Modules

The Root Module

Every Terraform configuration has at least one module, known as its root module, which consists of the resources defined in the .tf files in the main working directory.

Child Modules

A Terraform module can call another module to include its resources in the configuration.

A module called by another module is referred to as a child module.

Child modules can be called multiple times within the same configuration, and multiple configurations can use the same child module.

module "consul" {
  source  = "hashicorp/consul/aws"
  version = "0.0.5"

  servers = 3
}

Published Modules

Terraform can load modules from the local filesystem, a public registry, or a private registry.

This allows teams to publish reusable modules and consume modules published by others.

The Terraform Registry hosts publicly available modules for common infrastructure patterns.

Terraform downloads a registry module automatically when its source and version are specified in a module block.

Module arguments

Within the block body (between { and }) are the arguments for the module. Module calls use the following kinds of arguments:

• The source argument is mandatory for all modules.
• The version argument is recommended for modules from a registry.
• Most other arguments correspond to input variables defined by the module.
• Terraform defines a few other meta-arguments that can be used with all modules:
  • count - Creates multiple instances of a module from a single module block. See the count page for details.
  • for_each - Creates multiple instances of a module from a single module block.
  • providers - Passes provider configurations to a child module. If not specified, the child module inherits all of the default (un-aliased) provider configurations from the calling module.
  • depends_on - Creates explicit dependencies between the entire module and the listed targets.

Module Sources

The source argument tells Terraform where to find the child module’s source code.

During terraform init, Terraform downloads the source code to local disk so other commands can use it.

The module installer supports several source types:

• local paths - source = "./consul"
• Terraform Registry - source = "hashicorp/consul/aws"
• GitHub - source = "github.com/hashicorp/example", source = "git@github.com:hashicorp/example.git"
• Bitbucket - source = "bitbucket.org/hashicorp/terraform-consul-aws"
• Generic Git, Mercurial repositories - source = "git::https://example.com/vpc.git"", source = "git::ssh://username@example.com/storage.git"
  • Selecting a Revision source = "git::https://example.com/vpc.git?ref=v1.2.0"
• HTTP URLs - source = "https://example.com/vpc-module.zip" The extensions that Terraform recognizes for this special behavior are:
  • zip
  • tar.bz2 and tbz2
  • tar.gz and tgz
  • tar.xz and txz
• S3 buckets - source = "s3::https://s3-eu-west-1.amazonaws.com/examplecorp-terraform-modules/vpc.zip"
• GCS buckets - source = "gcs::https://www.googleapis.com/storage/v1/modules/foomodule.zip"
• Modules in Package Sub-directories - source = hashicorp/consul/aws//modules/consul-cluster, source = "git::https://example.com/network.git//modules/vpc"