Add docu for worker config sourceImage

docs/usage/usage.md

@@ -155,6 +155,7 @@ The worker configuration contains:
 
   If you attach the disk with `SCRATCH` type, either an `NVMe` interface or a `SCSI` interface must be specified.
   It is only meaningful to provide this volume interface if only `SCRATCH` data volumes are used.
+
 * Volume Encryption config that specifies values for `kmsKeyName` and `kmsKeyServiceAccountName`.
   * The `kmsKeyName` is the
   key name of the cloud kms disk encryption key and must be specified if CMEK disk encryption is needed.
@@ -166,6 +167,12 @@ The worker configuration contains:
     gcloud projects add-iam-policy-binding projectId --member
     serviceAccount:[email protected] --role roles/cloudkms.cryptoKeyEncrypterDecrypter
     ```
+
+* Setting a volume image with `volume.sourceImage`.
+  However, this parameter should only be used with particular caution.
+  For example Gardenlinux works with filesystem LABELs only and creating another disk form the very same image causes the LABELs to be duplicated.
+  See: https://github.com/gardener/gardener-extension-provider-gcp/issues/323
+
 * Service Account with their specified scopes, authorized for this worker.
 
   Service accounts created in advance that generate access tokens that can be accessed through the metadata server and used to authenticate applications on the instance.

pkg/apis/gcp/types_worker.go

@@ -42,6 +42,10 @@ type Volume struct {
 	Encryption *DiskEncryption
 
 	// SourceImage is the image to create this disk
+	// However, this parameter should only be used with particular caution.
+	// For example Gardenlinux works with filesystem LABELs only and creating
+	// another disk form the very same image causes the LABELs to be duplicated.
+	// See: https://github.com/gardener/gardener-extension-provider-gcp/issues/323
 	SourceImage *string
 }
 

pkg/apis/gcp/v1alpha1/types_worker.go

@@ -47,6 +47,10 @@ type Volume struct {
 	Encryption *DiskEncryption `json:"encryption,omitempty"`
 
 	// SourceImage is the image to create this disk
+	// However, this parameter should only be used with particular caution.
+	// For example Gardenlinux works with filesystem LABELs only and creating
+	// another disk form the very same image causes the LABELs to be duplicated.
+	// See: https://github.com/gardener/gardener-extension-provider-gcp/issues/323
 	// +optional
 	SourceImage *string `json:"sourceImage,omitempty"`
 }