Add ability to call Cloud Functions and receive results

[dinvlad]

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Description

Cloud Functions API exposes projects.locations.functions.call method to synchronously invoke a function for testing purposes [1].

Having an ability to do that from inside a Terraform template would significantly raise extensibility of the provider, including an ability to:

• deploy some resources before they're supported by the provider
• configure some resources in a security context, where temporary credentials are created/stored in Secret Manager, and we'd like to avoid their storage in Terraform state

This would also mirror similar functionality in other providers and systems, e.g. aws_lambda_invocation or AWS::CloudFormation::CustomResource.

New or Affected Resource(s)

• google_cloudfunctions_function_call

Potential Terraform Configuration

data "google_cloudfunctions_function_call" "call" {
  project        = google_cloudfunctions_function.function.project
  region         = google_cloudfunctions_function.function.region
  cloud_function = google_cloudfunctions_function.function.name

  data = jsonencode({ hello = "world" })
}

locals {
  cloud_function_output = data.google_cloudfunctions_function_call.call.result
}

References

• [1] https://cloud.google.com/functions/docs/reference/rest/v1/projects.locations.functions/call
• b/274818221

[fishpen0]

See: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/lambda_invocation for the AWS equivalent.

This is often used for fetching data or resources terraform cannot natively support:

data "aws_lambda_invocation" "data_terraform_cant_get" {
  function_name = "myfunction"
}

output "mydata" {
  value = data.aws_lambda_invocation.data_terraform_cant_get.result
}

resource "other_resource" "other" {
  resource_argument = data.aws_lambda_invocation.data_terraform_cant_get.result
}

[SarahFrench]

Note from triage: Moving out of backlog due to prior art in the AWS provider, but the documentation for this new data source should warn that the Cloud Function shouldn't have side effects. This data source heavily depends on what the CF does.