`cloud_run_service`'s `container_concurrency` documentation is unclear

[jeremad]

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Terraform Version

Terraform v1.3.2
on linux_amd64
+ provider registry.terraform.io/hashicorp/google v4.40.0

Affected Resource(s)

• google_cloud_run_service

Terraform Configuration Files

resource "google_cloud_run_service" "service" {
  autogenerate_revision_name = true
  name = "service"
  location = "europe-west4"
  template {
    spec {
      containers {
        image = "gcr.io/project/service"
        resources {
          limits = {
            cpu    = "1000m"
            memory = "512Mi"
          }
        }
      }
      container_concurrency = 0
      timeout_seconds       = 30
    }
  }
}

Expected Behavior

The documentation about the container_concurrency setting is unclear. A value of 0 is documented as "thread-safe, the system should manage the max concurrency." However I did not find any reference to this behavior in the GCP documentation. There is no reference to thread safety there either.

Actual Behavior

The documentation has cloudy statements, without any reference to the GCP documentation.

The commit making this statement is 3 years old, (basically a old as Cloud Run), so my uneducated guess is that this feature has been removed. However I did not find evidence of that in the changelog.

References

https://cloud.google.com/run/docs/about-concurrency https://cloud.google.com/run/docs/reference/rest/v2/projects.locations.services#Service https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/cloud_run_service#container_concurrency https://cloud.google.com/run/docs/release-notes

b/272369303

[edwardmedia]

Here is what the provider's doc is based on. I guess the API has updated its part.

https://cloud.google.com/run/docs/reference/rest/v1/RevisionSpec

ContainerConcurrency specifies the maximum allowed in-flight (concurrent) requests per container instance of the Revision. If not specified, defaults to 80.

Note that it has a default (80) now. Adding a default to a field is a breaking-change

[txomon]

On top of this, from experimentation, it's not the same to set up 80 than to set up 0.

Setting up 0 will allow for cpu_limit < 1. However setting 80 explicitly will give an error if cpu_limit < 1. I have created a maybe related bug to this, #13361

[c2thorn]

Service team is planning to treat this as a documentation-only change while addressing the change in https://github.com/hashicorp/terraform-provider-google/issues/13361

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