https://www.elastic.co/guide/en/elasticsearch/reference/2.3/modules-node.html#client-node
Node
Any time that you start an instance of Elasticsearch, you are starting a node. A collection of connected nodes is called a cluster. If you are running a single node of Elasticsearch, then you have a cluster of one node.
你启动一个实例以后，一个node就在运行了。一个集群中包含多个互相可通信的node。如果只有一个node，那这就是一个单节点的集群。
Every node in the cluster can handle HTTP and Transport traffic by default. The transport layer is used exclusively（唯一地） for communication between nodes and between nodes and the Java TransportClient
; the HTTP layer is used only by external REST clients.
集群中的每个节点默认都是可以处理http和transport通信的。transport层被用作节点和节点之间以及节点和java transportclient之间的通信。；http层被用作外部的rest客户端。
All nodes know about all the other nodes in the cluster and can forward client requests to the appropriate node. Besides that, each node serves one or more purpose:
所有节点知道其他节点中的其他节点，并且可以把客户端发的请求转发到适当的节点。除此之外，每个节点服务一个或多个目标：
Master-eligible node
A node that has node.master set to true (default), which makes it eligible to be elected （当选）as the masternode, which controls the cluster.
node.master 选项被设置为true，被当选为masternode，可以控制集群。
Data node
A node that has node.data set to true (default). Data nodes hold data and perform data related operations such as CRUD, search, and aggregations.
node.data 被设置为true，数据节点处理数据相关的操作如crud，查询和分组。
Client node
A client node has both node.master and node.data set to false. It can neither hold data nor become the master node. It behaves as a “smart router” and is used to forward cluster-level requests to the master node and data-related requests (such as search) to the appropriate data nodes.
client 节点，node.master 和node.data都被设置为false。它不会被用作处理数据和变成一个master node。它被的工作室”智能分发“ 和被用作转发集群级别的请求到主节点和数据相关的操作到合适的data node
Tribe部落 node
A tribe node, configured via the tribe.*
settings, is a special type of client node that can connect to multiple clusters and perform search and other operations across all connected clusters.
特殊的客户端节点，可以连接到多个集群，并且处理其他的操作通过所有连接上的集群。
By default a node is both a master-eligible node and a data node. This is very convenient for small clusters but, as the cluster grows, it becomes important to consider separating dedicated master-eligible nodes from dedicated data nodes.
默认情况下，一个节点既是master也是datanode。对于小集群来说很方便。 伴随着集群的增长，要考虑吧datanode和masternode分离开。
<b>Coordinating node</b>
Requests like search requests or bulk-indexing requests may involve（涉及） data held on different data nodes. A search request, for example, is executed in two phases（阶段） which are coordinated by the node which receives the client request — the coordinating node.In the scatter（分散） phase, the coordinating node forwards the request to the data nodes which hold the data. Each data node executes the request locally and returns its results to the coordinating node. In the gather phase, the coordinating node reduces each data node’s results into a single global resultset.This means that a client node needs to have enough memory and CPU in order to deal with the gather phase.
请求比如说搜索请求，或者多索引请求可以可能涉及到的数据抓取自不同的节点。一个搜索请求，例如说，执行到2个阶段接收到请求的节点-coordinatenode 定位.a、在分散阶段，coordinate node 转发请求到保存着数据的data.node。每个data.node在本地执行请求，并返回结果到coordinate node,b、在合并阶段，coordinate.node 合并每个节点的结果到一个全局的结果集。这以为着client node 需要足够的内存和cpu来处理合并阶段。
