private Map<Integer, Integer> minReplication(DistributorNodeInfo distributorNodeInfo) {
        Map<Integer, Integer> replicationPerNodeIndex = new HashMap<>();
        for (StorageNode storageNode : distributorNodeInfo.getHostInfo().getDistributor().getStorageNodes()) {
            var currentValue = replicationPerNodeIndex.get(storageNode.getIndex());
            Integer minReplicationFactor = storageNode.getMinCurrentReplicationFactorOrNull();
            if (currentValue == null || (minReplicationFactor != null && minReplicationFactor < currentValue))
                replicationPerNodeIndex.put(storageNode.getIndex(), minReplicationFactor);
        }

        return replicationPerNodeIndex;
    }
Verifies that storage nodes and distributors are up (or retired).
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/NodeStateChangeChecker.java