.hcl
│ ├── mysql
│ │ └── terragrunt.hcl
│ └── vpc
│ └── terragrunt.hcl
└── stage
├── env.hcl
├── app
│ └── terragrunt.hcl
├── mysql
│ └── terragrunt.hcl
└── vpc
└── terragrunt.hcl
The env.hcl configuration will look like the following:
locals {
env = "qa" # this will be prod in the prod folder, and stage in the stage folder.
}
We can then load the env.hcl file in the _env/app.hcl file to load the env string:
locals {

Load the relevant env.hcl file based on where terragrunt was invoked. This works because find_in_parent_folders

always works at the context of the child configuration.

env_vars = read_terragrunt_config(find_in_parent_folders("env.hcl"))
env_name = local.env_vars.locals.env
source_base_url = "github.com//modules.git//app"
}
dependency "vpc" {
config_path = "../vpc"
}
dependency "mysql" {
config_path = "../mysql"
}
inputs = {
env = local.env_name
basename = "example-app-

{local.env_name}" vpc_id = dependency.vpc.outputs.vpc_id subnet_ids = dependency.vpc.outputs.subnet_ids mysql_endpoint = dependency.mysql.outputs.endpoint } With this configuration, `env_vars` is loaded based on which folder is being invoked. For example, when Terragrunt is invoked in the `prod/app/terragrunt.hcl` folder, `prod/env.hcl` is loaded, while `qa/env.hcl` is loaded when Terragrunt is invoked in the `qa/app/terragrunt.hcl` folder. Now we can clean up the child config to eliminate the `env` input variable since that is loaded in the `env.hcl` context: include "root" { path = find_in_parent_folders() } include "env" { path = "

{get_terragrunt_dir()}/../../_env/app.hcl"
expose = true
}

Construct the terraform.source attribute using the source_base_url and custom version v0.2.0

terraform {
source = "${include.env.locals.source_base_url}?ref=v0.2.0"
} ([View Highlight] (https://read.readwise.io/read/01h1mvearm3zw6a5s0sct6b3yq))

Roll out the change to the qa environment first terragrunt run-all plan --terragrunt-modules-that-include _env/app.hcl --terragrunt-working-dir qa terragrunt run-all apply --terragrunt-modules-that-include _env/app.hcl --terragrunt-working-dir qa # If the apply succeeds to qa, move on to the stage environment terragrunt run-all plan --terragrunt-modules-that-include _env/app.hcl --terragrunt-working-dir stage terragrunt run-all apply --terragrunt-modules-that-include _env/app.hcl --terragrunt-working-dir stage # And finally, prod. terragrunt run-all plan --terragrunt-modules-that-include _env/app.hcl --terragrunt-working-dir prod terragrunt run-all apply --terragrunt-modules-that-include _env/app.hcl --terragrunt-working-dir prod ([View Highlight] (https://read.readwise.io/read/01h1mvge4qc50sfzmayq9v4ctz))