2021-05-02-terragrunt-advantages

Terraform weaknesses that can be helped with Terragrunt:

• the lack of Terraform module dependencies:

  it is not possible to dependency chain two modules in Terraform because it’s simply not supported. Terragrunt solves this by implementing the dependencies statement that allows other modules to be executed first.

• no retries on known errors: some Terraform errors will go away just by rerunning the apply command

• no possibility to deploy the same version of a Terraform module across all our environments: let’s say we want to make a change to our VPC Terraform module. Ideally, that change should be deployed as an artifact, tagged with a proper version and distributed to all environments. Terragrunt solves this by sourcing a particular branch/tag for its deployment.

• no possibility of keeping the Terraform backend configuration DRY across all our environments (S3 state bucket, region, DynamoDB table etc): for every sub-component (EKS, S3, IAM, MSK etc) of our infrastructure we had to redefine the Terraform backend configuration over and over again. More sub-components, and more pain for our SRE team. Terragrunt solves this issue by using the path_relative_to_include() function to figure out the current directory.

• when the Terraform code grows significantly enough, it must be organised into folders: Terraform has no way of running a global plan or apply command across all those folders. Terragrunt has a plan-all and apply-all to make it easier to run the Terraform code across all folders.