google_compute_region_backend_service should not have enable_cdn argument, as Regional Load Balancers don't support Cloud CDN

[mikewirth]

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Terraform Version & Provider Version(s)

Terraform v1.9.8
on darwin_arm64

• provider registry.terraform.io/hashicorp/google v6.12.0
• provider registry.terraform.io/hashicorp/google-beta v6.12.0

Affected Resource(s)

google_compute_region_backend_service

Terraform Configuration

resource "google_compute_region_backend_service" "test" {
  name                  = "test"
  region                = "europe-west1"
  protocol              = "HTTP"
  port_name             = "http"
  load_balancing_scheme = "EXTERNAL_MANAGED"
  timeout_sec           = 30

  enable_cdn = true

  backend {
    group           = google_compute_region_network_endpoint_group.test_neg.id
    capacity_scaler = 1.0
  }
}

Debug Output

Error: Error updating RegionBackendService "projects/myproject/regions/europe-west1/backendServices/test": googleapi: Error 400: Invalid value for field 'resource.enableCDN': 'true'. Enable CDN is not allowed for regional EXTERNAL_MANAGED backend service with HTTP(S) protocol., invalid

Expected Behavior

The arguments enable_cdn and cdn_policy should not be present on google_compute_region_backend_service, as the Regional External Application Load Balancer does not support Cloud CDN.

Quote from the documentation:

Cloud CDN is supported with the global external Application Load Balancer and the classic Application Load Balancer.

Actual Behavior

The GCP API returns an error 400:

Error: Error updating RegionBackendService "projects/myproject/regions/europe-west1/backendServices/test": googleapi: Error 400: Invalid value for field 'resource.enableCDN': 'true'. Enable CDN is not allowed for regional EXTERNAL_MANAGED backend service with HTTP(S) protocol., invalid

Steps to reproduce

1. terraform apply

Important Factoids

No response

References

https://cloud.google.com/load-balancing/docs/load-balancing-overview
https://cloud.google.com/compute/docs/reference/rest/v1/regionBackendServices: The API documentation for the regionBackendService lists the parameter enableCDN, but also says:

If true, enables Cloud CDN for the backend service of a global external Application Load Balancer.