terragrunt-nested-configuration

Example of nested configuration in repo with terragrunt stacks organized in tree.

Terragrunt stacks are organized under env/ directory:

env
├── cfg.yaml
├── root.hcl
├── prod
│  ├── cfg.yaml
│  ├── ecr
│  │  ├── cfg.yaml
│  │  └── terragrunt.hcl
│  ├── ecs
│  │  ├── cluster
│  │  │  ├── cfg.yaml
│  │  │  └── terragrunt.hcl
│  │  └── tasks
│  │     ├── cfg.yaml
│  │     └── terragrunt.hcl
│  └── network
│     ├── cfg.yaml
│     └── terragrunt.hcl
└── stg
   ├── cfg.yaml
...

cfg.yaml files are merged. F.e. for stack defined in env/prod/ecs/cluster/terragrunt.hcl, terragrunt will try to read and merge files env/cfg.yaml, env/prod/cfg.yaml, env/prod/ecs/cfg.yaml, env/prod/ecs/cluster/cfg.yaml.

Merging logic is defined in env/root.hcl which should be included into each terragrunt.hcl file with this code:

include "root" {
  path   = find_in_parent_folders("root.hcl")
  expose = true
}

locals {
  cfg = include.root.locals.cfg
}

Note that this example uses merge() function which does not do deep merging, so it's not possible to merge complex configurations. This simple solution is mostly suitable for simple flat key-value configurations.

Demo

$ export TERRAGRUNT_NON_INTERACTIVE=true
$ terragrunt run-all init >/dev/null 2>&1
$ terragrunt run-all apply -auto-approve >/dev/null 2>&1
$ terragrunt --terragrunt-parallelism 1 run-all output 2>/dev/null
====== staging/ecs/cluster
tg_cfg = {
  "aws_account_id" = "234567890123"
  "aws_account_name" = "stg-account"
  "aws_region" = "eu-west-1"
  "environment" = "staging"
  "stack_description" = "AWS ECS cluster"
  "stack_name" = "ecs/cluster"
}
====== production/ecs/cluster
tg_cfg = {
  "aws_account_id" = "123456789012"
  "aws_account_name" = "prod-account"
  "aws_region" = "eu-west-1"
  "environment" = "production"
  "stack_description" = "AWS ECS cluster"
  "stack_name" = "ecs/cluster"
}
====== staging/ecs/tasks
tg_cfg = {
  "aws_account_id" = "234567890123"
  "aws_account_name" = "stg-account"
  "aws_region" = "eu-west-1"
  "environment" = "staging"
  "stack_description" = "AWS ECS cluster tasks"
  "stack_name" = "ecs/tasks"
}
====== staging/network
tg_cfg = {
  "aws_account_id" = "234567890123"
  "aws_account_name" = "stg-account"
  "aws_region" = "eu-west-1"
  "environment" = "staging"
  "stack_description" = "AWS VPC and subnets"
  "stack_name" = "network"
}
====== production/ecr
tg_cfg = {
  "aws_account_id" = "123456789012"
  "aws_account_name" = "prod-account"
  "aws_region" = "eu-west-1"
  "environment" = "production"
  "stack_description" = "AWS ECR private repositories"
  "stack_name" = "ecr"
}
====== production/network
tg_cfg = {
  "aws_account_id" = "123456789012"
  "aws_account_name" = "prod-account"
  "aws_region" = "eu-west-1"
  "environment" = "production"
  "stack_description" = "AWS VPC and subnets"
  "stack_name" = "network"
}
====== production/ecs/tasks
tg_cfg = {
  "aws_account_id" = "123456789012"
  "aws_account_name" = "prod-account"
  "aws_region" = "eu-west-1"
  "environment" = "production"
  "stack_description" = "AWS ECS cluster tasks"
  "stack_name" = "ecs/tasks"
}
====== staging/ecr
tg_cfg = {
  "aws_account_id" = "234567890123"
  "aws_account_name" = "stg-account"
  "aws_region" = "eu-west-1"
  "environment" = "staging"
  "stack_description" = "AWS ECR private repositories"
  "stack_name" = "ecr"
}