简介

etcd是一个开源的用于配置共享和服务发现的高性能的键值存储系统，由CoreOS团队开发，也是CoreOS的核心组件，负责CoreOS的自动安全更新、容器相关的覆盖网络设置等功能。

利用 etcd 的特性，应用程序可以在集群中共享信息、配置或作服务发现，etcd 会在集群的各个节点中复制这些数据并保证这些数据始终正确。

etcd 无论是在 CoreOS 还是 Kubernetes 体系中都是不可或缺的一环。

本文介绍etcd的安装和集群搭建，供初次使用者上手。

安装和基本用法

etcd代码在github上维护，Github地址 直接在relase页面找到想安装的版本的二进制包，下载地址

安装和启动etcd

curl -L  https://github.com/coreos/etcd/releases/download/v2.2.2/etcd-v2.2.2-linux-amd64.tar.gz -o etcd-v2.2.2-linux-amd64.tar.gz
tar xzvf etcd-v2.2.2-linux-amd64.tar.gz
cd etcd-v2.2.2-linux-amd64
# 使用默认配置启动etcd
./etcd
# 可以看到启动log，服务监听了如下4个端口
2015-12-24 07:34:49.094992 I | etcdmain: listening for peers on http://localhost:2380
2015-12-24 07:34:49.095038 I | etcdmain: listening for peers on http://localhost:7001
2015-12-24 07:34:49.095078 I | etcdmain: listening for client requests on http://localhost:2379
2015-12-24 07:34:49.095116 I | etcdmain: listening for client requests on http://localhost:4001

使用etcdctl来测试etcd

./etcdctl set test_key "the value is for testing."
./etcdctl get test_key 

也可以使用curl直接发送http请求，来测试etcd的接口

curl -L http://127.0.0.1:4001/version
{"etcdserver":"2.2.2","etcdcluster":"2.2.0"}

curl -L http://127.0.0.1:4001/v2/keys/test_key -XPUT -d value="changed by curl"
{"action":"set","node":{"key":"/test_key","value":"changed by curl","modifiedIndex":5,"createdIndex":5},"prevNode":{"key":"/test_key","value":"the value is for testing.","modifiedIndex":4,"createdIndex":4}}

curl -L http://127.0.0.1:4001/v2/keys/test_key
{"action":"get","node":{"key":"/test_key","value":"changed by curl","modifiedIndex":5,"createdIndex":5}}

搭建etcd集群

首先，找三台服务器，可以购买云主机，或本地启动虚拟机。 ip如下，注意iptables等防火墙设置，测试网络互通。 infra0 192.168.1.116 infra1 192.168.1.118 infra2 192.168.1.117

Static方式搭建etcd集群

在192.168.1.116这台机器上

./etcd -name infra0 -initial-advertise-peer-urls http://192.168.1.116:2380 \
  -listen-peer-urls http://192.168.1.116:2380 \
  -listen-client-urls http://192.168.1.116:2379,http://127.0.0.1:2379 \
  -advertise-client-urls http://192.168.1.116:2379 \
  -initial-cluster-token etcd-cluster-1 \
  -initial-cluster infra0=http://192.168.1.116:2380,infra1=http://192.168.1.118:2380,infra2=http://192.168.1.117:2380 \
  -initial-cluster-state new
# log
etcdserver: published {Name:infra0 ClientURLs:[http://192.168.1.116:2379]} to cluster f075b34d7da81569

在192.168.1.118这台机器上

./etcd -name infra1 -initial-advertise-peer-urls http://192.168.1.118:2380 \
  -listen-peer-urls http://192.168.1.118:2380 \
  -listen-client-urls http://192.168.1.118:2379,http://127.0.0.1:2379 \
  -advertise-client-urls http://192.168.1.118:2379 \
  -initial-cluster-token etcd-cluster-1 \
  -initial-cluster infra0=http://192.168.1.116:2380,infra1=http://192.168.1.118:2380,infra2=http://192.168.1.117:2380 \
  -initial-cluster-state new
# log
etcdserver: published {Name:infra1 ClientURLs:[http://192.168.1.118:2379]} to cluster f075b34d7da81569

在192.168.1.117这台机器上

./etcd -name infra2 -initial-advertise-peer-urls http://192.168.1.117:2380 \
  -listen-peer-urls http://192.168.1.117:2380 \
  -listen-client-urls http://192.168.1.117:2379,http://127.0.0.1:2379 \
  -advertise-client-urls http://192.168.1.117:2379 \
  -initial-cluster-token etcd-cluster-1 \
  -initial-cluster infra0=http://192.168.1.116:2380,infra1=http://192.168.1.118:2380,infra2=http://192.168.1.117:2380 \
  -initial-cluster-state new
# log
etcdserver: published {Name:infra2 ClientURLs:[http://192.168.1.117:2379]} to cluster f075b34d7da81569

测试：

# 在192.168.1.116节点写入key
curl -L http://192.168.1.116:2379/v2/keys/cluster_test -XPUT -d value="for cluster"
{"action":"set","node":{"key":"/cluster_test","value":"for cluster","modifiedIndex":9,"createdIndex":9}}

# 在其他节点读到key
curl -L http://192.168.1.118:2379/v2/keys/cluster_test
{"action":"get","node":{"key":"/cluster_test","value":"for cluster","modifiedIndex":9,"createdIndex":9}}

总结

本文讲述了etcd的安装方法和基本使用，还包括etcd集群搭建方法等，让读者简明的了解etcd这个软件的基本用法。