Review Project

Let’s explore the generated app folder.

App Modules

Let’s check out the app/modules/example folder.

main.tf

resource "aws_s3_bucket" "this" {
  bucket = var.bucket # If omitted, Terraform will assign a random, unique name.
  tags   = var.tags
}

variables.tf

variable "bucket" {
  description = "The name of the bucket. If omitted, Terraform will assign a random, unique name." # IE: terraform-2020052606510241590000000
  type        = string
  default     = null
}

variable "tags" {
  description = "(Optional) A mapping of tags to assign to the bucket."
  type        = map(string)
  default     = {}
}

You can see that the starter example module creates an s3 bucket.

Stack Modules

Next let’s look at the generated app/stacks/demo that was created:

app/stacks/demo/main.tf

resource "random_pet" "this" {
  length = 2
}

module "bucket" {
  source     = "../../modules/example"
  bucket     = "bucket-${random_pet.this.id}"
  tags       = var.tags
}

You can see that it’s just another terraform module, that will use the app/modules/example module. It uses the random_pet resource to provide a random but friendly name for the s3 bucket.

Modules vs Stacks

Both modules and stacks are terraform modules. The difference is organizational and how they are can be used.

Modules are reusable pieces of code. Generally, it contains non-business specific logic.
Stacks can be used to group together modules. Generally, this is where more business-specific logic can go.

For example, the app1 stack could be designed to use an instance module. Another, app2 stack could use an instance and rds modules.

There are no hard rules. Stacks can be reusable and you provide the tfvars config. It’s up to you. Here are some more Tfvars Location Thoughts.

Next, we’ll deploy the infrastructure.