Terragrunt
Terragrunt is a thin wrapper for Terraform that provides extra tools for working with multiple Terraform modules, remote state, and locking.
Quick start
-
Install Terraform.
-
Install Terragrunt by going to the Releases Page, downloading the binary for your OS, renaming it to
terragrunt
, and adding it to your PATH. -
Go into a folder with your Terraform configurations (
.tf
files) and create aterraform.tfvars
file with aterragrunt = { ... }
block that contains the configuration for Terragrunt (check out the Use cases section for the types of configuration Terragrunt supports):terragrunt = { # (put your Terragrunt configuration here) }
-
Now, instead of running
terraform
directly, run all the standard Terraform commands usingterragrunt
: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
terraform.tfvars
file, Terragrunt can configure remote state, locking, extra arguments, and lots more.
Use cases
Terragrunt supports the following use cases:
- Keep your Terraform code DRY
- Keep your remote state configuration DRY
- Keep your CLI flags DRY
- Work with multiple Terraform modules
Keep your Terraform code DRY
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 .tfvars
file per component (e.g. app/terraform.tfvars
, mysql/terraform.tfvars
, etc). This gives you
the following file layout:
└── live
├── prod
│ ├── app
│ │ └── terraform.tfvars
│ ├── mysql
│ │ └── terraform.tfvars
│ └── vpc
│ └── terraform.tfvars
├── qa
│ ├── app
│ │ └── terraform.tfvars
│ ├── mysql
│ │ └── terraform.tfvars
│ └── vpc
│ └── terraform.tfvars
└── stage
├── app
│ └── terraform.tfvars
├── mysql
│ └── terraform.tfvars
└── vpc
└── terraform.tfvars
Notice how there are no Terraform configurations (.tf
files) in any of the folders. Instead, each .tfvars
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/terraform.tfvars
may look like this:
terragrunt = {
terraform {
source = "git::git@github.com:foo/modules.git//app?ref=v0.0.3"
}
}
instance_count = 3
instance_type = "t2.micro"
(Note: the double slash (//
) is intentional and required. It's part of Terraform's Git syntax for module
sources.)
And prod/app/terraform.tfvars
may look like this:
terragrunt = {
terraform {
source = "git::git@github.com:foo/modules.git//app?ref=v0.0.1"
}
}
instance_count = 10
instance_type = "m2.large"
Notice how the two terraform.tfvars
files set the source
URL to the same app
module, but at different
versions (i.e. stage
is testing out a newer version of the module). They also set the parameters for the
app
module to different values that are appropriate for the environment: smaller/fewer servers in stage
to save money, larger/more instances in prod
for scalability and high availability.
How to use remote configurations
Once you've set up your live
and modules
repositories, all you need to do is run terragrunt
commands in the
live
repository. For example, to deploy the app
module in qa, you would do the following:
cd live/qa/app
terragrunt apply
When Terragrunt finds the terraform
block with a source
parameter in live/qa/app/terraform.tfvars
file, it will:
-
Download the configurations specified via the
source
parameter into a temporary folder. This downloading is done by using the terraform init command, so thesource
parameter supports the exact same syntax as the module source parameter, including local file paths, Git URLs, and Git URLs withref
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. -
Copy all files from the current working directory into the temporary folder. This way, Terraform will automatically read in the variables defined in the
terraform.tfvars
file. -
Execute whatever Terraform command you specified in that temporary folder.
DRY Terraform code and immutable infrastructure
With this new approach, copy/paste between environments is minimized. The .tfvars
files contain solely the variables
that are different between environments. To create a new environment, you copy an old one and update just the
environment-specific values in the .tfvars
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/terraform.tfvars
and
prod/app/terraform.tfvars
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.)
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 /tmp/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 (
terraform.tfvars
), such as in anextra_arguments
block, you can't use hard-coded absolute file paths, or it won't work on your teammates' computers. Therefore, you should use a relative file path with theget_tfvars_dir()
helper:terragrunt = { 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_tfvars_dir helper, you can use relative paths! arguments = [ "-var-file=${get_tfvars_dir()}/../common.tfvars", "-var-file=terraform.tfvars" ] } } }
See the get_tfvars_dir() documentation for more details.
Keep your remote state configuration DRY
Motivation
Terraform supports remote state storage via a variety of backends that you configure as follows:
terraform {
backend "s3" {
bucket = "my-terraform-state"
key = "frontend-app/terraform.tfstate"
region = "us-east-1"
encrypt = true
lock_table = "my-lock-table"
}
}
Unfortunately, the backend
configuration does not support interpolation. 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:
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 terraform.tfvars
file in the root folder and in each of the
Terraform modules:
├── terraform.tfvars
├── backend-app
│ ├── main.tf
│ └── terraform.tfvars
├── frontend-app
│ ├── main.tf
│ └── terraform.tfvars
├── mysql
│ ├── main.tf
│ └── terraform.tfvars
└── vpc
├── main.tf
└── terraform.tfvars
In your root terraform.tfvars
file, you can define your entire remote state configuration just once in a
remote_state
block, as follows:
terragrunt = {
remote_state {
backend = "s3"
config {
bucket = "my-terraform-state"
key = "${path_relative_to_include()}/terraform.tfstate"
region = "us-east-1"
encrypt = true
lock_table = "my-lock-table"
}
}
}
The remote_state
block supports all the same backend types
as Terraform. 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.
In each of the child terraform.tfvars
files, such as mysql/terraform.tfvars
, you can tell Terragrunt to
automatically include all the settings from the root terraform.tfvars
file as follows:
terragrunt = {
include {
path = "${find_in_parent_folders()}"
}
}
The include
block tells Terragrunt to use the exact settings from the terraform.tfvars
file specified via the
path
parameter. It behaves exactly as if you had copy/pasted the contents of the root terraform.tfvars
file into
mysql/terraform.tfvars
, but this approach is much easier to maintain! Note that if you include any other settings
in the terragrunt
block of a child .tfvars
file, it will override the settings in the parent.
The terraform.tfvars
files above use two helper functions:
-
find_in_parent_folders()
: This helper returns the path to the firstterraform.tfvars
file it finds in the parent folders above the currentterraform.tfvars
file. In the example above, the call tofind_in_parent_folders()
inmysql/terraform.tfvars
will return../terraform.tfvars
. This way, you don't have to hard code thepath
parameter in every module. -
path_relative_to_include()
: This helper function returns the relative path between the currentterraform.tfvars
file and the path specified in itsinclude
block. We typically use this in a rootterraform.tfvars
file so that each Terraform child module stores its Terraform state at a differentkey
. For example, themysql
module will have itskey
parameter resolve tomysql/terraform.tfstate
and thefrontend-app
module will have itskey
parameter resolve tofrontend-app/terraform.tfstate
.
See the helper functions docs for more info.
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 inremote_state.config
doesn't already exist, Terragrunt will create it automatically, with versioning enabled. -
DynamoDB table: If you are using the S3 backend for remote state storage and you specify a
lock_table
(a DynamoDB table used for locking) inremote_state.config
, if that table doesn't already exist, Terragrunt will create it automatically, including a primary key calledLockID
.
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.
Keep your CLI flags DRY
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 terraform.tfvars
file:
terragrunt = {
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"
]
}
}
}
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 add, a list of arguments
or required_var_files
or optional_var_files
to add.
With the configuration above, when you run terragrunt apply
, Terragrunt will call Terraform as follows:
> terragrunt apply
terraform apply -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 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:
terragrunt = {
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"
]
}
# 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
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, terraform will complain. Using
optional_var_files
instead, terragrunt will only add the -var-file=<your file>
for existing files. This allows many conditional
configurations based on environment variables as you can see in the following example:
/my/tf
├── terraform.tfvars
├── prod.tfvars
├── us-west-2.tfvars
├── backend-app
│ ├── main.tf
│ ├── dev.tfvars
│ └── terraform.tfvars
├── frontend-app
│ ├── main.tf
│ ├── us-east-1.tfvars
│ └── terraform.tfvars
terragrunt = {
terraform {
extra_arguments "conditional_vars" {
commands = [
"apply",
"plan",
"import",
"push",
"refresh"
]
required_var_files = [
"${get_parent_tfvars_dir()}/terraform.tfvars"
]
optional_var_files = [
"${get_parent_tfvars_dir()}/${get_env("TF_VAR_env", "dev")}.tfvars",
"${get_parent_tfvars_dir()}/${get_env("TF_VAR_region", "us-east-1")}.tfvars"
"${get_tfvars_dir()}/${get_env("TF_VAR_env", "dev")}.tfvars",
"${get_tfvars_dir()}/${get_env("TF_VAR_region", "us-east-1")}.tfvars"
]
}
}
See the get_tfvars_dir() and get_parent_tfvars_dir() documentation for more details.
Note that terragrunt cannot interpolate terraform variables (${var.xxx}) in the terragrunt configuration, your variables have to be defined through TF_VAR_xxx environment variable to be referred by terragrunt.
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:
terragrunt = {
terraform {
extra_arguments "bucket" {
arguments = [
"-var", "bucket=example.bucket.name",
]
commands = [
"apply",
"plan",
"import",
"push",
"refresh"
]
}
}
}
With the configuration above, when you run terragrunt apply
, Terragrunt will call Terraform as follows:
> terragrunt apply
terraform apply -var bucket=example.bucket.name
Work with multiple Terraform modules
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 terraform.tfvars
file to each module:
root
├── backend-app
│ ├── main.tf
│ └── terraform.tfvars
├── frontend-app
│ ├── main.tf
│ └── terraform.tfvars
├── mysql
│ ├── main.tf
│ └── terraform.tfvars
├── redis
│ ├── main.tf
│ └── terraform.tfvars
└── vpc
├── main.tf
└── terraform.tfvars
Inside each terraform.tfvars
file, add a terragrunt = { ... }
block to identify this as a module managed by
Terragrunt (the block can be empty or include any of the configs described in this documentation):
terragrunt = {
# Put your Terragrunt configuration here
}
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 terraform.tfvars
files with a terragrunt = { ... }
block, and run terragrunt apply
in each
one 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
│ └── terraform.tfvars
├── frontend-app
│ ├── main.tf
│ └── terraform.tfvars
├── mysql
│ ├── main.tf
│ └── terraform.tfvars
├── redis
│ ├── main.tf
│ └── terraform.tfvars
└── vpc
├── main.tf
└── terraform.tfvars
Let's assume you have the following dependencies between Terraform modules:
backend-app
depends onmysql
,redis
, andvpc
frontend-app
depends onbackend-app
andvpc
mysql
depends onvpc
redis
depends onvpc
vpc
has no dependencies
You can express these dependencies in your terraform.tfvars
config files using a dependencies
block. For example,
in backend-app/terraform.tfvars
you would specify:
terragrunt = {
dependencies {
paths = ["../vpc", "../mysql", "../redis"]
}
}
Similarly, in frontend-app/terraform.tfvars
, you would specify:
terragrunt = {
dependencies {
paths = ["../vpc", "../backend-app"]
}
}
Once you've specified the dependencies in each terraform.tfvars
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:
- Deploy the VPC
- Deploy MySQL and Redis in parallel
- Deploy the backend-app
- 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.
Terragrunt details
This section contains detailed documentation for the following aspects of Terragrunt:
- Helper functions
- CLI options
- Migrating from Terragrunt v0.11.x and Terraform 0.8.x and older
- Terragrunt config files
- Developing Terragrunt
- License
Helper functions
Terragrunt allows you to use the same interpolation syntax as Terraform (${...}
) to call helper functions. Note
that helper functions only work within a terragrunt = { ... }
block. Terraform does NOT process interpolations in
.tfvars
files.
Here are the supported helper functions:
- find_in_parent_folders
- path_relative_to_include
- path_relative_from_include
- get_env
- get_tfvars_dir
- get_parent_tfvars_dir
- get_aws_account_id
find_in_parent_folders
find_in_parent_folders()
searches up the directory tree from the current .tfvars
file and returns the relative path
to to the first terraform.tfvars
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 .tfvars
file:
terragrunt = {
include {
path = "${find_in_parent_folders()}"
}
}
path_relative_to_include
path_relative_to_include()
returns the relative path between the current .tfvars
file and the path
specified in
its include
block. For example, consider the following folder structure:
├── terraform.tfvars
└── prod
└── mysql
└── terraform.tfvars
└── stage
└── mysql
└── terraform.tfvars
Imagine prod/mysql/terraform.tfvars
and stage/mysql/terraform.tfvars
include all settings from the root
terraform.tfvars
file:
terragrunt = {
include {
path = "${find_in_parent_folders()}"
}
}
The root terraform.tfvars
can use the path_relative_to_include()
in its remote_state
configuration to ensure
each child stores its remote state at a different key
:
terragrunt = {
remote_state {
backend = "s3"
config {
bucket = "my-terraform-bucket"
region = "us-east-1"
key = "${path_relative_to_include()}/terraform.tfstate"
}
}
}
The resulting key
will be prod/mysql/terraform.tfstate
for the prod mysql
module and
stage/mysql/terraform.tfstate
for the stage mysql
module.
path_relative_from_include
path_relative_from_include()
returns the relative path between the path
specified in its include
block and the current
.tfvars
file (it is the counterpart of path_relative_to_include()
). For example, consider the following folder structure:
├── sources
| ├── mysql
| | └── *.tf
| └── secrets
| └── mysql
| └── *.tf
└── terragrunt
└── common.tfvars
├── mysql
| └── terraform.tfvars
├── secrets
| └── mysql
| └── terraform.tfvars
└── terraform.tfvars
Imagine terragrunt/mysql/terraform.tfvars
and terragrunt/secrets/mysql/terraform.tfvars
include all settings from the root
terraform.tfvars
file:
terragrunt = {
include {
path = "${find_in_parent_folders()}"
}
}
The root terraform.tfvars
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:
terragrunt = {
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:
terragrunt = {
terraform = {
...
extra_arguments "common_var" {
commands = [
"apply",
"plan",
"import",
"push",
"refresh"
]
arguments = [
"-var-file=${get_tfvars_dir()}/${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:
terragrunt = {
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 the 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
helper function.
get_tfvars_dir
get_tfvars_dir()
returns the directory where the Terragrunt configuration file (by default, terraform.tfvars
) 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
│ └── terraform.tfvars
Inside of /terraform-code/frontend-app/terraform.tfvars
you might try to write code that looks like this:
terragrunt = {
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!
"-var-file=terraform.tfvars"
]
}
}
}
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 the get_tfvars_dir()
helper to combine the path with the folder where
the .tfvars
file lives:
terragrunt = {
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_tfvars_dir helper, you can use relative paths!
arguments = [
"-var-file=${get_tfvars_dir()}/../common.tfvars",
"-var-file=terraform.tfvars"
]
}
}
}
For the example above, this path will resolve to /terraform-code/frontend-app/../common.tfvars
, which is exactly
what you want.
get_parent_tfvars_dir
get_parent_tfvars_dir()
returns the absolute directory where the Terragrunt parent configuration file (by default, terraform.tfvars
) 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_tfvars_dir() except it returns the root instead of the leaf of your terragrunt configuration folder.
/terraform-code
├── terraform.tfvars
├── common.tfvars
├── app1
│ └── terraform.tfvars
├── tests
│ ├── app2
│ | └── terraform.tfvars
│ └── app3
│ └── terraform.tfvars
terragrunt = {
terraform {
extra_arguments "common_vars" {
commands = [
"apply",
"plan",
"import",
"push",
"refresh"
]
arguments = [
"-var-file=${get_parent_tfvars_dir()}/common.tfvars"
]
}
}
}
The common.tfvars located in the terraform root folder will be included by all applications, whatever their relative location to the root.
get_aws_account_id
get_aws_account_id()
returns the AWS account id associated with the current set of credentials. Example:
terragrunt = {
remote_state {
backend = "s3"
config {
bucket = "mycompany-${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:
terragrunt = {
terraform = {
...
extra_arguments "common_var" {
commands = [
"apply",
"plan",
"import",
"push",
"refresh"
]
arguments = [
"-var-file=${get_aws_account_id()}.tfvars",
]
}
}
}
CLI Options
Terragrunt forwards all arguments and options to Terraform. The only exceptions are --version
and arguments that
start with the prefix --terragrunt-
. The currently available options are:
-
--terragrunt-config
: A custom path to theterraform.tfvars
file. May also be specified via theTERRAGRUNT_CONFIG
environment variable. The default path isterraform.tfvars
in the current directory (see Terragrunt config files for a slightly more nuanced explanation). This argument is not used with theapply-all
,destroy-all
,output-all
andplan-all
commands. -
--terragrunt-tfpath
: A custom path to the Terraform binary. May also be specified via theTERRAGRUNT_TFPATH
environment variable. The default isterraform
in a directory on your PATH. -
--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). -
--terragrunt-working-dir
: Set the directory where Terragrunt should execute theterraform
command. Default is the current working directory. Note that for theapply-all
anddestroy-all
directories, this parameter has a different meaning: Terragrunt will apply or destroy all the Terraform modules in the subfolders of theterragrunt-working-dir
, runningterraform
in the root of each module it finds. -
--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 theTERRAGRUNT_SOURCE
environment variable. The source should use the same syntax as the Terraform module source parameter. This argument is not used with theapply-all
,destroy-all
,output-all
andplan-all
commands. -
--terragrunt-source-update
: Delete the contents of the temporary folder before downloading Terraform source code into it. -
--terragrunt-ignore-dependency-errors
:*-all
commands continue processing components even if a dependency fails
Terragrunt config files
The current version of Terragrunt expects configuration to be defined in a terraform.tfvars
file. Previous
versions defined the config in a .terragrunt
file. The .terragrunt
format is now deprecated!
For backwards compatibility, Terragrunt will continue to support the .terragrunt
file format for a short period of
time. Check out the next section for how this works. Note that you will get a warning in your logs every time you run
Terragrunt with a .terragrunt
file, and we will eventually stop supporting this older format, so we recommend
migrating to the terraform.tfvars
format ASAP!
Config file search paths
Terragrunt figures out the path to its config file according to the following rules:
- The value of the
--terragrunt-config
command-line option, if specified. - The value of the
TERRAGRUNT_CONFIG
environment variable, if defined. - A
.terragrunt
file in the current working directory, if it exists. - A
terraform.tfvars
file in the current working directory, if it exists. - If none of these are found, exit with an error.
The --terragrunt-config
parameter is only used by Terragrunt and has no effect on which variable files are loaded by Terraform. Terraform will automatically read variables from a file named terraform.tfvars, but if you want it to read variables from some other .tfvars file, you must pass it in using the --var-file
argument:
terragrunt plan --terragrunt-config example.tfvars --var-file example.tfvars
Migrating from .terragrunt to terraform.tfvars
The configuration in a .terragrunt
file is identical to that of the terraform.tfvars
file, except the
terraform.tfvars
file requires you to wrap that configuration in a terragrunt = { ... }
block.
For example, if this is your .terragrunt
file:
include {
path = "${find_in_parent_folders()}"
}
dependencies {
paths = ["../vpc", "../mysql", "../redis"]
}
The equivalent terraform.tfvars
file is:
terragrunt = {
include {
path = "${find_in_parent_folders()}"
}
dependencies {
paths = ["../vpc", "../mysql", "../redis"]
}
}
To migrate, all you need to do is:
- Copy all the contents of the
.terragrunt
file. - Paste those contents into a
terragrunt = { ... }
block in aterraform.tfvars
file. - Delete the
.terragrunt
file.
Migrating from Terragrunt v0.11.x and Terraform 0.8.x and older
Background
Terragrunt was originally created to support two features that were not available in Terraform: defining remote state configuration in a file (rather than via CLI commands) and locking. As of version 0.9.0, Terraform now supports both of these features natively, so we have had to make changes to Terragrunt:
- Terragrunt still supports remote state configuration so you can take advantage of Terragrunt's interpolation functions.
- Terragrunt no longer supports locking.
Migration instructions
If you were using Terragrunt <= v0.11.x and Terraform <= 0.8.x, here is how to migrate:
-
In your Terraform code (the
.tf
files), you must now define abackend
. For example, to use S3 as a remote state backend, you will need to add the following to your Terraform code:# main.tf terraform { # The configuration for this backend will be filled in by Terragrunt backend "s3" {} }
Note that you can leave the configuration of the
backend
empty and allow Terragrunt to provide that configuration instead. This allows you to keep your remote state configuration more DRY by taking advantage of Terragrunt's interpolation functions:# terraform.tfvars terragrunt = { remote_state { backend = "s3" config { bucket = "my-terraform-state" key = "${path_relative_to_include()}/terraform.tfstate" region = "us-east-1" encrypt = true } } }
-
Remove any
lock { ... }
blocks from your Terragrunt configurations, as these are no longer supported.If you were storing remote state in S3 and relying on DynamoDB as a locking mechanism, Terraform now supports that natively. To enable it, simply add the
lock_table
parameter to your S3 backend configuration. If you configure your S3 backend using Terragrunt, then Terragrunt will automatically create thelock_table
for you if that table doesn't already exist:# terraform.tfvars terragrunt = { remote_state { backend = "s3" config { bucket = "my-terraform-state" key = "${path_relative_to_include()}/terraform.tfstate" region = "us-east-1" encrypt = true # Tell Terraform to do locking using DynamoDB. Terragrunt will automatically create this table for you if # it doesn't already exist. lock_table = "my-lock-table" } } }
NOTE: We recommend using a completely new lock table name and NOT reusing the lock table from older versions of Terragrunt, as that older table had a different structure than what Terraform expects, and Terragrunt will not automatically recreate it.
If you would like Terraform to automatically retry locks like Terragrunt did (this is particularly useful when running Terraform as part of an automated script, such as a CI build), you use an
extra_arguments
block:# terraform.tfvars terragrunt = { remote_state { backend = "s3" config { bucket = "my-terraform-state" key = "${path_relative_to_include()}/terraform.tfstate" region = "us-east-1" encrypt = true # Tell Terraform to do locking using DynamoDB. Terragrunt will automatically create this table for you if # it doesn't already exist. lock_table = "my-lock-table" } } 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" ] } } }
Developing terragrunt
Running locally
To run Terragrunt locally, use the go run
command:
go run main.go plan
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 as explained in the DynamoDB locking prerequisites section.
To run all the tests:
go test -v -parallel 128 $(glide novendor)
To run only the tests in a specific package, such as the package remote
:
cd remote
go test -v -parallel 128
And to run a specific test, such as TestToTerraformRemoteConfigArgsNoBackendConfigs
in package remote
:
cd remote
go test -v -parallel 128 -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:
- Every error has a stacktrace. This makes debugging easier.
- 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:
- 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. - 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. - If you need to get back the underlying error, you can use the
errors.IsError
anderrors.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):
-
make fmtcheck
Checks to see if all source files are formatted. Exits 1 if there are unformatted files.
-
make fmt
Formats all source files with
gofmt
. -
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:
- Automatically detect new tags.
- Build binaries for every OS using that tag as a version number.
- Upload the binaries to the release in GitHub.
See circle.yml
and _ci/build-and-push-release-asset.sh
for details.
License
This code is released under the MIT License. See LICENSE.txt.