code: public Observable<LifecycleState> addNode(final NetworkAddress hostname, final NetworkAddress alternate) {
          Node node = nodeBy(hostname);
          if (node != null) {
              LOGGER.debug("Node {} already registered, skipping.", hostname);
              return Observable.just(node.state());
          }
          return addNode(new CouchbaseNode(hostname, ctx, alternate));
      }
docs: Add a {@link Node} identified by its hostname.
  
  @param hostname the hostname of the node.
  @return the states of the node (most probably {@link LifecycleState#CONNECTED}).