google_compute_backend_bucket with FORCE_CACHE_ALL automatically setting max_ttl to 0, causing 400 from API

[apottere]

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Terraform Version

$ terraform -v
Terraform v1.0.11
on darwin_amd64
+ provider registry.terraform.io/hashicorp/google v4.1.0
+ provider registry.terraform.io/hashicorp/google-beta v4.1.0
+ provider registry.terraform.io/hashicorp/random v3.1.0

Affected Resource(s)

• google_compute_backend_bucket

Terraform Configuration Files

resource "google_compute_backend_bucket" "bucket" {
  name        = "..."
  description = "..."
  bucket_name = "..."

  enable_cdn = true
  cdn_policy {
    cache_mode                   = "FORCE_CACHE_ALL"
    signed_url_cache_max_age_sec = 0
    default_ttl                  = 0
    client_ttl                   = 0
    serve_while_stale            = 0
  }
}

Debug Output

(partially redacted with ...)

[...]

PUT /compute/v1/projects/.../global/backendBuckets/...?alt=json HTTP/1.1
Host: compute.googleapis.com
User-Agent: Terraform/1.0.11 (+https://www.terraform.io) Terraform-Plugin-SDK/2.5.0 terraform-provider-google/4.1.0
Content-Length: 342
Content-Type: application/json
Accept-Encoding: gzip

{
 "bucketName": "...",
 "cdnPolicy": {
  "cacheMode": "FORCE_CACHE_ALL",
  "clientTtl": 0,
  "defaultTtl": 0,
  "maxTtl": 0,
  "negativeCaching": false,
  "serveWhileStale": 0,
  "signedUrlCacheMaxAgeSec": 0
 },
 "description": "...",
 "enableCdn": true,
 "name": "..."
}

[...]

HTTP/2.0 400 Bad Request
Alt-Svc: ...
Cache-Control: private
Content-Type: application/json; charset=UTF-8
Date: Mon, 15 Nov 2021 17:38:22 GMT
Server: ESF
Vary: Origin
Vary: X-Origin
Vary: Referer
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-Xss-Protection: 0

{
  "error": {
    "code": 400,
    "message": "Invalid value for field 'resource.cdnPolicy.cacheMode': 'FORCE_CACHE_ALL'. max_ttl must be specified with CACHE_ALL_STATIC cache_mode only.",
    "errors": [
      {
        "message": "Invalid value for field 'resource.cdnPolicy.cacheMode': 'FORCE_CACHE_ALL'. max_ttl must be specified with CACHE_ALL_STATIC cache_mode only.",
        "domain": "global",
        "reason": "invalid"
      }
    ]
  }
}

Expected Behavior

Provider should omit the max_ttl field from the API request since it's not present in the terraform source.

Actual Behavior

Provider adds max_ttl=0 automatically, which causes the google API to return a 400 because max_ttl cannot be specified with FORCE_CACHE_ALL

Steps to Reproduce

1. terraform apply

Important Factoids

I also tried manually removing the "max_ttl" field from the terraform state, but it was just re-added when applying.

[github-actions]

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