google_compute_backend_service: Disabling 'serve_while_stale' not persisting

[QuentinMoss]

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Terraform Version

v1.0.2

Affected Resource(s)

• google_compute_backend_service

Terraform Configuration Files

Module code for CDN

....
      signed_url_cache_max_age_sec = lookup(local.safe_cdn_policy, "signed_url_cache_max_age_sec", var.cache_key_policy == null ? null : 0)
      default_ttl                  = lookup(local.safe_cdn_policy, "default_ttl", null)
      max_ttl                      = lookup(local.safe_cdn_policy, "max_ttl", null)
      client_ttl                   = lookup(local.safe_cdn_policy, "client_ttl", null)
      cache_mode                   = lookup(local.safe_cdn_policy, "cache_mode", "USE_ORIGIN_HEADERS")
      serve_while_stale            = lookup(local.safe_cdn_policy, "serve_while_stale", 0)
      # Negative caching appears to not be supported in the provider. This needs to be disabled manually to persist.
      negative_caching = lookup(local.safe_cdn_policy, "negative_caching", null)

      dynamic "negative_caching_policy" {
        for_each = coalesce(var.negative_caching_policies, [])
        content {
          code = lookup(negative_caching_policy.value, "code", null)
          ttl  = lookup(negative_caching_policy.value, "ttl", null)
        }
      }
    }
  }

Resource:

module "issue-example-backend-services" {
  source = "../../modules/gce_backend_services"
  name   = "issue_example"
  cdn    = true

  cdn_policy = {
    serve_while_stale = 0
  }
  cache_key_policy = {
    include_host         = true
    include_protocol     = true
    include_query_string = true
  }

  clusters = [
    {
      node_pool = module.issue_example.node_pool
    }
  ]
  ....

Debug Output

Expected Behavior

In a situation where you want to disable 'serve_while_stale' by default, a value of 0 or null does not persist

  ~ resource "google_compute_backend_service" "default" {
        id                              = "srecluster-policy-bot"
        name                            = "srecluster-policy-bot"
        # (15 unchanged attributes hidden)


      ~ cdn_policy {
          ~ serve_while_stale            = 86400 -> 0
            # (6 unchanged attributes hidden)

            # (1 unchanged block hidden)
        }

        # (2 unchanged blocks hidden)
    }

Actual Behavior

The settings displayed in the plan output are not actually modified in state once executed, and the changes will be planned each time you run 'terraform plan'

Steps to Reproduce

1. Configure a backend_service with CDN enabled, set serve_while_stale to 0, run apply twice and notice it will plan the same changes each time.

Important Factoids

References

• #0000

[QuentinMoss]

This is fixed in 3.74.0 - apparently the provider didn't support these values as they were not GA (?)

[github-actions]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.