Interpolate variables in terraform backend config

[roderickrandolph]

Terraform Version

Terraform v0.9.0-beta1

Affected Resource(s)

core

Terraform Configuration Files

provider "aws" { region = "us-east-1" }

terraform {
  backend "s3" {
    bucket = "my-bucket-${var.aws_region}"
    key = "${var.stack_name}.tfstate"
    region = "${var.aws_region}"
    encrypt = "1"
  }
}
variable "aws_region" { default = "us-east-1" }
variable "stack_name" { default = "my-stack" }

Debug Output

N/A

Panic Output

N/A

Expected Behavior

Terraform will interpolate all variables provided in the backend configuration (i.e. ${var.aws_region} and ${var.stack_name})

Actual Behavior

Terraform treats ${var.stack_name} and ${var.aws_region} as literal strings causing a terraform plan/apply to fail.

Error loading state: InvalidEndpointURL: invalid endpoint uri
caused by: parse https://s3.${var.aws_region}.amazonaws.com/{Bucket}/{Key+}: invalid character "{" in host name

Steps to Reproduce

Please list the steps required to reproduce the issue, for example:

1. terraform init
2. terraform plan

[mitchellh]

This isn't allowed and beta 2 will properly give you an error message. Rather than re-explain, I'll link you to the PR with the discussion we had! #12067 We do want you to be able to parameterize backends but for now that'll be restricted to partial configs with -backend-config on init.

[roderickrandolph]

Thank you. I didn't realize there was a previous discussion on this topic. I actually looked before opening this issue too.

General feedback:
From a UX perspective the previous behavior of passing in multiple -backend-config as K/V pairs on the command line was preferred over the new behavior of generating a separate throw away config file for each environment stack. Overall, I like the new terraform init direction but the partial backend config file seems like a step backwards from a UX perspective.

Also, given the argument name I initially assumed -backend-config for terraform init would behave like it did for terraform remote config and accept K/V pairs. After reading the docs more closely I realized it takes a file path instead. Others will probably have similar experiences too as they make the transition to 0.9. Perhaps a different argument name could reduce the confusion. Just a thought.

[mitchellh]

@roderickrandolph That's a good point. The reason we did away with K/V was that it left data in your CLI history, but I can see how it is much easier than the file-based approach. Let me think about it a bit. Thanks!

[sarmadali20]

@roderickrandolph what's the better UX alternative for this? I ran into this problem trying to store state files of k8s cluster in Artifactory so that Jenkins pipeline can create clusters on demand.

[ghost]

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