Enable running infracost against a terraform.tfstate file

[digitalronin]

To get costs of an existing infrastructure setup, we need to run something like:

terraform init
infracost --tfdir .

So infracost does a terraform plan internally, and then uses the output of that to generate a report. Alternatively, we can do the terraform plan manually, and then supply the output to infracost.

Either way is quite slow.

All of the information required to report on existing infrastructure will be in the terraform.tfstate JSON file for the project, so if it were possible to run something like:

infracost --terraform-statefile=/path/to/my/project/terraform.tfstate

This could enable cost reports to be generated much more quickly - I'd guess a few seconds rather than several minutes, since it shouldn't be necessary to run terraform init beforehand either.

For many use-cases, this may not be an issue, but in my particular case, with 200+ terraform projects to analyse, it makes a big difference, and I imagine some others will be in a similar situation.

[ctrlaltdev]

Bump for that issue - I'm using TerraGrunt and split my infra in a lot of modules and the work around needed are quite painful. Using the tfstate would really help.

[enribd]

Since separating the infrastructure in several tfstates is a best practice in Terraform, it could be nice to process a set of tfstates instead of just one. Also reading them from cloud object storages like a S3 bucket.

[aliscott]

#203 adds a --use-tfstate flag, which might solve this use case.

So in master you can run it with

# if running dev:
make run ARGS="--tfdir=/path/to/code --use-tfstate"

# if running binary:
infracost --tfdir=/path/to/code --use-tfstate

This still needs the terraform binary to run terraform show internally instead of directly reading the state file, which is the recommended way of interacting with the state (https://www.terraform.io/docs/state/index.html#format) and has the added benefit of working with both local and remote states.

From my testing, this is a lot faster than running terraform plan each time 😄

Let me know if this helps.

[ayr-ton]

I've created a new related issue here:

https://gitlab.com/infracost/infracost-gitlab-ci/-/issues/1

[alikhajeh1]

@ctrlaltdev / @enribd can you possibly try v0.7.2 (available on brew too), and see if the infracost --tfdir=/path/to/code --use-tfstate option is good enough to close this issue? It works with remote state. I haven't used TerraGrunt much so it would be great if you can create issues with any difficulties you hit with that.

Regarding several tfstates, maybe we can discuss it in #188 as it seems somewhat related.

[ctrlaltdev]

@alikhajeh1 It works fine!
Just used on a couple of modules and I get a nice output back!

Regarding terragrunt, I'll open an issue for that.

[alikhajeh1]

@ctrlaltdev thanks for creating #224, given the interest in that, I've put it at the top of the todo pile in https://github.com/infracost/infracost/projects/2

Closing this issue, new issues can be created for leftovers.