etcd 是 CoreOS 团队发起的一个开源项目（Go 语言，其实很多这类项目都是 Go 语言实现的，只能说很强大），实现了分布式键值存储和服务发现，etcd 和 ZooKeeper/Consul 非常相似，都提供了类似的功能，以及 REST API 的访问操作，具有以下特点：
etcd 可以单个实例使用，也可以进行集群配置，因为很多项目都是以 etcd 作为服务发现，比如 CoreOS 和 Kubernetes，所以，下面我们使用 Docker 简单搭建一下 etcd 集群。
1. 主机安装
如果不使用 Docker 的话，etcd 在主机上安装，也非常简单。
Linux 安装命令：
$ curl -L https://github.com/coreos/etcd/releases/download/v3.3.0-rc.0/etcd-v3.3.0-rc.0-linux-amd64.tar.gz -o etcd-v3.3.0-rc.0-linux-amd64.tar.gz &&
sudo tar xzvf etcd-v3.3.0-rc.0-linux-amd64.tar.gz &&
cd etcd-v3.3.0-rc.0-linux-amd64 &&
sudo cp etcd* /usr/local/bin/
其实就是将编译后的二进制文件，拷贝到/usr/local/bin/目录，各个版本的二进制文件，可以从 https://github.com/coreos/etcd/releases/ 中查找下载。
Mac OS 安装命令：
$ ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" < /dev/null 2> /dev/null
$ brew install etcd
执行下面命令，查看 etcd 是否安装成功：
$ etcd --version
etcd Version: 3.2.12
Git SHA: GitNotFound
Go Version: go1.9.2
Go OS/Arch: darwin/amd64
2. 集群搭建
搭建 etcd 集群，需要借助下 Docker Machine 创建三个 Docker 主机，命令：
$ docker-machine create -d virtualbox manager1 &&
docker-machine create -d virtualbox worker1 &&
docker-machine create -d virtualbox worker2
$ docker-machine ls
NAME ACTIVE DRIVER STATE URL SWARM DOCKER ERRORS
manager1 - virtualbox Running tcp://192.168.99.100:2376 v17.11.0-ce
worker1 - virtualbox Running tcp://192.168.99.101:2376 v17.11.0-ce
worker2 - virtualbox Running tcp://192.168.99.102:2376 v17.11.0-ce
为防止 Docker 主机中垃取官方镜像，速度慢的问题，我们还需要将 etcd 镜像打包推送到私有仓库中，命令：
$ docker tag quay.io/coreos/etcd 192.168.99.1:5000/quay.io/coreos/etcd:latest &&
docker push 192.168.99.1:5000/quay.io/coreos/etcd:latest &&
docker pull 192.168.99.1:5000/quay.io/coreos/etcd:latest
另外，还需要将私有仓库地址配置在 Docker 主机中，并重启三个 Docker 主机，具体配置参考：Docker 三剑客之 Docker Swarm
Docker 主机配置好之后，我们需要使用docker-machine ssh命令，分别进入三个 Docker 主机中，执行 Docker etcd 配置命令。
manager1 主机（node1 192.168.99.100）：
$ docker run -d --name etcd
-p 2379:2379
-p 2380:2380
--volume=etcd-data:/etcd-data
192.168.99.1:5000/quay.io/coreos/etcd
/usr/local/bin/etcd
--data-dir=/etcd-data --name node1
--initial-advertise-peer-urls http://192.168.99.100:2380 --listen-peer-urls http://0.0.0.0:2380
--advertise-client-urls http://192.168.99.100:2379 --listen-client-urls http://0.0.0.0:2379
--initial-cluster-state new
--initial-cluster-token docker-etcd
--initial-cluster node1=http://192.168.99.100:2380,node2=http://192.168.99.101:2380,node3=http://192.168.99.102:2380
worker1 主机（node2 192.168.99.101）：
$ docker run -d --name etcd
-p 2379:2379
-p 2380:2380
--volume=etcd-data:/etcd-data
192.168.99.1:5000/quay.io/coreos/etcd
/usr/local/bin/etcd
--data-dir=/etcd-data --name node2
--initial-advertise-peer-urls http://192.168.99.101:2380 --listen-peer-urls http://0.0.0.0:2380
--advertise-client-urls http://192.168.99.101:2379 --listen-client-urls http://0.0.0.0:2379
--initial-cluster-state new
--initial-cluster-token docker-etcd
--initial-cluster node1=http://192.168.99.100:2380,node2=http://192.168.99.101:2380,node3=http://192.168.99.102:2380
worker2 主机（node1 192.168.99.102）：
$ docker run -d --name etcd
-p 2379:2379
-p 2380:2380
--volume=etcd-data:/etcd-data
192.168.99.1:5000/quay.io/coreos/etcd
/usr/local/bin/etcd
--data-dir=/etcd-data --name node3
--initial-advertise-peer-urls http://192.168.99.102:2380 --listen-peer-urls http://0.0.0.0:2380
--advertise-client-urls http://192.168.99.102:2379 --listen-client-urls http://0.0.0.0:2379
--initial-cluster-state existing
--initial-cluster-token docker-etcd
--initial-cluster node1=http://192.168.99.100:2380,node2=http://192.168.99.101:2380,node3=http://192.168.99.102:2380
先来说明下 etcd 各个配置参数的意思（参考自 etcd 使用入门）：
- –name：节点名称，默认为 default。
- –data-dir：服务运行数据保存的路径，默认为${name}.etcd。
- –snapshot-count：指定有多少事务（transaction）被提交时，触发截取快照保存到磁盘。
- –heartbeat-interval：leader 多久发送一次心跳到 followers。默认值是 100ms。
- –eletion-timeout：重新投票的超时时间，如果 follow 在该时间间隔没有收到心跳包，会触发重新投票，默认为 1000 ms。
- –listen-peer-urls：和同伴通信的地址，比如http://ip:2380，如果有多个，使用逗号分隔。需要所有节点都能够访问，所以不要使用 localhost！
- –listen-client-urls：对外提供服务的地址：比如http://ip:2379,http://127.0.0.1:2379，客户端会连接到这里和 etcd 交互。
- –advertise-client-urls：对外公告的该节点客户端监听地址，这个值会告诉集群中其他节点。
- –initial-advertise-peer-urls：该节点同伴监听地址，这个值会告诉集群中其他节点。
- –initial-cluster：集群中所有节点的信息，格式为node1=http://ip1:2380,node2=http://ip2:2380,…，注意：这里的 node1 是节点的 –name 指定的名字；后面的 ip1:2380 是 –initial-advertise-peer-urls 指定的值。
- –initial-cluster-state：新建集群的时候，这个值为 new；假如已经存在的集群，这个值为 existing。
- –initial-cluster-token：创建集群的 token，这个值每个集群保持唯一。这样的话，如果你要重新创建集群，即使配置和之前一样，也会再次生成新的集群和节点 uuid；否则会导致多个集群之间的冲突，造成未知的错误。
上述配置也可以设置配置文件，默认为/etc/etcd/etcd.conf。
我们可以使用docker ps，查看 Docker etcd 是否配置成功：
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
463380d23dfe 192.168.99.1:5000/quay.io/coreos/etcd "/usr/local/bin/et..." 2 hours ago Up 2 hours 0.0.0.0:2379-2380->2379-2380/tcp etcd
然后进入其中一个 Docker 主机：
$ docker exec -it etcd bin/sh
执行下面命令（查看集群成员）：
$ etcdctl member list
773d30c9fc6640b4: name=node2 peerURLs=http://192.168.99.101:2380 clientURLs=http://192.168.99.101:2379 isLeader=true
b2b0bca2e0cfcc19: name=node3 peerURLs=http://192.168.99.102:2380 clientURLs=http://192.168.99.102:2379 isLeader=false
c88e2cccbb287a01: name=node1 peerURLs=http://192.168.99.100:2380 clientURLs=http://192.168.99.100:2379 isLeader=false
可以看到，集群里面有三个成员，并且node2为管理员，node1和node3为普通成员。
etcdctl 是 ectd 的客户端命令工具（也是 go 语言实现），里面封装了 etcd 的 REST API 执行命令，方便我们进行操作 etcd，后面再列出 etcdctl 的命令详细说明。
上面命令的 etcd API 版本为 2.0，我们可以手动设置版本为 3.0，命令：
$ export ETCDCTL_API=3 && /usr/local/bin/etcdctl put foo bar
OK
部分命令和执行结果还是和 2.0 版本，有很多不同的，比如同是查看集群成员，3.0 版本的执行结果：
$ etcdctl member list
773d30c9fc6640b4, started, node2, http://192.168.99.101:2380, http://192.168.99.101:2379
b2b0bca2e0cfcc19, started, node3, http://192.168.99.102:2380, http://192.168.99.102:2379
c88e2cccbb287a01, started, node1, http://192.168.99.100:2380, http://192.168.99.100:2379
好了，我们现在再演示一种情况，就是从集群中移除一个节点，然后再把它添加到集群中，为演示 etcd 中使用 Raft 算法，我们将node2管理节点，作为操作对象。
我们在随便一个主机 etcd 容器中（node2除外），执行成员移除集群命令（必须使用 ID，使用别名会报错）：
$ etcdctl member remove 773d30c9fc6640b4
Member 773d30c9fc6640b4 removed from cluster f84185fa5f91bdf6
我们再执行下查看集群成员命令（v2 版本）：
$ etcdctl member list
b2b0bca2e0cfcc19: name=node3 peerURLs=http://192.168.99.102:2380 clientURLs=http://192.168.99.102:2379 isLeader=true
c88e2cccbb287a01: name=node1 peerURLs=http://192.168.99.100:2380 clientURLs=http://192.168.99.100:2379 isLeader=false
会发现node2管理节点被移除集群了，并且通过 Raft 算法，node3被推举为管理节点。
在将node2节点重新加入集群之前，我们需要执行下面命令：
$ etcdctl member add node2 --peer-urls="http://192.168.99.101:2380"
Member 22b0de6ffcd98f00 added to cluster f84185fa5f91bdf6
ETCD_NAME="node2"
ETCD_INITIAL_CLUSTER="node2=http://192.168.99.101:2380,node3=http://192.168.99.102:2380,node1=http://192.168.99.100:2380"
ETCD_INITIAL_CLUSTER_STATE="existing"
可以看到，ETCD_INITIAL_CLUSTER_STATE 值为existing，也就是我们配置的–initial-cluster-state参数。
我们再执行下查看集群成员命令（v2 版本）：
$ etcdctl member list
22b0de6ffcd98f00[unstarted]: peerURLs=http://192.168.99.101:2380
b2b0bca2e0cfcc19: name=node3 peerURLs=http://192.168.99.102:2380 clientURLs=http://192.168.99.102:2379 isLeader=true
c88e2cccbb287a01: name=node1 peerURLs=http://192.168.99.100:2380 clientURLs=http://192.168.99.100:2379 isLeader=false
会发现22b0de6ffcd98f00成员状态变为了unstarted。
我们在node2节点，执行 Docker etcd 集群配置命令：
$ docker run -d --name etcd
-p 2379:2379
-p 2380:2380
--volume=etcd-data:/etcd-data
192.168.99.1:5000/quay.io/coreos/etcd
/usr/local/bin/etcd
--data-dir=/etcd-data --name node2
--initial-advertise-peer-urls http://192.168.99.101:2380 --listen-peer-urls http://0.0.0.0:2380
--advertise-client-urls http://192.168.99.101:2379 --listen-client-urls http://0.0.0.0:2379
--initial-cluster-state existing
--initial-cluster-token docker-etcd
--initial-cluster node1=http://192.168.99.100:2380,node2=http://192.168.99.101:2380,node3=http://192.168.99.102:2380
结果并不像我们想要的那样成功，执行查看日志：
$ docker logs etcd
2017-12-25 08:19:30.160967 I | etcdmain: etcd Version: 3.2.12
2017-12-25 08:19:30.161062 I | etcdmain: Git SHA: b19dae0
2017-12-25 08:19:30.161082 I | etcdmain: Go Version: go1.8.5
2017-12-25 08:19:30.161092 I | etcdmain: Go OS/Arch: linux/amd64
2017-12-25 08:19:30.161105 I | etcdmain: setting maximum number of CPUs to 1, total number of available CPUs is 1
2017-12-25 08:19:30.161144 N | etcdmain: the server is already initialized as member before, starting as etcd member...
2017-12-25 08:19:30.161195 I | embed: listening for peers on http://0.0.0.0:2380
2017-12-25 08:19:30.161232 I | embed: listening for client requests on 0.0.0.0:2379
2017-12-25 08:19:30.165269 I | etcdserver: name = node2
2017-12-25 08:19:30.165317 I | etcdserver: data dir = /etcd-data
2017-12-25 08:19:30.165335 I | etcdserver: member dir = /etcd-data/member
2017-12-25 08:19:30.165347 I | etcdserver: heartbeat = 100ms
2017-12-25 08:19:30.165358 I | etcdserver: election = 1000ms
2017-12-25 08:19:30.165369 I | etcdserver: snapshot count = 100000
2017-12-25 08:19:30.165385 I | etcdserver: advertise client URLs = http://192.168.99.101:2379
2017-12-25 08:19:30.165593 I | etcdserver: restarting member 773d30c9fc6640b4 in cluster f84185fa5f91bdf6 at commit index 14
2017-12-25 08:19:30.165627 I | raft: 773d30c9fc6640b4 became follower at term 11
2017-12-25 08:19:30.165647 I | raft: newRaft 773d30c9fc6640b4 [peers: [], term: 11, commit: 14, applied: 0, lastindex: 14, lastterm: 11]
2017-12-25 08:19:30.169277 W | auth: simple token is not cryptographically signed
2017-12-25 08:19:30.170424 I | etcdserver: starting server... [version: 3.2.12, cluster version: to_be_decided]
2017-12-25 08:19:30.171732 I | etcdserver/membership: added member 773d30c9fc6640b4 [http://192.168.99.101:2380] to cluster f84185fa5f91bdf6
2017-12-25 08:19:30.171845 I | etcdserver/membership: added member c88e2cccbb287a01 [http://192.168.99.100:2380] to cluster f84185fa5f91bdf6
2017-12-25 08:19:30.171877 I | rafthttp: starting peer c88e2cccbb287a01...
2017-12-25 08:19:30.171902 I | rafthttp: started HTTP pipelining with peer c88e2cccbb287a01
2017-12-25 08:19:30.175264 I | rafthttp: started peer c88e2cccbb287a01
2017-12-25 08:19:30.175339 I | rafthttp: added peer c88e2cccbb287a01
2017-12-25 08:19:30.178326 I | etcdserver/membership: added member cbd7fa8d01297113 [http://192.168.99.102:2380] to cluster f84185fa5f91bdf6
2017-12-25 08:19:30.178383 I | rafthttp: starting peer cbd7fa8d01297113...
2017-12-25 08:19:30.178410 I | rafthttp: started HTTP pipelining with peer cbd7fa8d01297113
2017-12-25 08:19:30.179794 I | rafthttp: started peer cbd7fa8d01297113
2017-12-25 08:19:30.179835 I | rafthttp: added peer cbd7fa8d01297113
2017-12-25 08:19:30.180062 N | etcdserver/membership: set the initial cluster version to 3.0
2017-12-25 08:19:30.180132 I | etcdserver/api: enabled capabilities for version 3.0
2017-12-25 08:19:30.180255 N | etcdserver/membership: updated the cluster version from 3.0 to 3.2
2017-12-25 08:19:30.180430 I | etcdserver/api: enabled capabilities for version 3.2
2017-12-25 08:19:30.183979 I | rafthttp: started streaming with peer c88e2cccbb287a01 (writer)
2017-12-25 08:19:30.184139 I | rafthttp: started streaming with peer c88e2cccbb287a01 (writer)
2017-12-25 08:19:30.184232 I | rafthttp: started streaming with peer c88e2cccbb287a01 (stream MsgApp v2 reader)
2017-12-25 08:19:30.185142 I | rafthttp: started streaming with peer c88e2cccbb287a01 (stream Message reader)
2017-12-25 08:19:30.186518 I | etcdserver/membership: removed member cbd7fa8d01297113 from cluster f84185fa5f91bdf6
2017-12-25 08:19:30.186573 I | rafthttp: stopping peer cbd7fa8d01297113...
2017-12-25 08:19:30.186614 I | rafthttp: started streaming with peer cbd7fa8d01297113 (writer)
2017-12-25 08:19:30.186786 I | rafthttp: stopped streaming with peer cbd7fa8d01297113 (writer)
2017-12-25 08:19:30.186815 I | rafthttp: started streaming with peer cbd7fa8d01297113 (writer)
2017-12-25 08:19:30.186831 I | rafthttp: stopped streaming with peer cbd7fa8d01297113 (writer)
2017-12-25 08:19:30.186876 I | rafthttp: started streaming with peer cbd7fa8d01297113 (stream MsgApp v2 reader)
2017-12-25 08:19:30.187224 I | rafthttp: started streaming with peer cbd7fa8d01297113 (stream Message reader)
2017-12-25 08:19:30.187647 I | rafthttp: stopped HTTP pipelining with peer cbd7fa8d01297113
2017-12-25 08:19:30.187682 I | rafthttp: stopped streaming with peer cbd7fa8d01297113 (stream MsgApp v2 reader)
2017-12-25 08:19:30.187873 I | rafthttp: stopped streaming with peer cbd7fa8d01297113 (stream Message reader)
2017-12-25 08:19:30.187895 I | rafthttp: stopped peer cbd7fa8d01297113
2017-12-25 08:19:30.187911 I | rafthttp: removed peer cbd7fa8d01297113
2017-12-25 08:19:30.188034 I | etcdserver/membership: added member b2b0bca2e0cfcc19 [http://192.168.99.102:2380] to cluster f84185fa5f91bdf6
2017-12-25 08:19:30.188059 I | rafthttp: starting peer b2b0bca2e0cfcc19...
2017-12-25 08:19:30.188075 I | rafthttp: started HTTP pipelining with peer b2b0bca2e0cfcc19
2017-12-25 08:19:30.188510 I | rafthttp: started peer b2b0bca2e0cfcc19
2017-12-25 08:19:30.188533 I | rafthttp: added peer b2b0bca2e0cfcc19
2017-12-25 08:19:30.188795 I | etcdserver/membership: removed member 773d30c9fc6640b4 from cluster f84185fa5f91bdf6
2017-12-25 08:19:30.193643 I | rafthttp: started streaming with peer b2b0bca2e0cfcc19 (writer)
2017-12-25 08:19:30.193730 I | rafthttp: started streaming with peer b2b0bca2e0cfcc19 (writer)
2017-12-25 08:19:30.193797 I | rafthttp: started streaming with peer b2b0bca2e0cfcc19 (stream MsgApp v2 reader)
2017-12-25 08:19:30.194782 I | rafthttp: started streaming with peer b2b0bca2e0cfcc19 (stream Message reader)
2017-12-25 08:19:30.195663 I | raft: 773d30c9fc6640b4 [term: 11] received a MsgHeartbeat message with higher term from b2b0bca2e0cfcc19 [term: 12]
2017-12-25 08:19:30.195716 I | raft: 773d30c9fc6640b4 became follower at term 12
2017-12-25 08:19:30.195736 I | raft: raft.node: 773d30c9fc6640b4 elected leader b2b0bca2e0cfcc19 at term 12
2017-12-25 08:19:30.196617 E | rafthttp: streaming request ignored (ID mismatch got 22b0de6ffcd98f00 want 773d30c9fc6640b4)
2017-12-25 08:19:30.197064 E | rafthttp: streaming request ignored (ID mismatch got 22b0de6ffcd98f00 want 773d30c9fc6640b4)
2017-12-25 08:19:30.197846 E | rafthttp: streaming request ignored (ID mismatch got 22b0de6ffcd98f00 want 773d30c9fc6640b4)
2017-12-25 08:19:30.198242 E | rafthttp: streaming request ignored (ID mismatch got 22b0de6ffcd98f00 want 773d30c9fc6640b4)
2017-12-25 08:19:30.201771 E | etcdserver: the member has been permanently removed from the cluster
2017-12-25 08:19:30.202060 I | etcdserver: the data-dir used by this member must be removed.
2017-12-25 08:19:30.202307 E | etcdserver: publish error: etcdserver: request cancelled
2017-12-25 08:19:30.202338 I | etcdserver: aborting publish because server is stopped
2017-12-25 08:19:30.202364 I | rafthttp: stopping peer b2b0bca2e0cfcc19...
2017-12-25 08:19:30.202482 I | rafthttp: stopped streaming with peer b2b0bca2e0cfcc19 (writer)
2017-12-25 08:19:30.202504 I | rafthttp: stopped streaming with peer b2b0bca2e0cfcc19 (writer)
2017-12-25 08:19:30.204143 I | rafthttp: stopped HTTP pipelining with peer b2b0bca2e0cfcc19
2017-12-25 08:19:30.204186 I | rafthttp: stopped streaming with peer b2b0bca2e0cfcc19 (stream MsgApp v2 reader)
2017-12-25 08:19:30.204205 I | rafthttp: stopped streaming with peer b2b0bca2e0cfcc19 (stream Message reader)
2017-12-25 08:19:30.204217 I | rafthttp: stopped peer b2b0bca2e0cfcc19
2017-12-25 08:19:30.204228 I | rafthttp: stopping peer c88e2cccbb287a01...
2017-12-25 08:19:30.204241 I | rafthttp: stopped streaming with peer c88e2cccbb287a01 (writer)
2017-12-25 08:19:30.204255 I | rafthttp: stopped streaming with peer c88e2cccbb287a01 (writer)
2017-12-25 08:19:30.204824 I | rafthttp: stopped HTTP pipelining with peer c88e2cccbb287a01
2017-12-25 08:19:30.204860 I | rafthttp: stopped streaming with peer c88e2cccbb287a01 (stream MsgApp v2 reader)
2017-12-25 08:19:30.204878 I | rafthttp: stopped streaming with peer c88e2cccbb287a01 (stream Message reader)
2017-12-25 08:19:30.204891 I | rafthttp: stopped peer c88e2cccbb287a01
这么长的日志，说明啥问题呢，就是说我们虽然重新执行的 etcd 创建命令，但因为读取之前配置文件的关系，etcd 会恢复之前的集群成员，但之前的集群节点已经被移除了，所以集群节点就一直处于停止状态。
怎么解决呢？很简单，就是将我们之前创建的etcd-data数据卷轴删掉，命令：
$ docker volume ls
DRIVER VOLUME NAME
local etcd-data
$ docker volume rm etcd-data
etcd-data
然后，再在node2节点，重新执行 Docker etcd 集群配置命令（上面），会发现执行是成功的。
我们再执行下查看集群成员命令（v2 版本）：
$ etcdctl member list
22b0de6ffcd98f00: name=node2 peerURLs=http://192.168.99.101:2380 clientURLs=http://192.168.99.101:2379 isLeader=false
b2b0bca2e0cfcc19: name=node3 peerURLs=http://192.168.99.102:2380 clientURLs=http://192.168.99.102:2379 isLeader=true
c88e2cccbb287a01: name=node1 peerURLs=http://192.168.99.100:2380 clientURLs=http://192.168.99.100:2379 isLeader=false
3. API 操作
etcd REST API 被用于键值操作和集群成员操作，这边就简单说几个，详细的 API 查看附录说明。
3.1 键值管理
设置键值命令：
$ curl http://127.0.0.1:2379/v2/keys/hello -XPUT -d value="hello world"
{"action":"set","node":{"key":"/hello","value":"hello world","modifiedIndex":17,"createdIndex":17}}
查看键值命令：
$ curl http://127.0.0.1:2379/v2/keys/hello
{"action":"get","node":{"key":"/hello","value":"hello world","modifiedIndex":17,"createdIndex":17}}
删除键值命令：
$ curl http://127.0.0.1:2379/v2/keys/hello -XDELETE
{"action":"delete","node":{"key":"/hello","modifiedIndex":19,"createdIndex":17},"prevNode":{"key":"/hello","value":"hello world","modifiedIndex":17,"createdIndex":17}}
3.2 成员管理
列出集群中的所有成员：
$ curl http://127.0.0.1:2379/v2/members
{"members":[{"id":"22b0de6ffcd98f00","name":"node2","peerURLs":["http://192.168.99.101:2380"],"clientURLs":["http://192.168.99.101:2379"]},{"id":"b2b0bca2e0cfcc19","name":"node3","peerURLs":["http://192.168.99.102:2380"],"clientURLs":["http://192.168.99.102:2379"]},{"id":"c88e2cccbb287a01","name":"node1","peerURLs":["http://192.168.99.100:2380"],"clientURLs":["http://192.168.99.100:2379"]}]}
查看当前节点是否为管理节点：
$ curl http://127.0.0.1:2379/v2/stats/leader
{"leader":"b2b0bca2e0cfcc19","followers":{"22b0de6ffcd98f00":{"latency":{"current":0.001051,"average":0.0029195000000000002,"standardDeviation":0.001646769458667484,"minimum":0.001051,"maximum":0.006367},"counts":{"fail":0,"success":10}},"c88e2cccbb287a01":{"latency":{"current":0.000868,"average":0.0022389999999999997,"standardDeviation":0.0011402923601720172,"minimum":0.000868,"maximum":0.004725},"counts":{"fail":0,"success":12}}}}
查看当前节点信息：
$ curl http://127.0.0.1:2379/v2/stats/self
{"name":"node3","id":"b2b0bca2e0cfcc19","state":"StateLeader","startTime":"2017-12-25T06:00:28.803429523Z","leaderInfo":{"leader":"b2b0bca2e0cfcc19","uptime":"36m45.45263851s","startTime":"2017-12-25T08:13:02.103896843Z"},"recvAppendRequestCnt":6,"sendAppendRequestCnt":22}
查看集群状态：
$ curl http://127.0.0.1:2379/v2/stats/store
{"getsSuccess":9,"getsFail":4,"setsSuccess":9,"setsFail":0,"deleteSuccess":3,"deleteFail":0,"updateSuccess":0,"updateFail":0,"createSuccess":7,"createFail":0,"compareAndSwapSuccess":0,"compareAndSwapFail":0,"compareAndDeleteSuccess":0,"compareAndDeleteFail":0,"expireCount":0,"watchers":0}
当然也可以通过 API 添加和删除集群成员。
4. API 说明和 etcdctl 命令说明
etcd REST API 说明（v2 版本）：
更多 API 请查看：https://coreos.com/etcd/docs/latest/v2/api.html 和 https://coreos.com/etcd/docs/latest/v2/members_api.html
etcdctl 命令说明：
