了解etcd

转载请注明出处,原文链接http://tailnode.tk/2017/01/%E...

说明

这是一篇非常入门的文章,让你大概了解一下etcd。写这篇文章时使用etcd的版本是3.1.0。
etcd是以实现共享配置和服务发现为目的,提供一致性的键值存储的分布式数据库。kubernetes等项目使用了etcd。

下载安装

这里下载release包,解压后是一些文档和两个二进制文件etcd和etcdctl。etcd是server端,etcdctl是客户端。将etcd和etcdctl加入PATH路径方便我们执行命令。

运行server

执行命令etcd,即可启动server

ming@ming:/tmp$ etcd
2017-02-14 14:04:40.164639 I | etcdmain: etcd Version: 3.1.0
2017-02-14 14:04:40.164725 I | etcdmain: Git SHA: 8ba2897
2017-02-14 14:04:40.164736 I | etcdmain: Go Version: go1.7.4
2017-02-14 14:04:40.164776 I | etcdmain: Go OS/Arch: linux/amd64
2017-02-14 14:04:40.164784 I | etcdmain: setting maximum number of CPUs to 4, total number of available CPUs is 4
2017-02-14 14:04:40.164850 W | etcdmain: no data-dir provided, using default data-dir ./default.etcd
2017-02-14 14:04:40.164934 I | etcdmain: advertising using detected default host "192.168.1.124"
2017-02-14 14:04:40.165855 I | embed: listening for peers on http://localhost:2380
2017-02-14 14:04:40.167090 I | embed: listening for client requests on localhost:2379
......

etcdctl

说明:etcd最新的API版本是v3。与v2相比,v3更高效更清晰。设置环境变量ETCDCTL_API=3。

ming@ming:/tmp$ export ETCDCTL_API=3
ming@ming:/tmp$ etcdctl version
etcdctl version: 3.1.0
API version: 3.1

键值对命令

put设置key,get取得key

ming@ming:/tmp$ etcdctl put msg "Hello TenxCloud"
OK
ming@ming:/tmp$ etcdctl get msg  
msg
Hello TenxCloud

del删除key

ming@ming:/tmp$ etcdctl get msg  
msg
Hello TenxCloud
ming@ming:/tmp$ etcdctl del msg
1
ming@ming:/tmp$ etcdctl get msg
ming@ming:/tmp$ 

txn事务
txn从标准输入中读取多个请求,将它们看做一个原子性的事务执行。事务是由条件列表,条件判断成功时的执行列表(条件列表中全部条件为真表示成功)和条件判断失败时的执行列表(条件列表中有一个为假即为失败)组成的。
看文字解释容易晕,来看实例吧

ming@ming:/tmp$ etcdctl put flag 1
OK
ming@ming:/tmp$ etcdctl txn -i
compares:
value("flag") = "1"
success requests (get, put, delete):
put result true
failure requests (get, put, delete):
put result false
SUCCESS
OK
ming@ming:/tmp$ etcdctl get result
result
true

解释一下:

  1. etcdctl put flag 1设置flag为1

  2. etcdctl txn -i开启事务(-i表示交互模式)

  3. 第2步输入命令后回车,终端显示出compares:

  4. 输入value("flag") = "1",此命令是比较flag的值与1是否相等

  5. 第4步完成后输入回车,终端会换行显示,此时可以继续输入判断条件(前面说过事务由条件列表组成),再次输入回车表示判断条件输入完毕

  6. 第5步连续输入两个回车后,终端显示出success requests (get, put, delete):,表示下面输入判断条件为真时要执行的命令

  7. 与输入判断条件相同,连续两个回车表示成功时的执行列表输入完成

  8. 终端显示failure requests (get, put, delete):后输入条件判断失败时的执行列表

  9. 为了看起来简洁,此实例中条件列表和执行列表只写了一行命令,实际可以输入多行

  10. 总结上面的事务,要做的事情就是flag为1时设置result为true,否则设置result为false

  11. 事务执行完成后查看result值为true

watch监听
watch后etcdctl阻塞,在另一个终端中执行etcdctl put flag 2后,watch会打印出相关信息

ming@ming:/tmp$ etcdctl watch flag
PUT
flag
2

lease租约
etcd也能为key设置超时时间,但与redis不同,etcd需要先创建lease,然后使用put命令加上参数–lease=<lease ID>来设置

ming@ming:/tmp$ etcdctl lease grant 100
lease 38015a3c00490513 granted with TTL(100s)
ming@ming:/tmp$ etcdctl put k1 v1 --lease=38015a3c00490513
OK
ming@ming:/tmp$ etcdctl lease timetolive 38015a3c00490513
lease 38015a3c00490513 granted with TTL(100s), remaining(67s)
ming@ming:/tmp$ etcdctl lease timetolive 38015a3c00490513
lease 38015a3c00490513 granted with TTL(100s), remaining(64s)
ming@ming:/tmp$ etcdctl lease timetolive 38015a3c00490513 --keys
lease 38015a3c00490513 granted with TTL(100s), remaining(59s), attached keys([k1])
ming@ming:/tmp$ etcdctl put k2 v2 --lease=38015a3c00490513
OK
ming@ming:/tmp$ etcdctl lease timetolive 38015a3c00490513 --keys
lease 38015a3c00490513 granted with TTL(100s), remaining(46s), attached keys([k1 k2])
ming@ming:/tmp$ etcdctl lease revoke 38015a3c00490513 
lease 38015a3c00490513 revoked
ming@ming:/tmp$ etcdctl get k1
ming@ming:/tmp$ etcdctl get k2
ming@ming:/tmp$ 
ming@ming:/tmp$ etcdctl lease grant 10
lease 38015a3c0049051d granted with TTL(10s)
ming@ming:/tmp$ etcdctl lease keep-alive 38015a3c0049051d
lease 38015a3c0049051d keepalived with TTL(10)
lease 38015a3c0049051d keepalived with TTL(10)
lease 38015a3c0049051d keepalived with TTL(10)

lease grant <ttl>
创建lease,返回lease ID。创建的lease生存时间大于或等于ttl秒(TODO:为什么可能大于?)
lease revoke <lease ID>
删除lease,并删除所有关联的key
lease timetolive <lease ID>
取得lease的总时间和剩余时间
lease keep-alive <lease ID>
此命令不会只更新一次lease时间,而是周期性地刷新,保证它不会过期。

集群管理命令

TODO

并发控制命令

lock <lock name>
通过指定的名字加锁。注意,只有当正常退出且释放锁后,lock命令的退出码是0,否则这个锁会一直被占用直到过期(默认60秒)

使用Ctrl+C正常退出lock命令,退出码为0,第二次能正常lock:
ming@ming:/tmp$ etcdctl lock test
test/38015a3fd6795e04
^Cming@ming:/tmp$ echo $?
0
ming@ming:/tmp$ etcdctl lock test
test/38015a3fd6795e0a

kill掉lock命令,退出码不为0,第二次lock被阻塞:
终端1,第一次正常锁住test:
ming@ming:/tmp$ etcdctl lock test
test/38015a3fd6795e11


终端2,kill掉lock命令:
ming@ming:~$ ps aux|grep 'etcdctl lock'
ming      44546  0.5  0.5  19876 11436 pts/5    Sl+  11:42   0:00 etcdctl lock test
ming      44560  0.0  0.0  14224  1084 pts/6    S+   11:43   0:00 grep --color=auto etcdctl lock
ming@ming:~$ kill -9 44546
 
终端1,退出码不为0,第二次锁test被阻塞
ming@ming:/tmp$ etcdctl lock test
test/38015a3fd6795e1e
Killed
ming@ming:/tmp$ echo $?
137
ming@ming:/tmp$ etcdctl lock test

elect
TODO

权限命令

user
可以为etcd创建多个用户并设置密码,子命令有:

  • add 添加用户

  • delete 删除用户

  • get 取得用户详情

  • list 列出所有用户

  • passwd 修改用户密码

  • grant-role 给用户分配角色

  • revoke-role 给用户移除角色

role
可以为etcd创建多个角色并设置权限,子命令有:

  • add 添加角色

  • delete 删除角色

  • get 取得角色信息

  • list 列出所有角色

  • grant-permission 为角色设置某个key的权限

  • revoke-permission 为角色移除某个key的权限

auth
开启/关闭权限控制

示例
下面以示例来学习这三个命令

root用户存在时才能开启权限控制
ming@ming:/tmp$ etcdctl auth enable
Error:  etcdserver: root user does not exist
ming@ming:/tmp$ etcdctl user add root
Password of root: 
Type password of root again for confirmation: 
User root created
ming@ming:/tmp$ etcdctl auth enable
Authentication Enabled
 
开启权限控制后需要用--user指定用户
ming@ming:/tmp$ etcdctl user list
Error:  etcdserver: user name not found
ming@ming:/tmp$ etcdctl user list --user=root
Password: 
root
ming@ming:/tmp$ etcdctl user get root --user=root
Password: 
User: root
Roles: root
 
添加用户,前两个密码是新用户的,后一个密码是root的
ming@ming:/tmp$ etcdctl user add mengyuan --user=root
Password of mengyuan: 
Type password of mengyuan again for confirmation: 
Password: 
User mengyuan created
 
使用新用户执行put命令,提示没有权限
ming@ming:/tmp$ etcdctl put key1 v1 --user=mengyuan
Password: 
Error:  etcdserver: permission denied
创建名为rw_key_的role,添加对字符串"key"做为前缀的key的读写权限,为mengyuan添加角色
ming@ming:/tmp$ etcdctl role add rw_key_ --user=root
Password: 
Role rw_key_ created
ming@ming:/tmp$ etcdctl --user=root role grant-permission rw_key_ readwrite key --prefix=true
Password: 
Role rw_key_ updated
ming@ming:/tmp$ etcdctl --user=root user grant-role mengyuan rw_key_
Password: 
Role rw_key_ is granted to user mengyuan
 
添加权限成功后执行put key1成功,执行put k1失败(因为上面只给前缀为"key"的key添加了权限)
ming@ming:/tmp$ etcdctl put key1 v1 --user=mengyuan
Password: 
OK
ming@ming:/tmp$ etcdctl put k1 v1 --user=mengyuan
Password: 
Error:  etcdserver: permission denied
 
执行user list命令失败,没有权限
ming@ming:/tmp$ etcdctl user list --user=mengyuan
Password: 
Error:  etcdserver: permission denied
为新用户添加root的角色后就能执行user list命令了,注意命令中第一个root是角色,第二个root是用户
ming@ming:/tmp$ etcdctl user grant-role mengyuan root --user=root
Password: 
Role root is granted to user mengyuan
ming@ming:/tmp$ etcdctl user list --user=mengyuan
Password: 
mengyuan
root

进一步学习

  • etcdctl <command> -h查看子命令的帮助(例:etcdctl watch -h)

  • http://play.etcd.io/play 是网页版集群环境

  • etcdctl能够设置--prefix=true来操作多个指定前缀的key

参考文档

https://github.com/coreos/etcd
https://github.com/coreos/etc...


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