https://github.com/datastax/java-driver/java-driver-core: A driver for Apache Cassandra(R) 2.1+ that works exclusively with the Cassandra Query Language version 3 (CQL3) and Cassandra's native protocol versions 3 and above.
  • Various (DataStax) 
/*
 * Copyright DataStax, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.datastax.oss.driver.api.core.metadata;

import com.datastax.oss.driver.api.core.loadbalancing.LoadBalancingPolicy;
import com.datastax.oss.driver.internal.core.metadata.TopologyEvent;
import java.net.InetSocketAddress;


The state of a node, as viewed from the driver. 
/** The state of a node, as viewed from the driver. */
public enum NodeState {
  
The driver has never tried to connect to the node, nor received any topology events about it.

This happens when nodes are first added to the cluster, and will persist if your LoadBalancingPolicy decides to ignore them. Since the driver does not connect to them, the only way it can assess their states is from topology events. 
/**
   * The driver has never tried to connect to the node, nor received any topology events about it.
   *
   * <p>This happens when nodes are first added to the cluster, and will persist if your {@link
   * LoadBalancingPolicy} decides to ignore them. Since the driver does not connect to them, the
   * only way it can assess their states is from topology events.
   */
  UNKNOWN,
  
A node is considered up in either of the following situations:

    
  
  • the driver has at least one active connection to the node.
  
  • the driver is not actively trying to connect to the node (because it's ignored by the LoadBalancingPolicy), but it has received a topology event indicating that the node is up. 


/**
   * A node is considered up in either of the following situations:
   *
   * <ul>
   *   <li>the driver has at least one active connection to the node.
   *   <li>the driver is not actively trying to connect to the node (because it's ignored by the
   *       {@link LoadBalancingPolicy}), but it has received a topology event indicating that the
   *       node is up.
   * </ul>
   */
  UP,
  
A node is considered down in either of the following situations:

    
  
  • the driver has lost all connections to the node (and is currently trying to reconnect).
  
  • the driver is not actively trying to connect to the node (because it's ignored by the LoadBalancingPolicy), but it has received a topology event indicating that the node is down. 


/**
   * A node is considered down in either of the following situations:
   *
   * <ul>
   *   <li>the driver has lost all connections to the node (and is currently trying to reconnect).
   *   <li>the driver is not actively trying to connect to the node (because it's ignored by the
   *       {@link LoadBalancingPolicy}), but it has received a topology event indicating that the
   *       node is down.
   * </ul>
   */
  DOWN,
  
The node was forced down externally, the driver will never try to reconnect to it, whatever the LoadBalancingPolicy says. 
This is used for edge error cases, for example when the driver detects that it's trying to connect to a node that does not belong to the Cassandra cluster (e.g. a wrong address was provided in the contact points). It can also be triggered explicitly by components (for example a custom load balancing policy) that want to limit the number of nodes that the driver connects to. 
/**
   * The node was forced down externally, the driver will never try to reconnect to it, whatever the
   * {@link LoadBalancingPolicy} says.
   *
   * <p>This is used for edge error cases, for example when the driver detects that it's trying to
   * connect to a node that does not belong to the Cassandra cluster (e.g. a wrong address was
   * provided in the contact points). It can also be {@link
   * TopologyEvent#forceDown(InetSocketAddress) triggered explicitly} by components (for example a
   * custom load balancing policy) that want to limit the number of nodes that the driver connects
   * to.
   */
  FORCED_DOWN,
}