@Override
    public void shutdown() {
        for (ScheduledFuture<?> future : new ScheduledFuture<?>[] {
                discoveryFuture.get(), healthCheckFuture.get()
        }) {
            if (future != null && !future.isDone() && !future.isCancelled()) {
                future.cancel(true);
            }
        }
    }
Discovers nodes in the same cluster by querying against
{@code system.clusters} table.
clickhouse-client/src/main/java/com/clickhouse/client/ClickHouseNodes.java