docker etcd

etcd是CoreOS團隊于2013年6月發起的開源項目，它的目標是構建一個高可用的分布式鍵值(key-value)數據庫，用于配置共享和服務發現

etcd內部采用raft協議作為一致性算法，etcd基于Go語言實現。

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etcd作為服務發現系統，有以下的特點：

• 簡單：安裝配置簡單，HTTP+JSON的 API進行交互，使用curl命令可以輕松使用
• 安全：支持SSL證書驗證機制
• 快速：根據官方提供的benchmark數據，單實例支持每秒1k+寫操作
• 可靠：采用raft算法，實現分布式系統數據的可用性和一致性
  • 分布式系統中數據分為控制數據和應用數據，etcd處理的數據為控制數據

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同一個分布式集群中的進程或服務，互相感知并建立鏈接，這就是服務發現。解決服務發現問題的三大支柱：

• 一個強一致性、高可用的服務存儲目錄
  • 基于Raft算法
• 一種注冊服務和監控服務健康狀態的機制
• 一種查找和鏈接服務的機制
• 微服務協同工作架構中，服務動態添加　

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etcd基本命令

集群搭建參考k8s集群搭建里的etcd

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更新一個節點

#首先查看所有節點
[root@slave2 ~]# etcdctl member list
646ec025a72fc8a: name=etcd3 peerURLs=http://192.168.132.133:2380 clientURLs=http://192.168.132.133:2379 isLeader=true
dde447f371b55f50: name=etcd1 peerURLs=http://192.168.132.131:2380 clientURLs=http://192.168.132.131:2379 isLeader=false
e96057c7f8ba5f4b: name=etcd2 peerURLs=http://192.168.132.132:2380 clientURLs=http://192.168.132.132:2379 isLeader=false#更新一個節點
[root@slave2 ~]# etcdctl member update 646ec025a72fc8a http://192.168.132.133:2380
Updated member with ID 646ec025a72fc8a in cluster

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刪除一個節點

#查看所有節點
[root@slave2 ~]# etcdctl member list
646ec025a72fc8a: name=etcd3 peerURLs=http://192.168.132.133:2380 clientURLs=http://192.168.132.133:2379 isLeader=false
dde447f371b55f50: name=etcd1 peerURLs=http://192.168.132.131:2380 clientURLs=http://192.168.132.131:2379 isLeader=true
e96057c7f8ba5f4b: name=etcd2 peerURLs=http://192.168.132.132:2380 clientURLs=http://192.168.132.132:2379 isLeader=false

#刪除一個節點
[root@slave2 ~]# etcdctl member remove 646ec025a72fc8a
Removed member 646ec025a72fc8a from cluster

#再次查看節點，使用當前命令報錯
[root@slave2 ~]# etcdctl member list
Error:  client: etcd cluster is unavailable or misconfigured; error #0: dial tcp 127.0.0.1:2379: getsockopt: connection refused
; error #1: dial tcp 127.0.0.1:4001: getsockopt: connection refused

error #0: dial tcp 127.0.0.1:2379: getsockopt: connection refused
error #1: dial tcp 127.0.0.1:4001: getsockopt: connection refused

#換一個命令
[root@slave2 ~]#  etcdctl --endpoints "http://192.168.132.131:2379" member list
dde447f371b55f50: name=etcd1 peerURLs=http://192.168.132.131:2380 clientURLs=http://192.168.132.131:2379 isLeader=true
e96057c7f8ba5f4b: name=etcd2 peerURLs=http://192.168.132.132:2380 clientURLs=http://192.168.132.132:2379 isLeader=false

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添加節點

#將刪除的節點添加回來
[root@slave2 ~]# etcdctl --endpoints "http://192.168.132.132:2379" member add etcd3 http://192.168.132.133:2380
Added member named etcd3 with ID 7a6809311b4a3579 to clusterETCD_NAME="etcd3"
ETCD_INITIAL_CLUSTER="etcd3=http://192.168.132.133:2380,etcd1=http://192.168.132.131:2380,etcd2=http://192.168.132.132:2380"
ETCD_INITIAL_CLUSTER_STATE="existing"
#再次查看，狀態為unstarted
[root@slave2 ~]# etcdctl --endpoints "http://192.168.132.132:2379" member list
7a6809311b4a3579[unstarted]: peerURLs=http://192.168.132.133:2380
dde447f371b55f50: name=etcd1 peerURLs=http://192.168.132.131:2380 clientURLs=http://192.168.132.131:2379 isLeader=true
e96057c7f8ba5f4b: name=etcd2 peerURLs=http://192.168.132.132:2380 clientURLs=http://192.168.132.132:2379 isLeader=false

清空目標節點數據

目標節點從集群中刪除后，成員信息會更新。新節點是作為一個全新的節點加入集群，如果data-dir有數據，etcd啟動時會讀取己經存在的數據，仍然用舊的memberID會造成無法加入集群，所以一定要清空新節點的data-dir。

#刪除的節點的主機
$ rm -rf /var/lib/etcd/etcd3

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在目標節點上啟動新增加的成員

修改配置文件中ETCD_INITIAL_CLUSTER_STATE標記為existing，如果為new，則會自動生成一個新的memberID，這和前面添加節點時生成的ID不一致，故日志中會報節點ID不匹配的錯。

[root@slave2 ~]# cat /etc/etcd/etcd.conf |grep -v "^#"
[Member]
ETCD_DATA_DIR="/var/lib/etcd/etcd3"
ETCD_LISTEN_PEER_URLS="http://192.168.132.133:2380"
ETCD_LISTEN_CLIENT_URLS="http://192.168.132.133:2379,http://127.0.0.1:2379"
ETCD_NAME="etcd3"
[Clustering]
ETCD_INITIAL_ADVERTISE_PEER_URLS="http://192.168.132.133:2380"
ETCD_ADVERTISE_CLIENT_URLS="http://192.168.132.133:2379"
ETCD_INITIAL_CLUSTER_STATE="existing"
ETCD_INITIAL_CLUSTER="etcd1=http://192.168.132.131:2380,etcd2=http://192.168.132.132:2380,etcd3=http://192.168.132.133:2380"

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重啟服務，再次查看

[root@slave2 ~]# systemctl restart etcd
[root@slave2 ~]# etcdctl --endpoints "http://192.168.132.132:2379" member list
7a6809311b4a3579: name=etcd3 peerURLs=http://192.168.132.133:2380 clientURLs=http://192.168.132.133:2379 isLeader=false
dde447f371b55f50: name=etcd1 peerURLs=http://192.168.132.131:2380 clientURLs=http://192.168.132.131:2379 isLeader=true
e96057c7f8ba5f4b: name=etcd2 peerURLs=http://192.168.132.132:2380 clientURLs=http://192.168.132.132:2379 isLeader=false
[root@slave2 ~]# etcdctl member list
7a6809311b4a3579: name=etcd3 peerURLs=http://192.168.132.133:2380 clientURLs=http://192.168.132.133:2379 isLeader=false
dde447f371b55f50: name=etcd1 peerURLs=http://192.168.132.131:2380 clientURLs=http://192.168.132.131:2379 isLeader=true
e96057c7f8ba5f4b: name=etcd2 peerURLs=http://192.168.132.132:2380 clientURLs=http://192.168.132.132:2379 isLeader=false

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