Terragrunt

Terragrunt is a thin wrapper for Terraform that provides extra tools for keeping your Terraform configurations DRY, working with multiple Terraform modules, and managing remote state. Check out Terragrunt: how to keep your Terraform code DRY and maintainable for a quick introduction to Terragrunt.

Quick start

1. Install Terraform.

2. Install Terragrunt by going to the Releases Page, downloading the binary for your OS, renaming it to terragrunt, and adding it to your PATH.

   • See the Install Terragrunt docs for other installation options.

3. Go into a folder with your Terraform configurations (.tf files) and create a terragrunt.hcl file that contains the configuration for Terragrunt (Terragrunt configuration uses the exact language, HCL, as Terraform). Here's an example of using Terragrunt to keep your Terraform backend configuration DRY (check out the Use cases section for other types of configuration Terragrunt supports):

   # terragrunt.hcl example
   remote_state {
     backend = "s3"
     config = {
       bucket         = "my-terraform-state"
       key            = "${path_relative_to_include()}/terraform.tfstate"
       region         = "us-east-1"
       encrypt        = true
       dynamodb_table = "my-lock-table"
     }   
   }

4. Now, instead of running terraform directly, run all the standard Terraform commands using terragrunt:

   terragrunt get
   terragrunt plan
   terragrunt apply
   terragrunt output
   terragrunt destroy

   Terragrunt forwards almost all commands, arguments, and options directly to Terraform, using whatever version of Terraform you already have installed. However, based on the settings in your terragrunt.hcl file, Terragrunt can configure remote state, locking, extra arguments, and lots more.

5. Terragrunt is a direct implementation of the ideas expressed in Terraform: Up & Running. Additional background reading that will help explain the motivation for Terragrunt include Terragrunt: how to keep your Terraform code DRY and maintainable, How to create reusable infrastructure with Terraform modules and How to use Terraform as a team.

6. Check out the terragrunt-infrastructure-modules-example and terragrunt-infrastructure-live-example repos for fully-working sample code that demonstrates how to use Terragrunt.

Table of Contents

1. Install Terragrunt
2. Migrating to Terraform 0.12 and Terragrunt 0.19.x
3. Use cases
   1. Keep your Terraform code DRY
   2. Keep your remote state configuration DRY
   3. Keep your CLI flags DRY
   4. Execute Terraform commands on multiple modules at once
   5. Work with multiple AWS accounts
4. Terragrunt details
   1. Inputs
   2. AWS credentials
   3. AWS IAM policies
   4. Built-in Functions
   5. Before and After Hooks
   6. Auto-Init
   7. Auto-Retry
   8. CLI options
   9. Configuration
   10. Clearing the Terragrunt cache
   11. Contributing
   12. Developing Terragrunt
   13. License

Install Terragrunt

Note that third-party Terragrunt packages may not be updated with the latest version, but are often close. Please check your version against the latest available on the Releases Page.

OSX

You can install Terragrunt on OSX using Homebrew: brew install terragrunt.

Linux

You can install Terragrunt on Linux using Linuxbrew: brew install terragrunt.

Manual

You can install Terragrunt manually by going to the Releases Page, downloading the binary for your OS, renaming it to terragrunt, and adding it to your PATH.

Migrating to Terraform 0.12 and Terragrunt 0.19.x

If you were using Terraform <= 0.11.x with Terragrunt <= 0.18.x, and you wish to upgrade to Terraform 0.12.x newer, you'll need to upgrade to Terragrunt 0.19.x or newer. Due to some changes in Terraform 0.12.x, this is a backwards incompatible upgrade that requires some manual migration steps. Check out our Upgrading to Terragrunt 0.19.x Guide for instructions.

Use cases

Terragrunt supports the following use cases:

1. Keep your Terraform code DRY
2. Keep your remote state configuration DRY
3. Keep your CLI flags DRY
4. Execute Terraform commands on multiple modules at once
5. Work with multiple AWS accounts

Keep your Terraform code DRY

• Motivation
• Remote Terraform configurations
• How to use remote configurations
• Achieve DRY Terraform code and immutable infrastructure
• Working locally
• Important gotcha: working with relative file paths
• Using Terragrunt with private Git repos

Motivation

Consider the following file structure, which defines three environments (prod, qa, stage) with the same infrastructure in each one (an app, a MySQL database, and a VPC):

└── live
    ├── prod
    │   ├── app
    │   │   └── main.tf
    │   ├── mysql
    │   │   └── main.tf
    │   └── vpc
    │       └── main.tf
    ├── qa
    │   ├── app
    │   │   └── main.tf
    │   ├── mysql
    │   │   └── main.tf
    │   └── vpc
    │       └── main.tf
    └── stage
        ├── app
        │   └── main.tf
        ├── mysql
        │   └── main.tf
        └── vpc
            └── main.tf

The contents of each environment will be more or less identical, except perhaps for a few settings (e.g. the prod environment may run bigger or more servers). As the size of the infrastructure grows, having to maintain all of this duplicated code between environments becomes more error prone. You can reduce the amount of copy paste using Terraform modules, but even the code to instantiate a module and set up input variables, output variables, providers, and remote state can still create a lot of maintenance overhead.

How can you keep your Terraform code DRY so that you only have to define it once, no matter how many environments you have?

Remote Terraform configurations

Terragrunt has the ability to download remote Terraform configurations. The idea is that you define the Terraform code for your infrastructure just once, in a single repo, called, for example, modules:

└── modules
    ├── app
    │   └── main.tf
    ├── mysql
    │   └── main.tf
    └── vpc
        └── main.tf

This repo contains typical Terraform code, with one difference: anything in your code that should be different between environments should be exposed as an input variable. For example, the app module might expose the following variables:

variable "instance_count" {
  description = "How many servers to run"
}

variable "instance_type" {
  description = "What kind of servers to run (e.g. t2.large)"
}

These variables allow you to run smaller/fewer servers in qa and stage to save money and larger/more servers in prod to ensure availability and scalability.

In a separate repo, called, for example, live, you define the code for all of your environments, which now consists of just one terragrunt.hcl file per component (e.g. app/terragrunt.hcl, mysql/terragrunt.hcl, etc). This gives you the following file layout:

└── live
    ├── prod
    │   ├── app
    │   │   └── terragrunt.hcl
    │   ├── mysql
    │   │   └── terragrunt.hcl
    │   └── vpc
    │       └── terragrunt.hcl
    ├── qa
    │   ├── app
    │   │   └── terragrunt.hcl
    │   ├── mysql
    │   │   └── terragrunt.hcl
    │   └── vpc
    │       └── terragrunt.hcl
    └── stage
        ├── app
        │   └── terragrunt.hcl
        ├── mysql
        │   └── terragrunt.hcl
        └── vpc
            └── terragrunt.hcl

Notice how there are no Terraform configurations (.tf files) in any of the folders. Instead, each terragrunt.hcl file specifies a terraform { ... } block that specifies from where to download the Terraform code, as well as the environment-specific values for the input variables in that Terraform code. For example, stage/app/terragrunt.hcl may look like this:

terraform {
  # Deploy version v0.0.3 in stage
  source = "git::git@github.com:foo/modules.git//app?ref=v0.0.3"
}

inputs = {
  instance_count = 3
  instance_type  = "t2.micro"
}

(Note: the double slash (//) in the source parameter is intentional and required. It's part of Terraform's Git syntax for module sources. Terraform may display a "Terraform initialized in an empty directory" warning, but you can safely ignore it.)

And prod/app/terragrunt.hcl may look like this:

terraform {
  # Deploy version v0.0.1 in prod
  source = "git::git@github.com:foo/modules.git//app?ref=v0.0.1"
}

inputs = {
  instance_count = 10
  instance_type  = "m2.large"
}

You can now deploy the modules in your live repo. For example, to deploy the app module in stage, you would do the following:

cd live/stage/app
terragrunt apply

When Terragrunt finds the terraform block with a source parameter in live/stage/app/terragrunt.hcl file, it will:

1. Download the configurations specified via the source parameter into the --terragrunt-download-dir folder (by default .terragrunt-cache in the working directory, which we recommend adding to .gitignore). This downloading is done by using the same go-getter library Terraform uses, so the source parameter supports the exact same syntax as the module source parameter, including local file paths, Git URLs, and Git URLs with ref parameters (useful for checking out a specific tag, commit, or branch of Git repo). Terragrunt will download all the code in the repo (i.e. the part before the double-slash //) so that relative paths work correctly between modules in that repo.

2. Copy all files from the current working directory into the temporary folder.

3. Execute whatever Terraform command you specified in that temporary folder.

4. Pass any variables defined in the inputs = { ... } block as environment variables (prefixed with TF_VAR_ to your Terraform code. Notice how the inputs block in stage/app/terragrunt.hcl deploys fewer and smaller instances than prod.

Check out the terragrunt-infrastructure-modules-example and terragrunt-infrastructure-live-example repos for fully-working sample code that demonstrates this new folder structure.

Achieve DRY Terraform code and immutable infrastructure

With this new approach, copy/paste between environments is minimized. The terragrunt.hcl files contain solely the source URL of the module to deploy and the inputs to set for that module in the current environment. To create a new environment, you copy an old one and update just the environment-specific inputs in the terragrunt.hcl files, which is about as close to the "essential complexity" of the problem as you can get.

Just as importantly, since the Terraform module code is now defined in a single repo, you can version it (e.g., using Git tags and referencing them using the ref parameter in the source URL, as in the stage/app/terragrunt.hcl and prod/app/terragrunt.hcl examples above), and promote a single, immutable version through each environment (e.g., qa -> stage -> prod). This idea is inspired by Kief Morris' blog post Using Pipelines to Manage Environments with Infrastructure as Code.

Working locally

If you're testing changes to a local copy of the modules repo, you you can use the --terragrunt-source command-line option or the TERRAGRUNT_SOURCE environment variable to override the source parameter. This is useful to point Terragrunt at a local checkout of your code so you can do rapid, iterative, make-a-change-and-rerun development:

cd live/stage/app
terragrunt apply --terragrunt-source ../../../modules//app

(Note: the double slash (//) here too is intentional and required. Terragrunt downloads all the code in the folder before the double-slash into the temporary folder so that relative paths between modules work correctly. Terraform may display a "Terraform initialized in an empty directory" warning, but you can safely ignore it.)

Important gotcha: Terragrunt caching

The first time you set the source parameter to a remote URL, Terragrunt will download the code from that URL into a tmp folder. It will NOT download it again afterwords unless you change that URL. That's because downloading code—and more importantly, reinitializing remote state, redownloading provider plugins, and redownloading modules—can take a long time. To avoid adding 10-90 seconds of overhead to every Terragrunt command, Terragrunt assumes all remote URLs are immutable, and only downloads them once.

Therefore, when working locally, you should use the --terragrunt-source parameter and point it at a local file path as described in the previous section. Terragrunt will copy the local files every time you run it, which is nearly instantaneous, and doesn't require reinitializing everything, so you'll be able to iterate quickly.

If you need to force Terragrunt to redownload something from a remote URL, run Terragrunt with the --terragrunt-source-update flag and it'll delete the tmp folder, download the files from scratch, and reinitialize everything. This can take a while, so avoid it and use --terragrunt-source when you can!

Important gotcha: working with relative file paths

One of the gotchas with downloading Terraform configurations is that when you run terragrunt apply in folder foo, Terraform will actually execute in some temporary folder such as .terragrunt-cache/foo. That means you have to be especially careful with relative file paths, as they will be relative to that temporary folder and not the folder where you ran Terragrunt!

In particular:

• Command line: When using file paths on the command line, such as passing an extra -var-file argument, you should use absolute paths:

  # Use absolute file paths on the CLI!
  terragrunt apply -var-file /foo/bar/extra.tfvars

• Terragrunt configuration: When using file paths directly in your Terragrunt configuration (terragrunt.hcl), such as in an extra_arguments block, you can't use hard-coded absolute file paths, or it won't work on your teammates' computers. Therefore, you should utilize the Terragrunt built-in function get_terragrunt_dir() to use a relative file path:

  terraform {
    source = "git::git@github.com:foo/modules.git//frontend-app?ref=v0.0.3"
  
    extra_arguments "custom_vars" {
      commands = [
        "apply",
        "plan",
        "import",
        "push",
        "refresh"
      ]
  
      # With the get_terragrunt_dir() function, you can use relative paths!
      arguments = [
        "-var-file=${get_terragrunt_dir()}/../common.tfvars",
        "-var-file=example.tfvars"
      ]
    }
  }

  See the get_terragrunt_dir() documentation for more details.

Using Terragrunt with private Git repos

The easiest way to use Terragrunt with private Git repos is to use SSH authentication. Configure your Git account so you can use it with SSH (see the guide for GitHub here) and use the SSH URL for your repo, prepended with git::ssh://:

terraform {
  source = "git::ssh://git@github.com/foo/modules.git//path/to/module?ref=v0.0.1"
}

Look up the Git repo for your repository to find the proper format.

Note: In automated pipelines, you may need to run the following command for your Git repository prior to calling terragrunt to ensure that the ssh host is registered locally, e.g.:

$ ssh -T -oStrictHostKeyChecking=accept-new git@github.com || true

Keep your remote state configuration DRY

• Motivation
• Filling in remote state settings with Terragrunt
• Create remote state and locking resources automatically

Motivation

Terraform supports remote state storage via a variety of backends that you normally configure in your .tf files as follows:

terraform {
  backend "s3" {
    bucket         = "my-terraform-state"
    key            = "frontend-app/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "my-lock-table"
  }
}

Unfortunately, the backend configuration does not support expressions, variables, or functions. This makes it hard to keep your code DRY if you have multiple Terraform modules. For example, consider the following folder structure, which uses different Terraform modules to deploy a backend app, frontend app, MySQL database, and a VPC:

├── backend-app
│   └── main.tf
├── frontend-app
│   └── main.tf
├── mysql
│   └── main.tf
└── vpc
    └── main.tf

To use remote state with each of these modules, you would have to copy/paste the exact same backend configuration into each of the main.tf files. The only thing that would differ between the configurations would be the key parameter: e.g., the key for mysql/main.tf might be mysql/terraform.tfstate and the key for frontend-app/main.tf might be frontend-app/terraform.tfstate.

To keep your remote state configuration DRY, you can use Terragrunt. You still have to specify the backend you want to use in each module, but instead of copying and pasting the configuration settings over and over again into each main.tf file, you can leave them blank (this is known as partial configuration):

terraform {
  # The configuration for this backend will be filled in by Terragrunt
  backend "s3" {}
}

Filling in remote state settings with Terragrunt

To fill in the settings via Terragrunt, create a terragrunt.hcl file in the root folder, plus one terragrunt.hcl file in each of the Terraform modules:

├── terragrunt.hcl
├── backend-app
│   ├── main.tf
│   └── terragrunt.hcl
├── frontend-app
│   ├── main.tf
│   └── terragrunt.hcl
├── mysql
│   ├── main.tf
│   └── terragrunt.hcl
└── vpc
    ├── main.tf
    └── terragrunt.hcl

In your root terragrunt.hcl file, you can define your entire remote state configuration just once in a remote_state block (which supports all the same backend types as Terraform), as follows:

remote_state {
  backend = "s3"
  config = {
    bucket         = "my-terraform-state"
    key            = "${path_relative_to_include()}/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "my-lock-table"
  }
}

In each of the child terragrunt.hcl files, such as mysql/terragrunt.hcl, you can tell Terragrunt to automatically include all the settings from the root terragrunt.hcl file as follows:

include {
  path = find_in_parent_folders()
}

The include block tells Terragrunt to use the exact same Terragrunt configuration from the terragrunt.hcl file specified via the path parameter. It behaves exactly as if you had copy/pasted the Terraform configuration from the included file remote_state configuration into mysql/terragrunt.hcl, but this approach is much easier to maintain!

The next time you run terragrunt, it will automatically configure all the settings in the remote_state.config block, if they aren't configured already, by calling terraform init.

The terragrunt.hcl files above use two Terragrunt built-in functions:

• find_in_parent_folders(): This function returns the path to the first terragrunt.hcl file it finds in the parent folders above the current terragrunt.hcl file. In the example above, the call to find_in_parent_folders() in mysql/terragrunt.hcl will return ../terragrunt.hcl. This way, you don't have to hard code the path parameter in every module.

• path_relative_to_include(): This function returns the relative path between the current terragrunt.hcl file and the path specified in its include block. We typically use this in a root terragrunt.hcl file so that each Terraform child module stores its Terraform state at a different key. For example, the mysql module will have its key parameter resolve to mysql/terraform.tfstate and the frontend-app module will have its key parameter resolve to frontend-app/terraform.tfstate.

See the Built-in Functions docs for more info.

Check out the terragrunt-infrastructure-modules-example and terragrunt-infrastructure-live-example repos for fully-working sample code that demonstrates how to use Terragrunt to manage remote state.

Rules for merging parent and child configurations

The child .hcl file's terraform settings will be merged into the parent file's terraform settings as follows:

• If an extra_arguments block in the child has the same name as an extra_arguments block in the parent, then the child's block will override the parent's.
  • Specifying an empty extra_arguments block in a child with the same name will effectively remove the parent's block.
• If an extra_arguments block in the child has a different name than extra_arguments blocks in the parent, then both the parent and child's extra_arguments will be effective.
  • The child's extra_arguments will be placed after the parent's extra_arguments on the terraform command line.
  • Therefore, if a child's and parent's extra_arguments include .tfvars files with the same variable defined, the value from the .tfvars file from the child's extra_arguments will be used by terraform.
• If a before_hook or after_hook block in the child has the same name as the hook block in the parent, then the child's block will override the parent's.
  • Specifying an empty hook block in a child with the same name will effectively remove the parent's block.
• If a before_hook or after_hook block in the child has a different name than hook blocks in the parent, then both the parent and child's hook blocks will be effective.
• The source field in the child will override source field in the parent

Other settings in the child .hcl file override the respective settings in the parent.

Create remote state and locking resources automatically

When you run terragrunt with remote_state configuration, it will automatically create the following resources if they don't already exist:

• S3 bucket: If you are using the S3 backend for remote state storage and the bucket you specify in remote_state.config doesn't already exist, Terragrunt will create it automatically, with versioning, server-side encryption, and access logging enabled.

  In addition, you can let terragrunt tag the bucket with custom tags that you specify in remote_state.config.s3_bucket_tags.

• DynamoDB table: If you are using the S3 backend for remote state storage and you specify a dynamodb_table (a DynamoDB table used for locking) in remote_state.config, if that table doesn't already exist, Terragrunt will create it automatically, with server-side encryption enabled, including a primary key called LockID.

  In addition, you can let terragrunt tag the DynamoDB table with custom tags that you specify in remote_state.config.dynamodb_table_tags.

• GCS bucket: If you are using the GCS backend for remote state storage and the bucket you specify in remote_state.config doesn't already exist, Terragrunt will create it automatically, with versioning enabled. For this to work correctly you must also specify project and location keys in remote_state.config, so terragrunt knows where to create the bucket.

  We also strongly recommend you enable Cloud Audit Logs to audit and track API operations performed against the state bucket.

  In addition, you can let terragrunt label the bucket with custom labels that you specify in remote_state.config.gcs_bucket_labels.

Note: If you specify a profile key in remote_state.config, Terragrunt will automatically use this AWS profile when creating the S3 bucket or DynamoDB table.

Note: You can disable automatic remote state initialization by setting remote_state.disable_init, this will skip the automatic creation of remote state resources and will execute terraform init passing the backend=false option. This can be handy when running commands such as validate-all as part of a CI process where you do not want to initialize remote state.

The following example demonstrates using an environment variable to configure this option:

remote_state {
  # ...

  disable_init = tobool(get_env("TERRAGRUNT_DISABLE_INIT", "false"))
}

S3-specific remote state settings

For the s3 backend, the following config options can be used for S3-compatible object stores, as necessary:

remote_state {
  # ...

  skip_bucket_versioning         = true # use only if the object store does not support versioning
  skip_bucket_ssencryption       = true # use only if non-encrypted Terraform State is required and/or the object store does not support server-side encryption
  skip_bucket_accesslogging      = true # use only if the cost for the extra object space is undesirable or the object store does not support access logging
  enable_lock_table_ssencryption = true # use only if non-encrypted DynamoDB Lock Table for the Terraform State is required and/or the NoSQL database service does not support server-side encryption

  shared_credentials_file     = "/path/to/credentials/file"
  skip_credentials_validation = true
  skip_metadata_api_check     = true
  force_path_style            = true
}

If you experience an error for any of these configurations, confirm you are using Terraform v0.11.2 or greater.

Further, the config options s3_bucket_tags, dynamodb_table_tags, skip_bucket_versioning, skip_bucket_ssencryption, skip_bucket_accesslogging, and enable_lock_table_ssencryption are only valid for backend s3. They are used by terragrunt and are not passed on to terraform. See section Create remote state and locking resources automatically.

GCS-specific remote state settings

For the gcs backend, the following config options can be used for GCS-compatible object stores, as necessary:

remote_state {
 # ...

 skip_bucket_versioning = true # use only if the object store does not support versioning

 encryption_key = "GOOGLE_ENCRYPTION_KEY"
}

If you experience an error for any of these configurations, confirm you are using Terraform v0.12.0 or greater.

Further, the config options gcs_bucket_labels and skip_bucket_versioning are only valid for the backend gcs. They are used by terragrunt and are not passed on to terraform. See section Create remote state and locking resources automatically.

Keep your CLI flags DRY

• Motivation
• Multiple extra_arguments blocks
• extra_arguments for init
• Required and optional var-files
• Handling whitespace

Motivation

Sometimes you may need to pass extra CLI arguments every time you run certain terraform commands. For example, you may want to set the lock-timeout setting to 20 minutes for all commands that may modify remote state so that Terraform will keep trying to acquire a lock for up to 20 minutes if someone else already has the lock rather than immediately exiting with an error.

You can configure Terragrunt to pass specific CLI arguments for specific commands using an extra_arguments block in your terragrunt.hcl file:

terraform {
  # Force Terraform to keep trying to acquire a lock for
  # up to 20 minutes if someone else already has the lock
  extra_arguments "retry_lock" {
    commands = [
      "init",
      "apply",
      "refresh",
      "import",
      "plan",
      "taint",
      "untaint"
    ]

    arguments = [
      "-lock-timeout=20m"
    ]

    env_vars = {
      TF_VAR_var_from_environment = "value"
    }
  }
}

Each extra_arguments block includes an arbitrary name (in the example above, retry_lock), a list of commands to which the extra arguments should be added, and a list of arguments or required_var_files or optional_var_files to add. You can also pass custom environment variables using env_vars block, which stores environment variables in key value pairs. With the configuration above, when you run terragrunt apply, Terragrunt will call Terraform as follows:

$ terragrunt apply

terraform apply -lock-timeout=20m

You can even use built-in functions such as get_terraform_commands_that_need_locking to automatically populate the lsit of Terraform commands that need locking:

terraform {
  # Force Terraform to keep trying to acquire a lock for up to 20 minutes if someone else already has the lock
  extra_arguments "retry_lock" {
    commands  = get_terraform_commands_that_need_locking()
    arguments = ["-lock-timeout=20m"]
  }
}

Multiple extra_arguments blocks

You can specify one or more extra_arguments blocks. The arguments in each block will be applied any time you call terragrunt with one of the commands in the commands list. If more than one extra_arguments block matches a command, the arguments will be added in the order of appearance in the configuration. For example, in addition to lock settings, you may also want to pass custom -var-file arguments to several commands:

terraform {
  # Force Terraform to keep trying to acquire a lock for
  # up to 20 minutes if someone else already has the lock
  extra_arguments "retry_lock" {
    commands  = get_terraform_commands_that_need_locking()
    arguments = ["-lock-timeout=20m"]
  }

  # Pass custom var files to Terraform
  extra_arguments "custom_vars" {
    commands = [
      "apply",
      "plan",
      "import",
      "push",
      "refresh"
    ]

    arguments = [
      "-var", "foo=bar",
      "-var", "region=us-west-1"
    ]
  }
}

With the configuration above, when you run terragrunt apply, Terragrunt will call Terraform as follows:

$ terragrunt apply

terraform apply -lock-timeout=20m -var foo=bar -var region=us-west-1

extra_arguments for init

Extra arguments for the init command have some additional behavior and constraints.

In addition to being appended to the terraform init command that is run when you explicitly run terragrunt init, extra_arguments for init will also be appended to the init commands that are automatically run during other commands (see Auto-Init).

You must not specify the -from-module option (aka. the SOURCE argument for terraform < 0.10.0) or the DIR argument in the extra_arguments for init. This option and argument will be provided automatically by terragrunt.

Here's an example of configuring extra_arguments for init in an environment in which terraform plugins are manually installed, rather than relying on terraform to automatically download them.

terraform {
  # ...

  extra_arguments "init_args" {
    commands = [
      "init"
    ]

    arguments = [
      "-get-plugins=false",
      "-plugin-dir=/my/terraform/plugin/dir",
    ]
  }
}

Required and optional var-files

One common usage of extra_arguments is to include tfvars files. Instead of using arguments, it is simpler to use either required_var_files or optional_var_files. Both options require only to provide the list of file to include. The only difference is that required_var_files will add the extra argument -var-file=<your file> for each file specified and if they don't exist, exit with an error. optional_var_files, on the other hand, will skip over files that don't exists. This allows many conditional configurations based on environment variables as you can see in the following example:

/my/tf
├── terragrunt.hcl
├── prod.tfvars
├── us-west-2.tfvars
├── backend-app
│   ├── main.tf
│   ├── dev.tfvars
│   └── terragrunt.hcl
├── frontend-app
│   ├── main.tf
│   ├── us-east-1.tfvars
│   └── terragrunt.hcl

terraform {
  extra_arguments "conditional_vars" {
    commands = [
      "apply",
      "plan",
      "import",
      "push",
      "refresh"
    ]

    required_var_files = [
      "${get_parent_terragrunt_dir()}/terraform.tfvars"
    ]

    optional_var_files = [
      "${get_parent_terragrunt_dir()}/${get_env("TF_VAR_env", "dev")}.tfvars",
      "${get_parent_terragrunt_dir()}/${get_env("TF_VAR_region", "us-east-1")}.tfvars",
      "${get_terragrunt_dir()}/${get_env("TF_VAR_env", "dev")}.tfvars",
      "${get_terragrunt_dir()}/${get_env("TF_VAR_region", "us-east-1")}.tfvars"
    ]
  }

See the get_terragrunt_dir() and get_parent_terragrunt_dir() documentation for more details.

With the configuration above, when you run terragrunt apply-all, Terragrunt will call Terraform as follows:

$ terragrunt apply-all
[backend-app]  terraform apply -var-file=/my/tf/terraform.tfvars -var-file=/my/tf/backend-app/dev.tfvars
[frontend-app] terraform apply -var-file=/my/tf/terraform.tfvars -var-file=/my/tf/frontend-app/us-east-1.tfvars

$ TF_VAR_env=prod terragrunt apply-all
[backend-app]  terraform apply -var-file=/my/tf/terraform.tfvars -var-file=/my/tf/prod.tfvars
[frontend-app] terraform apply -var-file=/my/tf/terraform.tfvars -var-file=/my/tf/prod.tfvars -var-file=/my/tf/frontend-app/us-east-1.tfvars

$ TF_VAR_env=prod TF_VAR_region=us-west-2 terragrunt apply-all
[backend-app]  terraform apply -var-file=/my/tf/terraform.tfvars -var-file=/my/tf/prod.tfvars -var-file=/my/tf/us-west-2.tfvars
[frontend-app] terraform apply -var-file=/my/tf/terraform.tfvars -var-file=/my/tf/prod.tfvars -var-file=/my/tf/us-west-2.tfvars

Handling whitespace

The list of arguments cannot include whitespaces, so if you need to pass command line arguments that include spaces (e.g. -var bucket=example.bucket.name), then each of the arguments will need to be a separate item in the arguments list:

terraform {
  extra_arguments "bucket" {
    commands = [
      "apply",
      "plan",
      "import",
      "push",
      "refresh"
    ]
    
    arguments = [
      "-var", "bucket=example.bucket.name",
    ]
  }
}

With the configuration above, when you run terragrunt apply, Terragrunt will call Terraform as follows:

$ terragrunt apply

terraform apply -var bucket=example.bucket.name

Execute Terraform commands on multiple modules at once

• Motivation
• The apply-all, destroy-all, output-all and plan-all commands
• Dependencies between modules
• Testing multiple modules locally

Motivation

Let's say your infrastructure is defined across multiple Terraform modules:

root
├── backend-app
│   └── main.tf
├── frontend-app
│   └── main.tf
├── mysql
│   └── main.tf
├── redis
│   └── main.tf
└── vpc
    └── main.tf

There is one module to deploy a frontend-app, another to deploy a backend-app, another for the MySQL database, and so on. To deploy such an environment, you'd have to manually run terraform apply in each of the subfolder, wait for it to complete, and then run terraform apply in the next subfolder. How do you avoid this tedious and time-consuming process?

The apply-all, destroy-all, output-all and plan-all commands

To be able to deploy multiple Terraform modules in a single command, add a terragrunt.hcl file to each module:

root
├── backend-app
│   ├── main.tf
│   └── terragrunt.hcl
├── frontend-app
│   ├── main.tf
│   └── terragrunt.hcl
├── mysql
│   ├── main.tf
│   └── terragrunt.hcl
├── redis
│   ├── main.tf
│   └── terragrunt.hcl
└── vpc
    ├── main.tf
    └── terragrunt.hcl

Now you can go into the root folder and deploy all the modules within it by using the apply-all command:

cd root
terragrunt apply-all

When you run this command, Terragrunt will recursively look through all the subfolders of the current working directory, find all folders with a terragrunt.hcl file, and run terragrunt apply in each of those folders concurrently.

Similarly, to undeploy all the Terraform modules, you can use the destroy-all command:

cd root
terragrunt destroy-all

To see the currently applied outputs of all of the subfolders, you can use the output-all command:

cd root
terragrunt output-all

Finally, if you make some changes to your project, you could evaluate the impact by using plan-all command:

Note: It is important to realize that you could get errors running plan-all if you have dependencies between your projects and some of those dependencies haven't been applied yet.

Ex: If module A depends on module B and module B hasn't been applied yet, then plan-all will show the plan for B, but exit with an error when trying to show the plan for A.

cd root
terragrunt plan-all

If your modules have dependencies between them—for example, you can't deploy the backend-app until MySQL and redis are deployed—you'll need to express those dependencies in your Terragrunt configuration as explained in the next section.

Dependencies between modules

Consider the following file structure:

root
├── backend-app
│   ├── main.tf
│   └── terragrunt.hcl
├── frontend-app
│   ├── main.tf
│   └── terragrunt.hcl
├── mysql
│   ├── main.tf
│   └── terragrunt.hcl
├── redis
│   ├── main.tf
│   └── terragrunt.hcl
└── vpc
    ├── main.tf
    └── terragrunt.hcl

Let's assume you have the following dependencies between Terraform modules:

• backend-app depends on mysql, redis, and vpc
• frontend-app depends on backend-app and vpc
• mysql depends on vpc
• redis depends on vpc
• vpc has no dependencies

You can express these dependencies in your terragrunt.hcl config files using a dependencies block. For example, in backend-app/terragrunt.hcl you would specify:

dependencies {
  paths = ["../vpc", "../mysql", "../redis"]
}

Similarly, in frontend-app/terragrunt.hcl, you would specify:

dependencies {
  paths = ["../vpc", "../backend-app"]
}

Once you've specified the dependencies in each terragrunt.hcl file, when you run the terragrunt apply-all or terragrunt destroy-all, Terragrunt will ensure that the dependencies are applied or destroyed, respectively, in the correct order. For the example at the start of this section, the order for the apply-all command would be:

1. Deploy the VPC
2. Deploy MySQL and Redis in parallel
3. Deploy the backend-app
4. Deploy the frontend-app

If any of the modules fail to deploy, then Terragrunt will not attempt to deploy the modules that depend on them. Once you've fixed the error, it's usually safe to re-run the apply-all or destroy-all command again, since it'll be a no-op for the modules that already deployed successfully, and should only affect the ones that had an error the last time around.

To check all of your dependencies and validate the code in them, you can use the validate-all command.

Testing multiple modules locally

If you are using Terragrunt to configure remote Terraform configurations and all of your modules have the source parameter set to a Git URL, but you want to test with a local checkout of the code, you can use the --terragrunt-source parameter:

cd root
terragrunt plan-all --terragrunt-source /source/modules

If you set the --terragrunt-source parameter, the xxx-all commands will assume that parameter is pointing to a folder on your local file system that has a local checkout of all of your Terraform modules. For each module that is being processed via a xxx-all command, Terragrunt will read in the source parameter in that module's terragrunt.hcl file, parse out the path (the portion after the double-slash), and append the path to the --terragrunt-source parameter to create the final local path for that module.

For example, consider the following terragrunt.hcl file:

terraform {
  source = "git::git@github.com:acme/infrastructure-modules.git//networking/vpc?ref=v0.0.1"
}

If you run terragrunt apply-all --terragrunt-source /source/infrastructure-modules, then the local path Terragrunt will compute for the module above will be /source/infrastructure-modules//networking/vpc.

Work with multiple AWS accounts

Motivation

The most secure way to manage infrastructure in AWS is to use multiple AWS accounts. You define all your IAM users in one account (e.g., the "security" account) and deploy all of your infrastructure into a number of other accounts (e.g., the "dev", "stage", and "prod" accounts). To access those accounts, you login to the security account and assume an IAM role in the other accounts.

There are a few ways to assume IAM roles when using AWS CLI tools, such as Terraform:

1. One option is to create a named profile, each with a different role_arn parameter. You then tell Terraform which profile to use via the AWS_PROFILE environment variable. The downside to using profiles is that you have to store your AWS credentials in plaintext on your hard drive.

2. Another option is to use environment variables and the AWS CLI. You first set the credentials for the security account (the one where your IAM users are defined) as the environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY and run aws sts assume-role --role-arn <ROLE>. This gives you back a blob of JSON that contains new AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY values you can set as environment variables to allow Terraform to use that role. The advantage of this approach is that you can store your AWS credentials in a secret store and never write them to disk in plaintext. The disadvantage is that assuming an IAM role requires several tedious steps. Worse yet, the credentials you get back from the assume-role command are only good for up to 1 hour, so you have to repeat this process often.

3. A final option is to modify your AWS provider with the assume_role configuration and your S3 backend with the role_arn parameter. You can then set the credentials for the security account (the one where your IAM users are defined) as the environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY and when you run terraform apply or terragrunt apply, Terraform/Terragrunt will assume the IAM role you specify automatically. The advantage of this approach is that you can store your AWS credentials in a secret store and never write them to disk in plaintext, and you get fresh credentials on every run of apply, without the complexity of calling assume-role. The disadvantage is that you have to modify all your Terraform / Terragrunt code to set the role_arn param and your Terraform backend configuration will change (and prompt you to manually confirm the update!) every time you change the IAM role you're using.

To avoid these frustrating trade-offs, you can configure Terragrunt to assume an IAM role for you, as described next.

Configuring Terragrunt to assume an IAM role

To tell Terragrunt to assume an IAM role, just set the --terragrunt-iam-role command line argument:

terragrunt apply --terragrunt-iam-role "arn:aws:iam::ACCOUNT_ID:role/ROLE_NAME"

Alternatively, you can set the TERRAGRUNT_IAM_ROLE environment variable:

export TERRAGRUNT_IAM_ROLE="arn:aws:iam::ACCOUNT_ID:role/ROLE_NAME"
terragrunt apply

Additionally, you can specify an iam_role property in the terragrunt config:

iam_role = "arn:aws:iam::ACCOUNT_ID:role/ROLE_NAME"

Terragrunt will resolve the value of the option by first looking for the cli argument, then looking for the environment variable, then defaulting to the value specified in the config file.

Terragrunt will call the sts assume-role API on your behalf and expose the credentials it gets back as environment variables when running Terraform. The advantage of this approach is that you can store your AWS credentials in a secret store and never write them to disk in plaintext, you get fresh credentials on every run of Terragrunt, without the complexity of calling assume-role yourself, and you don't have to modify your Terraform code or backend configuration at all.

Terragrunt details

This section contains detailed documentation for the following aspects of Terragrunt:

1. Inputs
2. AWS credentials
3. AWS IAM policies
4. Built-in Functions
5. Before & After Hooks
6. Auto-Init
7. CLI options
8. Configuration
9. Migrating from Terragrunt v0.11.x and Terraform 0.8.x and older
10. Clearing the Terragrunt cache
11. Contributing
12. Developing Terragrunt
13. License

Inputs

You can set values for your module's input parameters by specifying an inputs block in terragrunt.hcl:

inputs = {
  instance_type  = "t2.micro"
  instance_count = 10
  
  tags = {
    Name = "example-app"
  }
}

Whenever you run a Terragrunt command, Terragrunt will set any inputs you pass in as environment variables. For example, with the terragrunt.hcl file above, running terragrunt apply is roughly equivalent to:

$ terragrunt apply

# Roughly equivalent to:

TF_VAR_instance_type="t2.micro" \
TF_VAR_instance_count=10 \
TF_VAR_tags='{"Name":"example-app"}' \
terraform apply

Note that Terragrunt will respect any TF_VAR_xxx variables you've manually set in your environment, ensuring that anything in inputs will NOT be override anything you've already set in your environment.

AWS credentials

Terragrunt uses the official AWS SDK for Go, which means that it will automatically load credentials using the AWS standard approach. If you need help configuring your credentials, please refer to the Terraform docs.

AWS IAM policies

Your AWS user must have an IAM policy which grants permissions for interacting with DynamoDB and S3. Terragrunt will automatically create the configured DynamoDB tables and S3 buckets for storing remote state if they do not already exist.

The following is an example IAM policy for use with Terragrunt. The policy grants the following permissions:

• all DynamoDB permissions in all regions for tables used by Terragrunt
• all S3 permissions for buckets used by Terragrunt

Before using this policy, make sure to replace 1234567890 with your AWS account id and terragrunt* with your organization's naming convention for AWS resources for Terraform remote state.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowAllDynamoDBActionsOnAllTerragruntTables",
            "Effect": "Allow",
            "Action": "dynamodb:*",
            "Resource": [
                "arn:aws:dynamodb:*:1234567890:table/terragrunt*"
            ]
        },
        {
            "Sid": "AllowAllS3ActionsOnTerragruntBuckets",
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": [
                "arn:aws:s3:::terragrunt*",
                "arn:aws:s3:::terragrunt*/*"
            ]
        }
    ]
}

For a more minimal policy, for example when using a single bucket and DynamoDB table for multiple Terragrunt users, you can use the following. Be sure to replace BUCKET_NAME and TABLE_NAME with the S3 bucket name and DynamoDB table name respectively.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowCreateAndListS3ActionsOnSpecifiedTerragruntBucket",
            "Effect": "Allow",
            "Action": [
                "s3:ListBucket",
                "s3:GetBucketVersioning",
                "s3:CreateBucket"
            ],
            "Resource": "arn:aws:s3:::BUCKET_NAME"
        },
        {
            "Sid": "AllowGetAndPutS3ActionsOnSpecifiedTerragruntBucketPath",
            "Effect": "Allow",
            "Action": [
                "s3:PutObject",
                "s3:GetObject"
            ],
            "Resource": "arn:aws:s3:::BUCKET_NAME/some/path/here"
        },
        {
            "Sid": "AllowCreateAndUpdateDynamoDBActionsOnSpecifiedTerragruntTable",
            "Effect": "Allow",
            "Action": [
                "dynamodb:PutItem",
                "dynamodb:GetItem",
                "dynamodb:DescribeTable",
                "dynamodb:DeleteItem",
                "dynamodb:CreateTable"
            ],
            "Resource": "arn:aws:dynamodb:*:*:table/TABLE_NAME"
        }
    ]
}

When the above is applied to an IAM user it will restrict them to creating the DynamoDB table if it doesn't already exist and allow updating records for state locking, and for the S3 bucket will allow creating the bucket if it doesn't already exist and only write files to the specified path.

Built-in Functions

Terragrunt allows you to use built-in functions anywhere in terragrunt.hcl, just like Terraform! The functions currently available are:

• All Terraform built-in functions
• find_in_parent_folders()
• path_relative_to_include()
• path_relative_from_include()
• get_env(NAME, DEFAULT)
• get_terragrunt_dir()
• get_parent_terragrunt_dir()
• get_terraform_commands_that_need_vars()
• get_terraform_commands_that_need_input()
• get_terraform_commands_that_need_locking()
• get_terraform_commands_that_need_parallelism()
• get_aws_account_id()
• run_cmd()

Terraform built-in functions

All Terraform built-in functions are supported in Terragrunt config files:

terraform {
  source = "../modules/${basename(get_terragrunt_dir())}"
}

remote_state {
  backend = "s3"
  config = {
    bucket = trimspace("   my-terraform-bucket     ")
    region = join("-", ["us", "east", "1"])
    key    = format("%s/terraform.tfstate", path_relative_to_include())
  }
}

Note: Any file* functions (file, fileexists, filebase64, etc) are relative to the directory containing the terragrunt.hcl file they're used in.

Given the following structure:

└── terragrunt
  └── common.tfvars
  ├── assets
  |  └── mysql
  |     └── assets.txt
  └── terragrunt.hcl

Then assets.txt could be read with the following function call:

file("assets/mysql/assets.txt")

find_in_parent_folders

find_in_parent_folders() searches up the directory tree from the current terragrunt.hcl file and returns the relative path to the first terragrunt.hcl in a parent folder or exit with an error if no such file is found. This is primarily useful in an include block to automatically find the path to a parent terragrunt.hcl file:

include {
  path = find_in_parent_folders()
}

The function takes an optional name parameter that allows you to specify a different filename to search for:

include {
  path = find_in_parent_folders("some-other-file-name.hcl")
}

You can also pass an optional second fallback parameter which causes the function to return the fallback value (instead of exiting with an error) if the file in the name parameter cannot be found:

include {
  path = find_in_parent_folders("some-other-file-name.tfvars", "fallback.tfvars")
}

path_relative_to_include

path_relative_to_include() returns the relative path between the current terragrunt.hcl file and the path specified in its include block. For example, consider the following folder structure:

├── terragrunt.hcl
└── prod
    └── mysql
        └── terragrunt.hcl
└── stage
    └── mysql
        └── terragrunt.hcl

Imagine prod/mysql/terragrunt.hcl and stage/mysql/terragrunt.hcl include all settings from the root terragrunt.hcl file:

include {
  path = find_in_parent_folders()
}

The root terragrunt.hcl can use the path_relative_to_include() in its remote_state configuration to ensure each child stores its remote state at a different key:

remote_state {
  backend = "s3"
  config = {
    bucket = "my-terraform-bucket"
    region = "us-east-1"
    key    = "${path_relative_to_include()}/terraform.tfstate"
  }
}

The resulting key will be prod/mysql/terraform.tfstate for the prod mysql module and stage/mysql/terraform.tfstate for the stage mysql module.

path_relative_from_include

path_relative_from_include() returns the relative path between the path specified in its include block and the current terragrunt.hcl file (it is the counterpart of path_relative_to_include()). For example, consider the following folder structure:

├── sources
|  ├── mysql
|  |  └── *.tf
|  └── secrets
|     └── mysql
|         └── *.tf
└── terragrunt
  └── common.tfvars
  ├── mysql
  |  └── terragrunt.hcl
  ├── secrets
  |  └── mysql
  |     └── terragrunt.hcl
  └── terragrunt.hcl

Imagine terragrunt/mysql/terragrunt.hcl and terragrunt/secrets/mysql/terragrunt.hcl include all settings from the root terragrunt.hcl file:

include {
  path = find_in_parent_folders()
}

The root terragrunt.hcl can use the path_relative_from_include() in combination with path_relative_to_include() in its source configuration to retrieve the relative terraform source code from the terragrunt configuration file:

terraform {
  source = "${path_relative_from_include()}/../sources//${path_relative_to_include()}"
}

The resulting source will be ../../sources//mysql for mysql module and ../../../sources//secrets/mysql for secrets/mysql module.

Another use case would be to add extra argument to include the common.tfvars file for all subdirectories:

  terraform {
    extra_arguments "common_var" {
      commands = [
        "apply",
        "plan",
        "import",
        "push",
        "refresh"
      ]

      arguments = [
        "-var-file=${get_terragrunt_dir()}/${path_relative_from_include()}/common.tfvars",
      ]
    }
  }

This allows proper retrieval of the common.tfvars from whatever the level of subdirectories we have.

get_env

get_env(NAME, DEFAULT) returns the value of the environment variable named NAME or DEFAULT if that environment variable is not set. Example:

remote_state {
  backend = "s3"
  config = {
    bucket = get_env("BUCKET", "my-terraform-bucket")
  }
}

Note that Terraform will read environment variables that start with the prefix TF_VAR_, so one way to share a variable named foo between Terraform and Terragrunt is to set its value as the environment variable TF_VAR_foo and to read that value in using this get_env() built-in function.

get_terragrunt_dir

get_terragrunt_dir() returns the directory where the Terragrunt configuration file (by default terragrunt.hcl) lives. This is useful when you need to use relative paths with remote Terraform configurations and you want those paths relative to your Terragrunt configuration file and not relative to the temporary directory where Terragrunt downloads the code.

For example, imagine you have the following file structure:

/terraform-code
├── common.tfvars
├── frontend-app
│   └── terragrunt.hcl

Inside of /terraform-code/frontend-app/terragrunt.hcl you might try to write code that looks like this:

terraform {
  source = "git::git@github.com:foo/modules.git//frontend-app?ref=v0.0.3"

  extra_arguments "custom_vars" {
    commands = [
      "apply",
      "plan",
      "import",
      "push",
      "refresh"
    ]

    arguments = [
      "-var-file=../common.tfvars" # Note: This relative path will NOT work correctly!
    ]
  }
}

Note how the source parameter is set, so Terragrunt will download the frontend-app code from the modules repo into a temporary folder and run terraform in that temporary folder. Note also that there is an extra_arguments block that is trying to allow the frontend-app to read some shared variables from a common.tfvars file. Unfortunately, the relative path (../common.tfvars) won't work, as it will be relative to the temporary folder! Moreover, you can't use an absolute path, or the code won't work on any of your teammates' computers.

To make the relative path work, you need to use get_terragrunt_dir() to combine the path with the folder where the terragrunt.hcl file lives:

terraform {
  source = "git::git@github.com:foo/modules.git//frontend-app?ref=v0.0.3"

  extra_arguments "custom_vars" {
    commands = [
      "apply",
      "plan",
      "import",
      "push",
      "refresh"
    ]

    # With the get_terragrunt_dir() function, you can use relative paths!
    arguments = [
      "-var-file=${get_terragrunt_dir()}/../common.tfvars"
    ]
  }
}

For the example above, this path will resolve to /terraform-code/frontend-app/../common.tfvars, which is exactly what you want.

get_parent_terragrunt_dir

get_parent_terragrunt_dir() returns the absolute directory where the Terragrunt parent configuration file (by default terragrunt.hcl) lives. This is useful when you need to use relative paths with remote Terraform configurations and you want those paths relative to your parent Terragrunt configuration file and not relative to the temporary directory where Terragrunt downloads the code.

This function is very similar to get_terragrunt_dir() except it returns the root instead of the leaf of your terragrunt configuration folder.

/terraform-code
├── terragrunt.hcl
├── common.tfvars
├── app1
│   └── terragrunt.hcl
├── tests
│   ├── app2
│   |   └── terragrunt.hcl
│   └── app3
│       └── terragrunt.hcl

terraform {
  extra_arguments "common_vars" {
    commands = [
      "apply",
      "plan",
      "import",
      "push",
      "refresh"
    ]

    arguments = [
      "-var-file=${get_parent_terragrunt_dir()}/common.tfvars"
    ]
  }
}

The common.tfvars located in the terraform root folder will be included by all applications, whatever their relative location to the root.

get_terraform_commands_that_need_vars

get_terraform_commands_that_need_vars() returns the list of terraform commands that accept -var and -var-file parameters. This function is used when defining extra_arguments.

terraform {
  extra_arguments "common_var" {
    commands  = get_terraform_commands_that_need_vars()
    arguments = ["-var-file=${get_aws_account_id()}.tfvars"]
  }
}

get_terraform_commands_that_need_input

get_terraform_commands_that_need_input() returns the list of terraform commands that accept the -input=(true or false) parameter. This function is used when defining extra_arguments.

terraform {
  # Force Terraform to not ask for input value if some variables are undefined.
  extra_arguments "disable_input" {
    commands  = get_terraform_commands_that_need_input()
    arguments = ["-input=false"]
  }
}

get_terraform_commands_that_need_locking

get_terraform_commands_that_need_locking() returns the list of terraform commands that accept the -lock-timeout parameter. This function is used when defining extra_arguments.

terraform {
  # Force Terraform to keep trying to acquire a lock for up to 20 minutes if someone else already has the lock
  extra_arguments "retry_lock" {
    commands  = get_terraform_commands_that_need_locking()
    arguments = ["-lock-timeout=20m"]
  }
}

get_terraform_commands_that_need_parallelism

get_terraform_commands_that_need_parallelism() returns the list of terraform commands that accept the -parallelism parameter. This function is used when defining extra_arguments.

terraform {
  # Force Terraform to run with reduced parallelism
  extra_arguments "parallelism" {
    commands  = get_terraform_commands_that_need_parallelism()
    arguments = ["-parallelism=5"]
  }
}

get_aws_account_id

get_aws_account_id() returns the AWS account id associated with the current set of credentials. Example:

remote_state {
  backend = "s3"
  config = {
    bucket = "mycompany-${get_aws_account_id()}"
  }
}

This allows uniqueness of the storage bucket per AWS account (since bucket name must be globally unique).

It is also possible to configure variables specifically based on the account used:

terraform {
  extra_arguments "common_var" {
    commands = get_terraform_commands_that_need_vars()
    arguments = ["-var-file=${get_aws_account_id()}.tfvars"]
  }
}

run_cmd

run_cmd(command, arg1, arg2...) runs a shell command and returns the stdout as the result of the interpolation. The command is executed at the same folder as the terragrunt.hcl file. This is useful whenever you want to dynamically fill in arbitrary information in your Terragrunt configuration.

As an example, you could write a script that determines the bucket and DynamoDB table name based on the AWS account, instead of hardcoding the name of every account:

remote_state {
  backend = "s3"
  config = {
    bucket         = run_cmd("./get_names.sh", "bucket")
    dynamodb_table = run_cmd("./get_names.sh", "dynamodb")
  }
}

Before and After Hooks

Before Hooks or After Hooks are a feature of terragrunt that make it possible to define custom actions that will be called either before or after execution of the terraform command.

Here's an example:

terraform {
  before_hook "before_hook_1" {
    commands     = ["apply", "plan"]
    execute      = ["echo", "Foo"]
    run_on_error = true
  }

  before_hook "before_hook_2" {
    commands     = ["apply"]
    execute      = ["echo", "Bar"]
    run_on_error = false
  }

  before_hook "interpolation_hook_1" {
    commands     = ["apply", "plan"]
    execute      = ["echo", get_env("HOME", "HelloWorld")]
    run_on_error = false
  }

  after_hook "after_hook_1" {
    commands     = ["apply", "plan"]
    execute      = ["echo", "Baz"]
    run_on_error = true
  }

  after_hook "init_from_module" {
    commands = ["init-from-module"]
    execute  = ["cp", "${get_parent_terragrunt_dir()}/foo.tf", "."]
  }
}

Hooks support the following arguments:

• commands (required): the terraform commands that will trigger the execution of the hook.
• execute (required): the shell command to execute.
• run_on_error (optional): if set to true, this hook will run even if a previous hook hit an error, or in the case of "after" hooks, if the Terraform command hit an error. Default is false.
• init_from_module and init: This is not an argument, but a special name you can use for hooks that run during initialization. There are two stages of initialization: one is to download remote configurations using go-getter; the other is Auto-Init, which configures the backend and downloads provider plugins and modules. If you wish to execute a hook when Terragrunt is using go-getter to download remote configurations, name the hook init_from_module. If you wish to execute a hook when Terragrunt is using terraform init for Auto-Init, name the hook init.

Auto-Init

Auto-Init is a feature of Terragrunt that makes it so that terragrunt init does not need to be called explicitly before other terragrunt commands.

When Auto-Init is enabled (the default), terragrunt will automatically call terraform init during other commands (e.g. terragrunt plan) when terragrunt detects that:

• terraform init has never been called, or
• source needs to be downloaded, or
• the modules or remote state used by the module have changed since the previous call to terraform init.

As mentioned above, extra_arguments can be configured to allow customization of the terraform init command.

Note that there might be cases where terragrunt does not properly detect that terraform init needs be called. In this case, terraform would fail. Running terragrunt init again corrects this situation.

For some use cases, it might be desirable to disable Auto-Init. For example, if each user wants to specify a different -plugin-dir option to terraform init (and therefore it cannot be put in extra_arguments). To disable Auto-Init, use the --terragrunt-no-auto-init command line option or set the TERRAGRUNT_AUTO_INIT environment variable to false.

Disabling Auto-Init means that you must explicitly call terragrunt init prior to any other terragrunt commands for a particular configuration. If Auto-Init is disabled, and terragrunt detects that terraform init needs to be called, then terragrunt will fail.

Auto-Retry

Auto-Retry is a feature of terragrunt that will automatically address situations where a terraform command needs to be re-run.

Terraform can fail with transient errors which can be addressed by simply retrying the command again. In the event terragrunt finds one of these errors, the command will be re-run again automatically.

Example

$ terragrunt apply
...
Initializing provider plugins...
- Checking for available provider plugins on https://releases.hashicorp.com...
Error installing provider "template": error fetching checksums: Get https://releases.hashicorp.com/terraform-provider-template/1.0.0/terraform-provider-template_1.0.0_SHA256SUMS: net/http: TLS handshake timeout.

Terragrunt sees this error, and knows it is a transient error that can addressed by re-running the apply command.

auto-retry will try a maximum of three times to re-run the command, at which point it will deem the error as not transient, and accept the terraform failure. Retries will occur when the error is encountered, pausing for 5 seconds between retries.

Known errors that auto-retry will rerun, are maintained in the TerragruntOptions.RetryableErrors array. Future upgrades to terragrunt may include the ability to configure auto-retry by specifying additional error strings and configuring max retries and retry intervals the terragrunt config (PRs welcome!).

To disable auto-retry, use the --terragrunt-no-auto-retry command line option or set the TERRAGRUNT_AUTO_RETRY environment variable to false.

CLI Options

Terragrunt forwards all arguments and options to Terraform. The only exceptions are --version, terragrunt-info and arguments that start with the prefix --terragrunt-. The currently available options are:

• --terragrunt-config: A custom path to the terragrunt.hcl file. May also be specified via the TERRAGRUNT_CONFIG environment variable. The default path is terragrunt.hcl in the current directory (see Configuration for a slightly more nuanced explanation). This argument is not used with the apply-all, destroy-all, output-all, validate-all, and plan-all commands.

• --terragrunt-tfpath: A custom path to the Terraform binary. May also be specified via the TERRAGRUNT_TFPATH environment variable. The default is terraform in a directory on your PATH.

• --terragrunt-no-auto-init: Don't automatically run terraform init when other commands are run (e.g. terragrunt apply). Useful if you want to pass custom arguments to terraform init that are specific to a user or execution environment, and therefore cannot be specified as extra_arguments. For example, -plugin-dir. You must run terragrunt init yourself in this case if needed. terragrunt will fail if it detects that init is needed, but auto init is disabled. See Auto-Init

• --terragrunt-no-auto-retry: Don't automatically retry commands which fail with transient errors. See Auto-Retry

• --terragrunt-non-interactive: Don't show interactive user prompts. This will default the answer for all prompts to 'yes'. Useful if you need to run Terragrunt in an automated setting (e.g. from a script). May also be specified with the TF_INPUT environment variable.

• --terragrunt-working-dir: Set the directory where Terragrunt should execute the terraform command. Default is the current working directory. Note that for the apply-all, destroy-all, output-all, validate-all, and plan-all commands, this parameter has a different meaning: Terragrunt will apply or destroy all the Terraform modules in the subfolders of the terragrunt-working-dir, running terraform in the root of each module it finds.

• --terragrunt-download-dir: The path where to download Terraform code when using remote Terraform configurations. May also be specified via the TERRAGRUNT_DOWNLOAD environment variable. Default is .terragrunt-cache in the working directory. We recommend adding this folder to your .gitignore.

• --terragrunt-source: Download Terraform configurations from the specified source into a temporary folder, and run Terraform in that temporary folder. May also be specified via the TERRAGRUNT_SOURCE environment variable. The source should use the same syntax as the Terraform module source parameter. If you specify this argument for the apply-all, destroy-all, output-all, validate-all, or plan-all commands, Terragrunt will assume this is the local file path for all of your Terraform modules, and for each module processed by the xxx-all command, Terragrunt will automatically append the path of source parameter in each module to the --terragrunt-source parameter you passed in.

• --terragrunt-source-update: Delete the contents of the temporary folder before downloading Terraform source code into it. Can also be enabled by setting the TERRAGRUNT_SOURCE_UPDATE environment variable to true.

• --terragrunt-ignore-dependency-errors: *-all commands continue processing components even if a dependency fails

• --terragrunt-iam-role: Assume the specified IAM role ARN before running Terraform or AWS commands. May also be specified via the TERRAGRUNT_IAM_ROLE environment variable. This is a convenient way to use Terragrunt and Terraform with multiple AWS accounts.

• --terragrunt-exclude-dir: Unix-style glob of directories to exclude when running *-all commands. Modules under these directories will be excluded during execution of the commands. If a relative path is specified, it should be relative from --terragrunt-working-dir. Flag can be specified multiple times.

• --terragrunt-include-dir: Unix-style glob of directories to include when running *-all commands. Only modules under these directories (and all dependent modules) will be included during execution of the commands. If a relative path is specified, it should be relative from --terragrunt-working-dir. Flag can be specified multiple times.

• --terragrunt-ignore-external-dependencies: Dont attempt to include any external dependencies when running *-all commands

Configuration

Terragrunt configuration is defined in a terragrunt.hcl file. This uses the same HCL syntax as Terraform itself.

Here's an example:

include {
  path = find_in_parent_folders()
}

dependencies {
  paths = ["../vpc", "../mysql", "../redis"]
}

Terragrunt figures out the path to its config file according to the following rules:

1. The value of the --terragrunt-config command-line option, if specified.
2. The value of the TERRAGRUNT_CONFIG environment variable, if defined.
3. A terragrunt.hcl file in the current working directory, if it exists.
4. If none of these are found, exit with an error.

prevent_destroy

Terragrunt prevent_destroy boolean flag allows you to protect selected Terraform module. It will prevent destroy or destroy-all command to actually destroy resources of the protected module. This is useful for modules you want to carefully protect, such as a database, or a module that provides auth.

Example:

terraform {
  source = "git::git@github.com:foo/modules.git//app?ref=v0.0.3"
}

prevent_destroy = true

skip

The terragrunt skip boolean flag can be used to protect modules you don't want any changes to or just to skip modules that don't define any infrastructure by themselves. When set to true, all terragrunt commands will skip the selected module.

Consider the following file structure:

root
├── terragrunt.hcl
├── prod
│   └── terragrunt.hcl
├── dev
│   └── terragrunt.hcl
└── qa
    └── terragrunt.hcl

In some cases, the root level terragrunt.hcl file is solely used to DRY up your Terraform configuration by being included in the other terragrunt.hcl files. In this case, you do not want the xxx-all commands to process the root level terragrunt.hcl since it does not define any infrastructure by itself. To make the xxx-all commands skip the root level terragrunt.hcl file, you can set skip = true:

skip = true

The skip flag must be set explicitly in terragrunt modules that should be skipped. If you set skip = true in a terragrunt.hcl file that is included by another terragrunt.hcl file, only the terragrunt.hcl file that explicitly set skip = true will be skipped.

Clearing the Terragrunt cache

Terragrunt creates a .terragrunt-cache folder in the current working directory as its scratch directory. It downloads your remote Terraform configurations into this folder, runs your Terraform commands in this folder, and any modules and providers those commands download also get stored in this folder. You can safely delete this folder any time and Terragrunt will recreate it as necessary.

If you need to clean up a lot of these folders (e.g., after terragrunt apply-all), you can use the following commands on Mac and Linux:

Recursively find all the .terragrunt-cache folders that are children of the current folder:

find . -type d -name ".terragrunt-cache"

If you are ABSOLUTELY SURE you want to delete all the folders that come up in the previous command, you can recursively delete all of them as follows:

find . -type d -name ".terragrunt-cache" -prune -exec rm -rf {} \;

Also consider setting the TERRAGRUNT_DOWNLOAD environment variable if you wish to place the cache directories somewhere else.

Contributing

Terragrunt is an open source project, and contributions from the community are very welcome! Please check out the Contribution Guidelines and Developing Terragrunt for instructions.

Developing Terragrunt

Running locally

To run Terragrunt locally, use the go run command:

go run main.go plan

Dependencies

• Terragrunt uses dep, a vendor package management tool for golang. See the dep repo for installation instructions.

Running tests

Note: The tests in the dynamodb folder for Terragrunt run against a real AWS account and will add and remove real data from DynamoDB. DO NOT hit CTRL+C while the tests are running, as this will prevent them from cleaning up temporary tables and data in DynamoDB. We are not responsible for any charges you may incur.

Before running the tests, you must configure your AWS credentials and AWS IAM policies.

To run all the tests:

go test -v ./...

To run only the tests in a specific package, such as the package remote:

cd remote
go test -v

And to run a specific test, such as TestToTerraformRemoteConfigArgsNoBackendConfigs in package remote:

cd remote
go test -v -run TestToTerraformRemoteConfigArgsNoBackendConfigs

Debug logging

If you set the TERRAGRUNT_DEBUG environment variable to "true", the stack trace for any error will be printed to stdout when you run the app.

Error handling

In this project, we try to ensure that:

1. Every error has a stacktrace. This makes debugging easier.
2. Every error generated by our own code (as opposed to errors from Go built-in functions or errors from 3rd party libraries) has a custom type. This makes error handling more precise, as we can decide to handle different types of errors differently.

To accomplish these two goals, we have created an errors package that has several helper methods, such as errors.WithStackTrace(err error), which wraps the given error in an Error object that contains a stacktrace. Under the hood, the errors package is using the go-errors library, but this may change in the future, so the rest of the code should not depend on go-errors directly.

Here is how the errors package should be used:

1. Any time you want to create your own error, create a custom type for it, and when instantiating that type, wrap it with a call to errors.WithStackTrace. That way, any time you call a method defined in the Terragrunt code, you know the error it returns already has a stacktrace and you don't have to wrap it yourself.
2. Any time you get back an error object from a function built into Go or a 3rd party library, immediately wrap it with errors.WithStackTrace. This gives us a stacktrace as close to the source as possible.
3. If you need to get back the underlying error, you can use the errors.IsError and errors.Unwrap functions.

Formatting

Every source file in this project should be formatted with go fmt. There are few helper scripts and targets in the Makefile that can help with this (mostly taken from the terraform repo):

1. make fmtcheck

   Checks to see if all source files are formatted. Exits 1 if there are unformatted files.

2. make fmt

   Formats all source files with gofmt.

3. make install-pre-commit-hook

   Installs a git pre-commit hook that will run all of the source files through gofmt.

To ensure that your changes get properly formatted, please install the git pre-commit hook with make install-pre-commit-hook.

Releasing new versions

To release a new version, just go to the Releases Page and create a new release. The CircleCI job for this repo has been configured to:

1. Automatically detect new tags.
2. Build binaries for every OS using that tag as a version number.
3. Upload the binaries to the release in GitHub.

See .circleci/config.yml for details.

License

This code is released under the MIT License. See LICENSE.txt.