Awesome

Update values in terraform.tfvars using annotations

This project has become redundant (yay!)

The same functionality is available natively in Terragrunt since version 0.19.20 (released 15th of August 2019).

See PR #3 for the explanation and some extra unreleased code if you want to continue developing this for Terraform.

As of today, Terraform 0.11 and 0.12 support only static (known, fixed, already computed) values in tfvars files. There is no way to use Terraform interpolation functions, or data-sources inside tfvars files in Terraform to update values.

While working on modules.tf (a tool which converts visual diagrams created with Cloudcraft.co into Terraform configurations), I had a need to generate code which would chain invocations of Terraform AWS modules and pass arguments between them without requiring any extra Terraform code as a glue. Terragrunt is a great fit for this, it allows to reduce amount of Terraform configurations by reusing Terraform modules and providing arguments as values in tfvars files.

Some languages I know have concepts like annotations and decorators, so at first I made a shell script which replaced values in tfvars based on annotations and was called by Terragrunt hooks. tfvars-annotations shares the same goal and it has no external dependencies (except terraform or terragrunt).

Use cases

modules.tf and Terragrunt (recommended)
Terraform (not implemented yet)
General example - AMI ID, AWS region

Features

Supported annotations:

terragrunt_output:
- @tfvars:terragrunt_output.vpc.vpc_id
- @tfvars:terragrunt_output.security-group.this_security_group_id
terraform_output
data-sources generic

Type wrapping:

to_list: Wrap original value with [] to make it it as a list

How to use

Run tfvars-annotations before terraform plan, apply, refresh.

It will process tfvars file in the current directory and set updated values.

E.g.:

$ tfvars-annotations examples/project1-terragrunt/eu-west-1/app
$ terraform plan

How to disable processing entirely

Put @tfvars:disable_annotations anywhere in the terraform.tfvars to not process the file.

Examples

See examples for some basics.

To-do

Get values from other sources:

data sources generic
aws_account_id or aws_region data sources

terragrunt_outputs from stacks:

in any folder
in current region

cache values unless stack is changed/updated
functions (limit(2), to_list)
rewrite in go (invoke like this => update_dynamic_values_in_tfvars ${get_parent_tfvars_dir()}/${path_relative_to_include()})
make it much faster, less verbose
add dry-run flag
Proposed syntax:

@tfvars:terragrunt_output.security-group_5.this_security_group_id.to_list
@tfvars:terragrunt_output.["eu-west-1/security-group_5"].this_security_group_id.to_list
@tfvars:terragrunt_output.["global/route53-zones"].zone_id
@tfvars:terragrunt_data.aws_region.zone_id
@tfvars:terragrunt_data.aws_region[{current=true}].zone_id

Bugs

Add support for maps (and lists of maps). Strange bugs with rendering comments in wrong places.

Installation

On OSX, install it with Homebrew (not enough github stars to get it to the official repo):

brew install -s HomebrewFormula/tfvars-annotations.rb

Alternatively, you can download a release suitable for your platform and unzip it. Make sure the tfvars-annotations binary is executable, and you're ready to go.

You can also install it like this:

go get github.com/antonbabenko/tfvars-annotations

Or run it from source:

go run . -debug examples/project1-terragrunt/eu-west-1/app
go run . examples/project1-terragrunt/eu-west-1/app

Release

Make GitHub Release: hub release create v0.0.3. Then Github Actions will build binaries and attach them to Github release.
Update Homebrew version in HomebrewFormula/tfvars-annotations.rb. Install locally - brew install -s HomebrewFormula/tfvars-annotations.rb

Authors

This project is created and maintained by Anton Babenko with the help from different contributors.

License

This work is licensed under MIT License. See LICENSE for full details.