Modules + Output from for_each

Using for_each with modules in Terraform allows you to dynamically create multiple instances of a module and manage their outputs effectively. This is particularly useful for scaling and managing similar resources.

Why Use for_each with Modules?

• Dynamic Resource Creation: Create multiple instances of a module with different configurations.
• Simplified Code: Reduce repetition in your Terraform configuration.
• Centralized Management: Manage similar resources through a single module.

Example: Creating Multiple VPCs

Here's how to use for_each with a module to create multiple VPCs:

Step 1: Define the Module

Create a module for VPC creation in modules/vpc/main.tf:

resource "aws_vpc" "example" {
  cidr_block = var.cidr_block

  tags = {
    Name = var.name
  }
}

variable "cidr_block" {}
variable "name" {}

Step 2: Use the Module with for_each

In your main configuration, use for_each to create multiple VPCs:

module "vpcs" {
  source = "./modules/vpc"

  for_each = {
    vpc1 = { cidr_block = "10.0.0.0/16", name = "VPC1" }
    vpc2 = { cidr_block = "10.1.0.0/16", name = "VPC2" }
  }

  cidr_block = each.value.cidr_block
  name       = each.value.name
}

Step 3: Output the Results

Use outputs to expose information about the created VPCs:

output "vpc_ids" {
  value = { for k, v in module.vpcs : k => v.id }
}

Explanation

• for_each: Iterates through a map of VPC configurations.
• each.value: Accesses the current map value in the iteration.
• output: Dynamically generates a map of VPC IDs.

Best Practices

• Use descriptive keys in your for_each map for better readability.
• Validate input data to ensure it meets your requirements.
• Keep modules reusable by parameterizing them with variables.

By using for_each with modules, you can efficiently manage dynamic resources and outputs in Terraform.