ETCD 简介及基本用法

ETCD 项目地址

ETCD 官方文档

1. 简介

ETCD 是一个高可用的分布式键值数据库，可用于服务发现。ETCD 采用 raft 一致性算法，基于 Go 语言实现。

特点

简单：安装配置使用简单，提供 HTTP API

安全：支持 SSL 证书

可靠：采用 raft 算法，实现分布式系统数据的可用性和一致性

2. 用法

通过 etcdctl 可以使用 ETCD。假设使用 v3 版本，且集群设置如下：

export ETCDCTL_API=3
HOST_1=10.240.0.17
HOST_2=10.240.0.18
HOST_3=10.240.0.19
ENDPOINTS=$HOST_1:2379,$HOST_2:2379,$HOST_3:2379

etcdctl --endpoints=$ENDPOINTS member list

版本设置

ETCD v2 和 v3 两个版本不兼容，且 v2 已经停止支持。如果一个系统上同时按照了两个版本，需要通过环境变量来切换：

export ETCDCTL_API=3

读写数据

put 命令写数据：

etcdctl --endpoints=$ENDPOINTS put foo "Hello World!"

get 命令读数据：

etcdctl --endpoints=$ENDPOINTS get foo
etcdctl --endpoints=$ENDPOINTS --write-out="json" get foo

通过 --write-out="json" 选项读数据时，会读包括元数据在内的所有数据，并以 JSON 格式输出。

通过 prefix 选项读数据

etcdctl --endpoints=$ENDPOINTS put web1 value1
etcdctl --endpoints=$ENDPOINTS put web2 value2
etcdctl --endpoints=$ENDPOINTS put web3 value3

etcdctl --endpoints=$ENDPOINTS get web --prefix

删除数据

etcdctl --endpoints=$ENDPOINTS put key myvalue
etcdctl --endpoints=$ENDPOINTS del key

etcdctl --endpoints=$ENDPOINTS put k1 value1
etcdctl --endpoints=$ENDPOINTS put k2 value2
etcdctl --endpoints=$ENDPOINTS del k --prefix

事务性写入 txn

通过 txn 可以将多个请求放入一个事务：

etcdctl --endpoints=$ENDPOINTS put user1 bad
etcdctl --endpoints=$ENDPOINTS txn --interactive

compares:
value("user1") = "bad"      

success requests (get, put, delete):
del user1  

failure requests (get, put, delete):
put user1 good

监控数据变化 watch

通过 watch 选项，可以在将来发生改变时获得通知：

etcdctl --endpoints=$ENDPOINTS watch stock1
etcdctl --endpoints=$ENDPOINTS put stock1 1000

etcdctl --endpoints=$ENDPOINTS watch stock --prefix
etcdctl --endpoints=$ENDPOINTS put stock1 10
etcdctl --endpoints=$ENDPOINTS put stock2 20

安全写入 lease

lease 选项可以通过 TTL 写入数据：

etcdctl --endpoints=$ENDPOINTS lease grant 300
# lease 2be7547fbc6a5afa granted with TTL(300s)

etcdctl --endpoints=$ENDPOINTS put sample value --lease=2be7547fbc6a5afa
etcdctl --endpoints=$ENDPOINTS get sample

etcdctl --endpoints=$ENDPOINTS lease keep-alive 2be7547fbc6a5afa
etcdctl --endpoints=$ENDPOINTS lease revoke 2be7547fbc6a5afa
# or after 300 seconds
etcdctl --endpoints=$ENDPOINTS get sample

分布式锁 lock

etcdctl --endpoints=$ENDPOINTS lock mutex1

# another client with the same name blocks
etcdctl --endpoints=$ENDPOINTS lock mutex1

集群状态

为每台机器指定初始群集配置：

etcdctl --write-out=table --endpoints=$ENDPOINTS endpoint status

+------------------+------------------+---------+---------+-----------+-----------+------------+
|     ENDPOINT     |        ID        | VERSION | DB SIZE | IS LEADER | RAFT TERM | RAFT INDEX |
+------------------+------------------+---------+---------+-----------+-----------+------------+
| 10.240.0.17:2379 | 4917a7ab173fabe7 | 3.0.0   | 45 kB   | true      |         4 |      16726 |
| 10.240.0.18:2379 | 59796ba9cd1bcd72 | 3.0.0   | 45 kB   | false     |         4 |      16726 |
| 10.240.0.19:2379 | 94df724b66343e6c | 3.0.0   | 45 kB   | false     |         4 |      16726 |
+------------------+------------------+---------+---------+-----------+-----------+------------+

etcdctl --endpoints=$ENDPOINTS endpoint health

10.240.0.17:2379 is healthy: successfully committed proposal: took = 3.345431ms
10.240.0.19:2379 is healthy: successfully committed proposal: took = 3.767967ms
10.240.0.18:2379 is healthy: successfully committed proposal: took = 4.025451ms

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