public Collection<String> clusterIds() {
        synchronized (monitor) {
            return new HashSet<>(documentTypesPerCluster.keySet());
        }
    }
Context required to configure automatic reindexing for a given cluster controller cluster (for a given content cluster).

@author bjorncs
config-model/src/main/java/com/yahoo/vespa/model/admin/clustercontroller/ReindexingContext.java