介绍
etcd 是一个分布式、可靠的键值存储数据库，用于收集分布式系统中最关键的数据。是k8s的组件之一，使用Raft一致性算法，为分布式系统而生。常用做服务发现和配置共享等应用场景。
可以使用protobuf定义的接口来进行开发，这里使用更易测试验证的第三方python库etcd3举例。
这里需要注意的一点是：“ raft算法写入时需要半数以上的节点写入成功才返回，宕机节点不超过半数则数据不丢失。” 即： 3个节点的集群，1个节点宕机无妨。但两个节点宕机后，即使另一个节点存活也无法读取数据！。四个节点集群也是两个节点宕机后，无法工作。5个节点则允许两个节点宕机。满足公式quorum=(n+1)/2。所以建议奇数的集群节点。因为奇数和偶数的可靠性一样，单可以节省1个节点的资源。
下载与安装
etcd 下载
etcd v3.4 文档
简单测试
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# 运行
./etcd
# etcd put 命令用于设置给定 key 的值。如果 key 已经存储其他值， put 就覆写旧值.
./etcdctl put greeting "Hello, etcd"
# 通过key获取value
./etcdctl get greeting
# 删除 kv
./etcdctl del greeting
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使用docker-compose组建4节点集群。
docker-compose.yaml
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version: '2'
networks:
byfn:
services:
etcd1:
image: quay.io/coreos/etcd
container_name: etcd1
command: etcd -name etcd1 -advertise-client-urls http://0.0.0.0:2379 -listen-client-urls http://0.0.0.0:2379 -listen-peer-urls http://0.0.0.0:2380 -initial-cluster-token etcd-cluster -initial-cluster "etcd1=http://etcd1:2380,etcd2=http://etcd2:2380,etcd3=http://etcd3:2380,etcd4=http://etcd4:2380" -initial-cluster-state new
ports:
- 2385:2379
- 2380
networks:
- byfn
etcd2:
image: quay.io/coreos/etcd
container_name: etcd2
command: etcd -name etcd2 -advertise-client-urls http://0.0.0.0:2379 -listen-client-urls http://0.0.0.0:2379 -listen-peer-urls http://0.0.0.0:2380 -initial-cluster-token etcd-cluster -initial-cluster "etcd1=http://etcd1:2380,etcd2=http://etcd2:2380,etcd3=http://etcd3:2380,etcd4=http://etcd4:2380" -initial-cluster-state new
ports:
- 2386:2379
- 2380
networks:
- byfn
etcd3:
image: quay.io/coreos/etcd
container_name: etcd3
command: etcd -name etcd3 -advertise-client-urls http://0.0.0.0:2379 -listen-client-urls http://0.0.0.0:2379 -listen-peer-urls http://0.0.0.0:2380 -initial-cluster-token etcd-cluster -initial-cluster "etcd1=http://etcd1:2380,etcd2=http://etcd2:2380,etcd3=http://etcd3:2380,etcd4=http://etcd4:2380" -initial-cluster-state new
ports:
- 2387:2379
- 2380
networks:
- byfn
etcd4:
image: quay.io/coreos/etcd
container_name: etcd4
command: etcd -name etcd4 -advertise-client-urls http://0.0.0.0:2379 -listen-client-urls http://0.0.0.0:2379 -listen-peer-urls http://0.0.0.0:2380 -initial-cluster-token etcd-cluster -initial-cluster "etcd1=http://etcd1:2380,etcd2=http://etcd2:2380,etcd3=http://etcd3:2380,etcd4=http://etcd4:2380" -initial-cluster-state new
ports:
- 2388:2379
- 2380
networks:
- byfn
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运行 docker-compose up 即可
使用虚拟机组建4节点集群。
4个虚拟机分别运行以下命令：
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# 虚拟机1 192.168.0.156
./etcd --name infra0 --initial-advertise-peer-urls http://192.168.0.156:2380 \
--listen-peer-urls http://192.168.0.156:2380 \
--listen-client-urls http://192.168.0.156:2379,http://127.0.0.1:2379 \
--advertise-client-urls http://192.168.0.156:2379 \
--initial-cluster-token etcd-cluster-1 \
--initial-cluster infra0=http://192.168.0.156:2380,infra1=http://192.168.0.157:2380,infra2=http://192.168.0.158:2380,infra3=http://192.168.0.159:2380 \
--initial-cluster-state new
# 虚拟机2 192.168.0.157
./etcd --name infra1 --initial-advertise-peer-urls http://192.168.0.157:2380 \
--listen-peer-urls http://192.168.0.157:2380 \
--listen-client-urls http://192.168.0.157:2379,http://127.0.0.1:2379 \
--advertise-client-urls http://192.168.0.157:2379 \
--initial-cluster-token etcd-cluster-1 \
--initial-cluster infra0=http://192.168.0.156:2380,infra1=http://192.168.0.157:2380,infra2=http://192.168.0.158:2380,infra3=http://192.168.0.159:2380 \
--initial-cluster-state new
# 虚拟机3 192.168.0.158
etcd --name infra2 --initial-advertise-peer-urls http://192.168.0.158:2380 \
--listen-peer-urls http://192.168.0.158:2380 \
--listen-client-urls http://192.168.0.158:2379,http://127.0.0.1:2379 \
--advertise-client-urls http://192.168.0.158:2379 \
--initial-cluster-token etcd-cluster-1 \
--initial-cluster infra0=http://192.168.0.156:2380,infra1=http://192.168.0.157:2380,infra2=http://192.168.0.158:2380,infra3=http://192.168.0.159:2380 \
--initial-cluster-state new
# 虚拟机4 192.168.0.159
etcd --name infra3 --initial-advertise-peer-urls http://192.168.0.159:2380 \
--listen-peer-urls http://192.168.0.159:2380 \
--listen-client-urls http://192.168.0.159:2379,http://127.0.0.1:2379 \
--advertise-client-urls http://192.168.0.159:2379 \
--initial-cluster-token etcd-cluster-1 \
--initial-cluster infra0=http://192.168.0.156:2380,infra1=http://192.168.0.157:2380,infra2=http://192.168.0.158:2380,infra3=http://192.168.0.159:2380 \
--initial-cluster-state new
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python etcd3 库测试
安装 pip3 install etcd3
etcd3文档
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import etcd3
# 建立连接
etcd = etcd3.client(host='127.0.0.1', port=2379)
# 添加 kv
result = etcd.put('greeting', 'hello, world!')
"""
header {
cluster_id: 14841639068965178418
member_id: 10276657743932975437
revision: 16
raft_term: 5
}
"""
# 根据 key 获得 value
result = etcd.get('greeting') # 不存在 (None, None); 存在(b'hello, world!', <etcd3.client.KVMetadata object at 0x7ffbf072de80>)
rv = result[0].decode() if result[0] else result[0] # 取解析后的值
# 删除某个 key
result = etcd.delete('greeting') # 成功删除 True， 不存在，删除失败 False
# 返回满足前缀 key 的 value
objs = etcd.get_prefix("server1")
result = [obj[0].decode() if obj[0] else obj[0] for obj in objs]
# 获取所有的 key的 value
objs = etcd.get_all()
result = [obj[0].decode() if obj[0] else obj[0] for obj in objs]
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