Added --hetzner-image-id flag as suggested in #14

Author: JonasProgrammer

README.md

@@ -77,10 +77,22 @@ $ docker-machine create \
   some-machine
 ```
 
+### Using a snapshot
+
+Assuming your snapshot ID is `424242`:
+```bash
+$ docker-machine create \
+  --driver hetzner \
+  --hetzner-api-token=QJhoRT38JfAUO037PWJ5Zt9iAABIxdxdh4gPqNkUGKIrUMd6I3cPIsfKozI513sy \
+  --hetzner-image-id=424242 \
+  some-machine
+```
+
 ## Options
 
 - `--hetzner-api-token`: **required**. Your project-specific access token for the Hetzner Cloud API.
-- `--hetzner-image`: The name of the Hetzner Cloud image to use, see [Images API](https://docs.hetzner.cloud/#resources-images-get) for how to get a list  (defaults to `ubuntu-16.04`).
+- `--hetzner-image`: The name of the Hetzner Cloud image to use, see [Images API](https://docs.hetzner.cloud/#resources-images-get) for how to get a list (defaults to `ubuntu-16.04`).
+- `--hetzner-image-id`: The id of the Hetzner cloud image (or snapshot) to use, see [Images API](https://docs.hetzner.cloud/#resources-images-get) for how to get a list (mutually excludes `--hetzner-image`).
 - `--hetzner-server-type`: The type of the Hetzner Cloud server, see [Server Types API](https://docs.hetzner.cloud/#resources-server-types-get) for how to get a list (defaults to `cx11`).
 - `--hetzner-server-location`: The location to create the server in, see [Locations API](https://docs.hetzner.cloud/#resources-locations-get) for how to get a list.
 **NOTICE: Beware that Hetzner does not reject invalid location names at the time of writing this; instead, a seemingly random location is chosen. Double check both the option value's
@@ -110,7 +122,8 @@ was used during creation.
 | CLI option                          | Environment variable              | Default                    |
 | ----------------------------------- | --------------------------------- | -------------------------- |
 | **`--hetzner-api-token`**           | `HETZNER_API_TOKEN`               | -                          |
-| `--hetzner-image `                  | `HETZNER_IMAGE_IMAGE`             | `ubuntu-16.04`             |
+| `--hetzner-image`                   | `HETZNER_IMAGE_IMAGE`             | `ubuntu-16.04`             |
+| `--hetzner-image-id`                | `HETZNER_IMAGE_IMAGE_ID`          | -                          |
 | `--hetzner-server-type`             | `HETZNER_TYPE`                    | `cx11`                     |
 | `--hetzner-server-location`         | `HETZNER_LOCATION`                | - *(let Hetzner choose)*   |
 | `--hetzner-existing-key-path`       | `HETZNER_EXISTING_KEY_PATH`       | - *(generate new keypair)* |

driver.go

@@ -24,6 +24,7 @@ type Driver struct {
 
 	AccessToken    string
 	Image          string
+	ImageID        int
 	cachedImage    *hcloud.Image
 	Type           string
 	cachedType     *hcloud.ServerType
@@ -45,6 +46,7 @@ const (
 
 	flagAPIToken  = "hetzner-api-token"
 	flagImage     = "hetzner-image"
+	flagImageID   = "hetzner-image-id"
 	flagType      = "hetzner-server-type"
 	flagLocation  = "hetzner-server-location"
 	flagExKeyID   = "hetzner-existing-key-id"
@@ -83,6 +85,11 @@ func (d *Driver) GetCreateFlags() []mcnflag.Flag {
 			Usage:  "Image to use for server creation",
 			Value:  defaultImage,
 		},
+		mcnflag.IntFlag{
+			EnvVar: "HETZNER_IMAGE_ID",
+			Name:   flagImageID,
+			Usage:  "Image to use for server creation",
+		},
 		mcnflag.StringFlag{
 			EnvVar: "HETZNER_TYPE",
 			Name:   flagType,
@@ -119,6 +126,7 @@ func (d *Driver) GetCreateFlags() []mcnflag.Flag {
 func (d *Driver) SetConfigFromFlags(opts drivers.DriverOptions) error {
 	d.AccessToken = opts.String(flagAPIToken)
 	d.Image = opts.String(flagImage)
+	d.ImageID = opts.Int(flagImageID)
 	d.Location = opts.String(flagLocation)
 	d.Type = opts.String(flagType)
 	d.KeyID = opts.Int(flagExKeyID)
@@ -131,6 +139,11 @@ func (d *Driver) SetConfigFromFlags(opts drivers.DriverOptions) error {
 	if d.AccessToken == "" {
 		return errors.Errorf("hetzner requires --%v to be set", flagAPIToken)
 	}
+
+	if d.ImageID != 0 && d.Image != defaultImage {
+		return errors.Errorf("--%v and --%v are mutually exclusive", flagImage, flagImageID)
+	}
+
 	return nil
 }
 
@@ -466,10 +479,21 @@ func (d *Driver) getImage() (*hcloud.Image, error) {
 		return d.cachedImage, nil
 	}
 
-	image, _, err := d.getClient().Image.GetByName(context.Background(), d.Image)
-	if err != nil {
-		return image, errors.Wrap(err, "could not get image by name")
+	var image *hcloud.Image
+	var err error
+
+	if d.ImageID != 0 {
+		image, _, err = d.getClient().Image.GetByID(context.Background(), d.ImageID)
+		if err != nil {
+			return image, errors.Wrap(err, fmt.Sprintf("could not get image by id %v", d.ImageID))
+		}
+	} else {
+		image, _, err = d.getClient().Image.GetByName(context.Background(), d.Image)
+		if err != nil {
+			return image, errors.Wrap(err, fmt.Sprintf("could not get image by name %v", d.Image))
+		}
 	}
+
 	d.cachedImage = image
 	return image, nil
 }