managed instance group update_policy conflict on required variables

[jsumali]

TL;DR

On terraform-google-modules/vm/google//modules/mig, we're unable to set update_policy since all surge and unavailable parameters are required, but the underlying resources say that only one or the other (fixed or percent) should be used.

Expected behavior

This should be valid:

 update_policy             = [{
   type                            = "PROACTIVE"
   instance_redistribution_type    = "PROACTIVE"
   minimal_action                  = "REPLACE"
   most_disruptive_allowed_action  = "REPLACE"
   replacement_method              = "RECREATE"
   max_surge_fixed                 = 3
   max_unavailable_fixed           = 0
   min_ready_sec                   = 60
 }]

Observed behavior

Error:

│ The given value is not suitable for module.web-mig.var.update_policy declared at .terraform/modules/web-mig/modules/mig/variables.tf:81,1-25: element 0:
│ attributes "max_surge_percent" and "max_unavailable_percent" are required.

If we also specify max_surge_percent and max_unavailable_percent, then we get the following errors:

 update_policy             = [{
   type                            = "PROACTIVE"
   instance_redistribution_type    = "PROACTIVE"
   minimal_action                  = "REPLACE"
   most_disruptive_allowed_action  = "REPLACE"
   replacement_method              = "RECREATE"
   max_surge_fixed                 = 3
   max_surge_percent               = 50
   max_unavailable_fixed           = 0
   max_unavailable_percent         = 0
   min_ready_sec                   = 60
 }]

│ "update_policy.0.max_unavailable_percent": conflicts with update_policy.0.max_unavailable_fixed
│ "update_policy.0.max_surge_fixed": conflicts with update_policy.0.max_surge_percent
│ "update_policy.0.max_surge_percent": conflicts with update_policy.0.max_surge_fixed
│ "update_policy.0.max_unavailable_fixed": conflicts with update_policy.0.max_unavailable_percent

Terraform Configuration

module "web-mig" {
  source = "terraform-google-modules/vm/google//modules/mig"
  instance_template = module.web-instance-template.self_link
  project_id        = var.project_id
  region            = var.region
  ###
  distribution_policy_zones = [var.zone]
  autoscaling_enabled       = true
  autoscaling_cpu           = [{ "target" = 0.76, predictive_method = "NONE" }]
  min_replicas              = var.web_public_min_replicas
  max_replicas              = var.web_public_max_replicas
  hostname                  = "${var.env_prefix}-web-mig"
  mig_name                  = "${var.env_prefix}-web-mig"
  named_ports               = [{ "name" = "http", "port" = 80 }]
 update_policy             = [{
   type                            = "PROACTIVE"
   instance_redistribution_type    = "PROACTIVE"
   minimal_action                  = "REPLACE"
   most_disruptive_allowed_action  = "REPLACE"
   replacement_method              = "RECREATE"
   max_surge_fixed                 = 3
   max_unavailable_fixed           = 0
   min_ready_sec                   = 60
 }]
}

### Terraform Version

```sh
$ terraform versio
n
Terraform v1.3.3
on darwin_amd64
+ provider registry.terraform.io/hashicorp/google v4.56.0
+ provider registry.terraform.io/hashicorp/google-beta v4.56.0
+ provider registry.terraform.io/hashicorp/kubernetes v2.18.1
+ provider registry.terraform.io/hashicorp/random v3.4.3

Additional information

No response