improve documentation for IGM/RIGM

third_party/terraform/website/docs/guides/version_3_upgrade.html.markdown

@@ -641,11 +641,45 @@ resource "google_compute_instance_group_manager" "my_igm" {
 ### `update_strategy` has been replaced by `update_policy`
 
 To allow much greater control over the updates happening to instance groups
-`update_strategy` has been replaced by `update_policy`. The previous
-functionality to determine if instance should be replaced or restarted can be
-achieved using `update_policy.minimal_action`. For more details see the
+`update_strategy` has been replaced by `update_policy`. The functionality controlled by `update_strategy` is now controlled by a combination of `update_policy.type` and `update_policy.minimal_action`. `update_strategy = NONE` can be achieved with `type = OPPORTUNISTIC`. The previous values of `RESTART` and `REPLACE` were both `PROACTIVE` types implicitly previously but can now be controlled explicitly.
+
+For more details see the
 [official guide](https://cloud.google.com/compute/docs/instance-groups/rolling-out-updates-to-managed-instance-groups).
 
+### Old Config
+
+```hcl
+resource "google_compute_instance_group_manager" "my_igm" {
+    name               = "my-igm"
+    zone               = "us-central1-c"
+    base_instance_name = "igm"
+
+    instance_template = "${google_compute_instance_template.my_tmpl.self_link}"
+
+    update_strategy   = "NONE"
+}
+```
+
+### New Config
+
+```hcl
+resource "google_compute_instance_group_manager" "my_igm" {
+    name               = "my-igm"
+    zone               = "us-central1-c"
+    base_instance_name = "igm"
+
+    version {
+        name = "prod"
+        instance_template = "${google_compute_instance_template.my_tmpl.self_link}"
+    }
+
+    update_policy {
+      minimal_action = "RESTART"
+      type           = "OPPORTUNISTIC"
+    }
+}
+```
+
 ## Resource: `google_compute_instance_template`
 
 ### At least one of `enable_secure_boot`, `enable_vtpm`, or `enable_integrity_monitoring` is now required on `google_compute_instance_template.shielded_instance_config`

third_party/terraform/website/docs/r/compute_instance_group_manager.html.markdown

@@ -149,9 +149,9 @@ update_policy {
 }
 ```
 
-* `minimal_action` - (Required) - Minimal action to be taken on an instance. Valid values are `"RESTART"`, `"REPLACE"`
+* `minimal_action` - (Required) - Minimal action to be taken on an instance. You can specify either `RESTART` to restart existing instances or `REPLACE` to delete and create new instances from the target template. If you specify a `RESTART`, the Updater will attempt to perform that action only. However, if the Updater determines that the minimal action you specify is not enough to perform the update, it might perform a more disruptive action.
 
-* `type` - (Required) - The type of update. Valid values are `"OPPORTUNISTIC"`, `"PROACTIVE"`
+* `type` - (Required) - The type of update process. You can specify either `PROACTIVE` so that the instance group manager proactively executes actions in order to bring instances to their target versions or `OPPORTUNISTIC` so that no action is proactively executed but the update will be performed as part of other actions (for example, resizes or recreateInstances calls).
 
 * `max_surge_fixed` - (Optional), The maximum number of instances that can be created above the specified targetSize during the update process. Conflicts with `max_surge_percent`. If neither is set, defaults to 1
 

third_party/terraform/website/docs/r/compute_region_instance_group_manager.html.markdown

@@ -152,9 +152,9 @@ update_policy {
 }
 ```
 
-* `minimal_action` - (Required) - Minimal action to be taken on an instance. Valid values are `"RESTART"`, `"REPLACE"`
+* `minimal_action` - (Required) - Minimal action to be taken on an instance. You can specify either `RESTART` to restart existing instances or `REPLACE` to delete and create new instances from the target template. If you specify a `RESTART`, the Updater will attempt to perform that action only. However, if the Updater determines that the minimal action you specify is not enough to perform the update, it might perform a more disruptive action.
 
-* `type` - (Required) - The type of update. Valid values are `"OPPORTUNISTIC"`, `"PROACTIVE"`
+* `type` - (Required) - The type of update process. You can specify either `PROACTIVE` so that the instance group manager proactively executes actions in order to bring instances to their target versions or `OPPORTUNISTIC` so that no action is proactively executed but the update will be performed as part of other actions (for example, resizes or recreateInstances calls).
 
 * `instance_redistribution_type` - (Optional) - The instance redistribution policy for regional managed instance groups. Valid values are: `"PROACTIVE"`, `"NONE"`. If `PROACTIVE` (default), the group attempts to maintain an even distribution of VM instances across zones in the region. If `NONE`, proactive redistribution is disabled.