method ListClusters not supported in server-side client

Error message

method ListClusters not supported in server-side client

What it means

ListClusters is another unimplemented stub in the server-side clientset; the controller operates on a single known cluster, so enumerating all clusters is not supported. Any call returns this error immediately.

Source

Thrown at cmd/kops-controller/pkg/controllerclientset/clientset.go:97

// VFSContext returns a VFSContext.
func (c *client) VFSContext() *vfs.VFSContext {
	return c.vfsContext
}

// CreateCluster creates a cluster
func (c *client) CreateCluster(ctx context.Context, cluster *kops.Cluster) (*kops.Cluster, error) {
	return nil, fmt.Errorf("method CreateCluster not supported in server-side client")
}

// UpdateCluster updates a cluster
func (c *client) UpdateCluster(ctx context.Context, cluster *kops.Cluster, status *kops.ClusterStatus) (*kops.Cluster, error) {
	return nil, fmt.Errorf("method UpdateCluster not supported in server-side client")
}

// ListClusters returns all clusters
func (c *client) ListClusters(ctx context.Context, options metav1.ListOptions) (*kops.ClusterList, error) {
	return nil, fmt.Errorf("method ListClusters not supported in server-side client")
}

// ConfigBaseFor returns the vfs path where we will read configuration information from
func (c *client) ConfigBaseFor(cluster *kops.Cluster) (vfs.Path, error) {
	return nil, fmt.Errorf("method ConfigBaseFor not supported in server-side client")
}

// InstanceGroupsFor returns the InstanceGroupInterface bound to the namespace for a particular Cluster
func (c *client) InstanceGroupsFor(cluster *kops.Cluster) kopsinternalversion.InstanceGroupInterface {
	clusterName := cluster.Name
	if clusterName != c.clusterName {
		klog.Fatalf("clientset bound to cluster %q, got cluster %q", c.clusterName, clusterName)
	}

	return newInstanceGroups(c.vfsContext, cluster, c.clusterBasePath)
}

// AddonsFor returns the client for addon objects for a particular Cluster

View on GitHub (pinned to 4c8573c808)

Solutions

Use the cluster name the controller was configured with (c.clusterName) and call GetCluster instead of listing
Run the listing logic via the `kops` CLI or a VFS-backed clientset outside the controller
If multi-cluster support is needed, deploy one controller per cluster rather than listing

Example fix

// before
clusters, err := client.ListClusters(ctx, metav1.ListOptions{})
// after: use the single configured cluster
cluster, err := client.GetCluster(ctx, client.ConfigBaseFor(&kops.Cluster{Name: os.Getenv("KOPS_CLUSTER_NAME")}))

Defensive patterns

Strategy: fallback

Validate before calling

if clusterName == "" {
  return errors.New("KOPS_CLUSTER_NAME must be set; server-side clientset cannot list clusters")
}

Try / catch

clusters, err := client.ListClusters(ctx, metav1.ListOptions{})
if err != nil && strings.Contains(err.Error(), "ListClusters not supported") {
  // fallback: fetch the single configured cluster
  one, gerr := client.GetCluster(ctx, clusterPath)
  ...
}

Prevention

Controllers are single-cluster scoped: always use the configured cluster name
Do not port `kops get clusters` logic into kops-controller
Run one controller instance per cluster instead of enumerating

When it happens

Trigger: Calling client.ListClusters(ctx, metav1.ListOptions{}) from code shared with the CLI, or iterating all clusters (e.g. a multi-cluster reporting or mutation routine) while running inside kops-controller.

Common situations: Reusing kops toolbox/CLI code that lists clusters; porting `kops get clusters` style logic into the controller binary.

Related errors

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/e959c18bc7724d5f. Report an issue: GitHub.