// cache the namespace, so manually added echo.Configs can be a part of it
	b.namespaces[cfg.Namespace.Prefix()] = cfg.Namespace

	targetClusters := b.clusters
	if cfg.Cluster != nil {
		targetClusters = cluster.Clusters{cfg.Cluster}
	}

	deployedTo := 0
	for idx, c := range targetClusters {
		ec, ok := c.(echo.Cluster)
		if !ok {

	var targetClusters []cluster.Cluster
	if watchLocalNamespace {
		// when configured to watch istiod local namespace, secrets go to the external cluster
		// and primary clusters
		targetClusters = i.ctx.AllClusters().Primaries()
	} else {
		// when configured to watch istiod config namespace, secrets go to config clusters
		targetClusters = i.ctx.AllClusters().Configs()
	}

		if err != nil {
			return nil, err
		}
		targetCluster, err := parseClusterIndex(parts[1])
		if err != nil {
			return nil, err
		}
		if _, ok := out[sourceCluster]; ok {
			return nil, fmt.Errorf("multiple mappings for source cluster %d", sourceCluster)
		}
		out[sourceCluster] = targetCluster
	}
	return out, nil
}