Default compute backend buckets TTLs dynamically

[d10i]

Instead of always defaulting default_ttl, max_ttl and client_ttl, only do it when it makes sense, depending on the value of cache_mode.

Fixes https://github.com/hashicorp/terraform-provider-google/issues/10622.

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

• [X] 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).
• [X] Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• [X] 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).
• [X] Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

compute: fixed a bug when `cache_mode` is set to USE_ORIGIN_HEADERS on `google_compute_backend_bucket`

[modular-magician]

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

[d10i]

See issue comment for more context on this draft PR.

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 2 files changed, 97 insertions(+), 2 deletions(-)) Terraform Beta: Diff ( 3 files changed, 115 insertions(+), 20 deletions(-)) TF Validator: Diff ( 1 file changed, 55 insertions(+), 2 deletions(-))

[rileykarson]

@ndmckinley I'm fairly underwater on reviews. Mind picking this up, given you're already engaged in discussions on the linked issue? Thanks!

[nat-henderson]

I think this is right. Let's run the tests - if they pass, I'm good to merge.

/gcbrun

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 3 files changed, 137 insertions(+), 42 deletions(-)) Terraform Beta: Diff ( 2 files changed, 97 insertions(+), 2 deletions(-)) TF Validator: Diff ( 1 file changed, 55 insertions(+), 2 deletions(-))

[nat-henderson]

The test seems to fail.

    provider_test.go:270: Step 5/12 error: After applying this test step, the plan was not empty.                                                                                                                                              
        stdout:                                                                                                        
                                                           
                                                           
        An execution plan has been generated and is shown below.
        Resource actions are indicated with the following symbols:
          ~ update in-place                                
                                                           
        Terraform will perform the following actions:
                                                           
          # google_compute_backend_bucket.foobar will be updated in-place
          ~ resource "google_compute_backend_bucket" "foobar" {
                bucket_name             = "tf-test-uzanb9zfqs"
                creation_timestamp      = "2021-12-13T10:49:57.235-08:00"
                custom_response_headers = []
                enable_cdn              = true
                id                      = "projects/personal-graphite-testing/global/backendBuckets/tf-test-bx9p7rfjnj"
                name                    = "tf-test-bx9p7rfjnj"
                project                 = "personal-graphite-testing"
                self_link               = "https://www.googleapis.com/compute/v1/projects/personal-graphite-testing/global/backendBuckets/tf-test-bx9p7rfjnj"
                                                           
              ~ cdn_policy {                               
                    cache_mode                   = "CACHE_ALL_STATIC"
                  ~ client_ttl                   = 3600 -> 0
                  ~ default_ttl                  = 3600 -> 0
                    max_ttl                      = 86400
                    negative_caching             = true
                    serve_while_stale            = 0
                    signed_url_cache_max_age_sec = 0
                                                           
                    negative_caching_policy {
                        code = 404
                        ttl  = 0
                    }                                      
                }                                          
            }                                              
                         

[d10i]

Yeah @ndmckinley, see this issue comment for more context.

[nat-henderson]

I think the problem is related to GetOk.

c, cdnPolicyOk := d.GetOk("cdn_policy")

unfortunately, cdnPolicyOk will be false if the user doesn't set cdn_policy - but only on initial create. Afterwards, it will be true, and c will be 0. This is an annoying detail of Terraform's internal serialization logic, which we can't really work around.

If I'm right, the linked issue is not fixable this way. Very frustrating! We probably won't merge a PR that breaks existing tests or examples, even if it improves behavior for a different set of users, so you'd need to find another way to express this. I'm not really sure what that way would be... I don't currently know how to fix this so it works for everyone.

[IchordeDionysos]

What's the status here? Is there anything we could do to speed up the fix? ☺️