How to use terraform to ignore previous execution(state) [duplicate] - amazon-s3

Question

I'm a bit of a newbie with Terraform and still working my way through the documentation, have not yet been able to find a way to accomodate the set up I need to achieve for a specific solution and hoping that some kind soul may be able to give me a push in the right direction.
I'm trying to manage a single set of paramaterised templates which deploy everything needed to support a new application we are working on in GCP. What I am trying to achieve is being able to deploy those templates to three different environments, each environment being in a distinct GCP project, by itself.
The plan is, as per recommendations, run terraform and pass in
a) The specific .tfvars file depending on the environment/project being deployed to (dev/test/prod).
b) Use the -chdir parameter to tell Terraform to pick up all the templates from 'infra-common' folder.
The tricky part is that we want each environment (gcp project) to host it's own state file in gcs/storage.
I had been looking at workspaces but it appears that workspaces will just create state subfolders on a single backend.
Question: Can this be done or is there a better way to do it?
Thanks!

Answer 1

You can use --backend-config for this. Here's how you can achieve the desired behavior:
Create a .config file for each environment (dev.config, test.config, prod.config) which contain the name of the gcs bucket (which must already exist) for the respective environment
Specify the common backend in a single remote_state.tf file
Here's how it would look:
config/dev.config:
bucket = "tf-state-dev"
config/test.config:
bucket = "tf-state-test"
config/prod.config:
bucket = "tf-state-prod"
remote_state.tf:
terraform {
backend "gcs" {
prefix = "terraform/state"
}
}
then, you can run the init. So for example, for dev this would look like:
$ terraform init --backend-config=config/dev.config
then, you can create a workspace for the environment:
$ terraform workspace new dev
With this approach, you can use a single set of templates (you can in fact configure dynamic variables based on the current workspace).

Answer 2

What you could do (we have a project with a similar setup with a different cloud provider), is:
use infra-common as a module
instead of working with .tfvar files per environment, use a separate root module per environment which invokes infra-common as sub-module.
Your folder structure could look like:
project
|-- dev
| `-- main.tf
|-- modules
| `-- infra-common
| |-- main.tf
| `-- variables.tf
|-- test
| `-- main.tf
`-- prod
`-- main.tf
dev/main.tf
terraform {
backend "gcs" {
bucket = "tf-state-dev"
prefix = "terraform/state"
}
}
module "stage" {
source = "../modules/infra-common"
env = "dev"
some_var = "value"
}
prod/main.tf
terraform {
backend "gcs" {
bucket = "tf-state-prod"
prefix = "terraform/state"
}
}
module "stage" {
source = "../modules/infra-common"
env = "prod"
some_var = "value"
}