安装etcd

etcd是一个golang编写的分布式、高可用的一致性键值存储系统，用于提供可靠的分布式键值(key-value)存储、配置共享和服务发现等功能。etcd可以用于存储关键数据和实现分布式调度，在现代化的集群运行中能够起到关键性的作用。

etcd基于raft协议，通过复制日志文件的方式来保证数据的强一致性。在etcd之前，常用的是基于paxos协议的zookeeper。

安装etcd

CentOS

yum install -y etcd

启动

# 设置开机自启动
$ sudo systemctl enable etcd
# 启动etcd
$ sudo systemctl start etcd
# 查看etcd运行状态
$ sudo systemctl status etcd
● etcd.service - Etcd Server
   Loaded: loaded (/usr/lib/systemd/system/etcd.service; disabled; vendor preset: disabled)
   Active: active (running) since 二 2019-06-18 19:36:16 CST; 3s ago
 Main PID: 3188591 (etcd)
    Tasks: 33
   Memory: 12.9M
   CGroup: /system.slice/etcd.service
           └─3188591 /usr/bin/etcd --name=default --data-dir=/var/lib/etcd/default.etcd --listen-client-urls=http://localhost:2379

6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: 8e9e05c52164694d received MsgVoteResp from 8e9e05c52164694d at term 2
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: 8e9e05c52164694d became leader at term 2
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: raft.node: 8e9e05c52164694d elected leader 8e9e05c52164694d at term 2
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: setting up the initial cluster version to 3.3
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: set the initial cluster version to 3.3
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: enabled capabilities for version 3.3
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: ready to serve client requests
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: published {Name:default ClientURLs:[http://localhost:2379]} to cluster cdf818194e3a8c32
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com systemd[1]: Started Etcd Server.
6月 18 19:36:16 103-18-41-sh-100-D10.yidian.com etcd[3188591]: serving insecure client requests on 127.0.0.1:2379, this is strongly discouraged!

systemd配置

从systemctl status etcd命令的输出可以看到，etcd的 systemd配置文件位于/usr/lib/systemd/system/etcd.service，该配置文件的内容如下：

$ cat /usr/lib/systemd/system/etcd.service
[Unit]
Description=Etcd Server
After=network.target
After=network-online.target
Wants=network-online.target

[Service]
Type=notify
WorkingDirectory=/var/lib/etcd/
EnvironmentFile=-/etc/etcd/etcd.conf
User=etcd
# set GOMAXPROCS to number of processors
ExecStart=/bin/bash -c "GOMAXPROCS=$(nproc) /usr/bin/etcd --name=\"${ETCD_NAME}\" --data-dir=\"${ETCD_DATA_DIR}\" --listen-client-urls=\"${ETCD_LISTEN_CLIENT_URLS}\""
Restart=on-failure
LimitNOFILE=65536

[Install]
WantedBy=multi-user.target

从上面的配置中可以看到，etcd的配置文件位于/etc/etcd/etcd.conf，如果我们想要修改某些配置项，可以编辑该文件。

远程访问

etcd安装完成后，默认只能本地访问，如果需要开启远程访问，还需要修改/etc/etcd/etcd.conf中的配置。例如，本实例中我安装etcd的机器IP是10.103.18.41，我尝试通过自己的机器远程访问10.103.18.41上安装的etcd的2379端口，结果访问被拒绝：

$ telnet 10.103.18.41 2379
Trying 10.103.18.41...
telnet: connect to address 10.103.18.41: Connection refused
telnet: Unable to connect to remote host

修改/etc/etcd/etcd.conf配置：

ETCD_LISTEN_CLIENT_URLS="http://10.103.18.41:2379,http://localhost:2379"

重启etcd

$ sudo systemctl restart etcd

再次远程访问：

$ telnet 10.103.18.41 2379
Trying 10.103.18.41...
Connected to 10.103.18.41.
Escape character is '^]'.

MacOS

brew install etcd

etcdctl

etcdctl 是官方提供的客户端程序。我们可以通过 etcdctl 相关命令实现如下操作：

1. 添加key-value并设置ttl

$ etcdctl set --ttl 5 key 'Hello World'
Hello World
$ etcdctl get key
Hello World
$ etcdctl get key
Error:  100: Key not found (/key) [7]

2.添加key-value

$ etcdctl set key 'Hello World'
Hello World
$ etcdctl update key 'Hello World2'
Hello World2

3.获取key-value

$ etcdctl get key
Hello World2

4.删除key-value

$ etcdctl rm key
PrevNode.Value: Hello World2
$ etcdctl get key
Error:  100: Key not found (/key) [10]

安装etcd webui

记得启动Etcd服务。
先安装node，git环境，然后clone。
安装node可以到 http://nodejs.cn/download/ 下载对应的 node 版本，之后双击安装即可。

git clone https://github.com/henszey/etcd-browser.git
cd etcd-browser/
vim server.js  

编辑server.js，修改内容如下：

var etcdHost = process.env.ETCD_HOST || '127.0.0.1';  # etcd 主机IP
var etcdPort = process.env.ETCD_PORT || 2379;          # etcd 主机端口
var serverPort = process.env.SERVER_PORT || 8000;      # etcd-browser 监听端口

然后启动

node server.js

访问：http://127.0.0.1:8000/

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