OnHostMaintenance, googlecompute updating documenation , additional option for validation and setting defaults

builder/googlecompute/config.go

@@ -93,13 +93,23 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 	if c.ImageDescription == "" {
 		c.ImageDescription = "Created by Packer"
 	}
-	// Possible values:
-	//   "MIGRATE"
-	//   "TERMINATE"
-	if c.OnHostMaintenance == "" {
+	// Setting OnHostMaintenance Correct Defaults
+	//   "MIGRATE" : Possible if Preemptible is false
+	//   "TERMINATE": Posssible if Preemptible is true
+	if c.OnHostMaintenance == "" && c.Preemptible {
 		c.OnHostMaintenance = "MIGRATE"
 	}
 
+	if c.OnHostMaintenance == "" && !c.Preemptible {
+		c.OnHostMaintenance = "TERMINATE"
+	}
+
+	// Make sure user sets a valid value for on_host_maintenance option
+	if !(c.OnHostMaintenance == "MIGRATE" || c.OnHostMaintenance == "TERMINATE") {
+		errs = packer.MultiErrorAppend(errs,
+			errors.New("on_host_maintenance must be one of MIGRATE or TERMINATE."))
+	}
+
 	if c.ImageName == "" {
 		img, err := interpolate.Render("packer-{{timestamp}}", nil)
 		if err != nil {

builder/googlecompute/config_test.go

@@ -117,7 +117,7 @@ func TestConfigPrepare(t *testing.T) {
 		{
 			"on_host_maintenance",
 			"SO VERY BAD",
-			false,
+			true,
 		},
 		{
 			"preemptible",

website/source/docs/builders/googlecompute.html.md

@@ -178,6 +178,13 @@ builder.
     `use_internal_ip` must be true if this property is true.
 
 -   `preemptible` (boolean) - If true, launch a preembtible instance.
+-   'on_host_maintenance' (string) - Sets Host Maintenance Option
+     valid strings "MIGRATE" and "TERMINATE" please see
+     [GCE Instance Scheduling Options](https://cloud.google.com/compute/docs/instances/setting-instance-scheduling-options)
+     Not all machine_type in google support MIGRATE (machines with gpu)
+     also preemptiblity will impact available options
+     - preemptible == true , defaults to TERMINATE
+     - preemptible == false , defaults to MIGRATE
 
 -   `region` (string) - The region in which to launch the instance. Defaults to
     to the region hosting the specified `zone`.