Fix Autoscaling for worker nodes with invalid ProviderID

cluster-autoscaler/cloudprovider/hetzner/hetzner_manager.go

@@ -256,9 +256,19 @@ func (m *hetznerManager) addNodeToDrainingPool(node *apiv1.Node) (*hetznerNodeGr
 	return m.nodeGroups[drainingNodePoolId], nil
 }
 
+func (m *hetznerManager) validProviderID(providerID string) bool {
+	return strings.HasPrefix(providerID, providerIDPrefix)
+}
+
 func (m *hetznerManager) serverForNode(node *apiv1.Node) (*hcloud.Server, error) {
 	var nodeIdOrName string
 	if node.Spec.ProviderID != "" {
+		if !m.validProviderID(node.Spec.ProviderID) {
+			// This cluster-autoscaler provider only handles Hetzner Cloud servers.
+			// Any other provider ID prefix is invalid, and we return no server. Returning an error here breaks hybrid
+			// clusters with nodes from Hetzner Cloud & Robot (or other providers).
+			return nil, nil
+		}
 		nodeIdOrName = strings.TrimPrefix(node.Spec.ProviderID, providerIDPrefix)
 	} else {
 		nodeIdOrName = node.Name

cluster-autoscaler/cloudprovider/hetzner/hetzner_servers_cache.go

@@ -18,7 +18,6 @@ package hetzner
 
 import (
 	"context"
-	"errors"
 	"strconv"
 	"sync"
 	"time"
@@ -136,7 +135,8 @@ func (m *serversCache) getServer(nodeIdOrName string) (*hcloud.Server, error) {
 		}
 	}
 
-	return nil, errors.New("server not found")
+	// return nil if server not found
+	return nil, nil
 }
 
 func (m *serversCache) getServersByNodeGroupName(nodeGroup string) ([]*hcloud.Server, error) {

cluster-autoscaler/cloudprovider/hetzner/hetzner_servers_cache_test.go

@@ -70,6 +70,7 @@ func TestServersCache(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "test2", foundservers.Name)
 
-	_, err = c.getServer("test3")
-	require.Error(t, err)
+	server, err := c.getServer("test3")
+	require.Nil(t, server)
+	require.NoError(t, err)
 }