Make elasticache_subnet_group subnet_ids essential

builtin/providers/aws/resource_aws_elasticache_subnet_group.go

@@ -32,8 +32,7 @@ func resourceAwsElasticacheSubnetGroup() *schema.Resource {
 			},
 			"subnet_ids": &schema.Schema{
 				Type:     schema.TypeSet,
-				Optional: true,
-				Computed: true,
+				Required: true,
 				Elem:     &schema.Schema{Type: schema.TypeString},
 				Set: func(v interface{}) int {
 					return hashcode.String(v.(string))

website/source/docs/providers/aws/r/elasticache_subnet_group.html.markdown

@@ -47,7 +47,7 @@ The following arguments are supported:
 * `description` – (Required) Description for the cache subnet group
 * `name` – (Required) Name for the cache subnet group. This value is stored as 
 a lowercase string
-* `subnet_ids` – (Optional) List of VPC Subnet IDs for the cache subnet group
+* `subnet_ids` – (Required) List of VPC Subnet IDs for the cache subnet group
 
 ## Attributes Reference