add better documentation

Author: tuunit

docs/supported-platforms.md

@@ -20,7 +20,7 @@ Ignition is currently supported for the following platforms:
 * [Hetzner Cloud] (`hetzner`) - Ignition will read its configuration from the instance userdata. Cloud SSH keys are handled separately.
 * [Microsoft Hyper-V] (`hyperv`) - Ignition will read its configuration from the `ignition.config` key in pool 0 of the Hyper-V Data Exchange Service (KVP). Values are limited to approximately 1 KiB of text, so Ignition can also read and concatenate multiple keys named `ignition.config.0`, `ignition.config.1`, and so on.
 * [IBM Cloud] (`ibmcloud`) - Ignition will read its configuration from the instance userdata. Cloud SSH keys are handled separately.
-* [IONOS Cloud] (`ionoscloud`) - Ignition will read its configuration from the instance userdata. Cloud SSH keys are handled separately.
+* [IONOS Cloud] (`ionoscloud`) - Ignition will read its configuration from the instance user-data. Cloud SSH keys are handled separately. Per default the user-data is looked up on the root partition in `/var/lib/cloud/seed/nocloud/user-data`. The root partition is detected by the label `ROOT` which can be customized using the environment variable `IGNITION_CONFIG_ROOT_LABEL`.
 * [KubeVirt] (`kubevirt`) - Ignition will read its configuration from the instance userdata via config drive. Cloud SSH keys are handled separately.
 * Bare Metal (`metal`) - Use the `ignition.config.url` kernel parameter to provide a URL to the configuration. The URL can use the `http://`, `https://`, `tftp://`, `s3://`, `arn:`, or `gs://` schemes to specify a remote config.
 * [Nutanix] (`nutanix`) - Ignition will read its configuration from the instance userdata via config drive. Cloud SSH keys are handled separately.

internal/providers/ionoscloud/ionoscloud.go

@@ -11,10 +11,16 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-
-// The IONOSCloud provider fetches configurations from the userdata available in
-// the injected file /var/lib/cloud/seed/nocloud/user-data.
+//
 // NOTE: This provider is still EXPERIMENTAL.
+//
+// The IONOS Cloud provider fetches the ignition config from the user-data
+// available in an injected file at /var/lib/cloud/seed/nocloud/user-data.
+// This file is created by the IONOS Cloud VM handler before the first boot
+// through the cloud init user data handling.
+//
+// User data with the directive #cloud-init will be ignored
+// See for more: https://docs.ionos.com/cloud/compute-services/compute-engine/how-tos/boot-cloud-init
 
 package ionoscloud