Format Module Calls and Composition

Formatting Module Blocks

Module blocks define the inputs to child modules. Well-formatted module calls make the data flow between modules clear and easy to trace.

Module Call Examples

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.1.2"

  name = "${local.resource_prefix}-vpc"
  cidr = var.vpc_cidr

  azs             = var.availability_zones
  private_subnets = var.private_subnet_cidrs
  public_subnets  = var.public_subnet_cidrs

  enable_nat_gateway   = true
  single_nat_gateway   = var.environment != "production"
  enable_dns_hostnames = true

  tags = local.common_tags
}

module "eks" {
  source  = "terraform-aws-modules/eks/aws"
  version = "19.16.0"

  cluster_name    = "${local.resource_prefix}-eks"
  cluster_version = var.kubernetes_version

  vpc_id     = module.vpc.vpc_id
  subnet_ids = module.vpc.private_subnets

  cluster_endpoint_public_access = var.environment == "development"

  eks_managed_node_groups = {
    default = {
      min_size       = var.node_min_size
      max_size       = var.node_max_size
      desired_size   = var.node_desired_size
      instance_types = var.node_instance_types
    }
  }

  tags = local.common_tags
}

Local Module Reference

module "lambda_functions" {
  source   = "./modules/lambda"
  for_each = var.lambda_configs

  function_name = each.key
  handler       = each.value.handler
  runtime       = each.value.runtime
  timeout       = each.value.timeout
  memory_size   = each.value.memory_size

  environment_variables = merge(
    local.common_env_vars,
    each.value.env_vars
  )

  tags = local.common_tags
}

Formatting Conventions

• Source and version first: source and version are always the first two attributes
• Grouped inputs: Related inputs are grouped with blank lines between groups
• Aligned equals: All inputs within a group have aligned = signs
• Module references: module.vpc.vpc_id references are kept inline
• for_each modules: When using for_each, it comes right after source/version
• Tags last: The tags attribute is conventionally the last attribute