allow 0 for negative_caching_policy.ttl

[edwardmedia]

Fixes hashicorp/terraform-provider-google#9805

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

compute: fixed a bug where `negative_caching_policy` cannot be set always revalidate on `google_compute_backend_service`

[modular-magician]

Hello! I am a robot who works on Magic Modules PRs.

I have detected that you are a community contributor, so your PR will be assigned to someone with a commit-bit on this repo for initial review.

Thanks for your contribution! A human will be with you soon.

@c2thorn, please review this PR or find an appropriate assignee.

[edwardmedia]

This behavior is only applied in global Backend Service ( regional Backend Service does not support cdn policy https://cloud.google.com/cdn#section-6 )

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 1 insertion(+), 1 deletion(-))
Terraform Beta: Diff ( 2 files changed, 3 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 1 insertion(+), 1 deletion(-))

[ljybar]

"0" still doesn't work for negative_caching_policy.ttl
google v3.80.0
google-beta v3.80.0

Code part:

resource "google_compute_backend_service" "ocom-ci-dev1-app-backsvc1" {
  name = "ocom-ci-dev1-app-backsvc1"
  provider = google-beta
  load_balancing_scheme = "EXTERNAL"
  backend {
    balancing_mode = "UTILIZATION"
    max_utilization = "0.9"
    group = google_compute_instance_group.ocom-ci-dev1-app-group1.id
  }
  backend {
    balancing_mode = "UTILIZATION"
    max_utilization = "0.9"
    group = google_compute_instance_group.ocom-ci-dev1-app-group2.id
  }
  health_checks = [
    google_compute_http_health_check.ocom-ci-dev1-app-hc1.id
  ]
  port_name = "http"
  protocol = "HTTP"
  timeout_sec = "86400"
  connection_draining_timeout_sec = "600"
  log_config {
    enable = true
    sample_rate = 1
  }
  enable_cdn = true
  cdn_policy {
    cache_mode = "USE_ORIGIN_HEADERS"
    cache_key_policy {
      include_host = true
      include_protocol = true
      include_query_string = true
    }
    serve_while_stale = 86400
    signed_url_cache_max_age_sec = 3600
    negative_caching = true
    negative_caching_policy {
      code = 501
      ttl = 0
    }
    negative_caching_policy {
      code = 404
      ttl = 0
    }
    negative_caching_policy {
      code = 451
      ttl = 0
    }
}

Error example:

`google_compute_backend_service.ocom-ci-dev1-app-backsvc1: Creating...

Error: Error creating BackendService: googleapi: Error 400: Invalid value for field 'resource.cdnPolicy.negativeCachingPolicy[0]': '{  "code": 501}'. Code and ttl must be specified in NegativeCachingPolicy., invalid

  on main.tf line 2785, in resource "google_compute_backend_service" "ocom-ci-dev1-app-backsvc1":
2785: resource "google_compute_backend_service" "ocom-ci-dev1-app-backsvc1" {
`

if the problem has already been resolved, what do I need to do to make the object creation work for me?

[c2thorn]

@ljybar This fix has not been released yet, and should be a part of v3.81.
If you need/want to try out the fix now, you could build the provider at this commit: f17f748 (#9821)