MongoDB副本集强制其中一个节点为主库并重做副本集集群案例分享
配置环境：
CentOS:
[root@node252 lib]# uname -a
Linux node252 3.10.0-957.el7.x86_64 #1 SMP Thu Nov 8 23:39:32 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
[root@node252 lib]# cat /etc/redhat-release
CentOS Linux release 7.6.1810 (Core)
[root@node252 lib]# rpm -qa | grep mongo
mongodb-org-mongos-4.0.18-1.el7.x86_64
mongodb-org-server-4.0.18-1.el7.x86_64
mongodb-org-shell-4.0.18-1.el7.x86_64
mongodb-org-tools-4.0.18-1.el7.x86_64
mongodb-org-4.0.18-1.el7.x86_64
在mongodb副本集集群中,若是丢失了n/2+1个节点,也就是失去了多数节点时候,在集群内无法投票表决剩下的节点谁能当主库,那就需要强制其中一个节点为主库.
下面是操作步骤:
1.执行cfg=rs.conf()
2.需要设置需要的_id为主库，
cfg.members=[cfg.members[3]]
3.执行集群重新设置
4.rs.reconfig(cfg, {force: true});
5.rs.status()
下面是详细操作步骤,
该集群是四个节点的副本集,其中三个节点已经丢失,使剩下的节点为主节点,单实例运行，最后一个节点的状态将变成SECONDARY,上层应用将会法插入数，但可以读取数据。
执行cfg=rs.conf(),获取集群的节点信息:
cms:SECONDARY> cfg=rs.conf()
{
"_id" : "cms",
"version" : 32948,
"protocolVersion" : NumberLong(1),
"members" : [
{
"_id" : 0,
"host" : "192.168.1.193:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
},
{
"_id" : 1,
"host" : "192.168.1.195:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
},
{
"_id" : 2,
"host" : "192.168.1.198:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
},
{
"_id" : 3,
"host" : "192.168.1.199:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
}
],
"settings" : {
"chainingAllowed" : true,
"heartbeatIntervalMillis" : 2000,
"heartbeatTimeoutSecs" : 10,
"electionTimeoutMillis" : 10000,
"getLastErrorModes" : {
},
"getLastErrorDefaults" : {
"w" : 1,
"wtimeout" : 0
},
"replicaSetId" : ObjectId("59cab0d69b86b9e815cfc02b")
}
}
下面指定199为主节点
cms:SECONDARY> cfg.members=[cfg.members[3]]
[
{
"_id" : 3,
"host" : "192.168.1.199:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
}
]
应用配置：
cms:SECONDARY> rs.reconfig(cfg, {force: true})
{ "ok" : 1 }
}
cms:PRIMARY> #这样应用就可以正常访问单主集群了
将单主集群重建副本集集群：
查看更改后的集群状态,操作完成,变成了单实例节点.然后通过添加从节点来实现副本集
cms:SECONDARY> rs.status()
{
"set" : "cms",
"date" : ISODate("2018-09-04T01:54:12.445Z"),
"myState" : 1,
"term" : NumberLong(6),
"heartbeatIntervalMillis" : NumberLong(2000),
"members" : [
{
"_id" : 3,
"name" : "192.168.1.199:27017",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 3152420,
"optime" : {
"ts" : Timestamp(1536026052, 24),
"t" : NumberLong(6)
},
"optimeDate" : ISODate("2018-09-04T01:54:12Z"),
"infoMessage" : "could not find member to sync from",
"electionTime" : Timestamp(1536026047, 1),
"electionDate" : ISODate("2018-09-04T01:54:07Z"),
"configVersion" : 137682,
"self" : true
}
],
"ok" : 1
}
如果从节点在运行，要强制停止从节点的服务：
在启动mongod进程前,必须要把新节点数据文件清空.
注意：如果有配置KEY认证，不能删除相应的文件夹：
#security:
security:
clusterAuthMode: keyFile
keyFile: /var/lib/mongo/key/repl_set.key
authorization: enabled
#operationProfiling:
清空SECONDARY节点的数据,(除key文件夹外)：
[root@node251 ~]# cd /var/lib/mongo/
[root@node251 mongo]# ls
collection-0-1410376559665338345.wt diagnostic.data index-7-1410376559665338345.wt
collection-0-2428134951873617012.wt index-11-1410376559665338345.wt index-9-1410376559665338345.wt
collection-0--340382256029554464.wt index-1-1410376559665338345.wt journal
collection-10-1410376559665338345.wt index-1-2428134951873617012.wt key
collection-16-1410376559665338345.wt index-1--340382256029554464.wt _mdb_catalog.wt
collection-17-1410376559665338345.wt index-18-1410376559665338345.wt mongod.lock
collection-19-1410376559665338345.wt index-20-1410376559665338345.wt sizeStorer.wt
collection-21-1410376559665338345.wt index-22-1410376559665338345.wt storage.bson
collection-2-1410376559665338345.wt index-2-2428134951873617012.wt WiredTiger
collection-23-1410376559665338345.wt index-24-1410376559665338345.wt WiredTigerLAS.wt
collection-4-1410376559665338345.wt index-25-1410376559665338345.wt WiredTiger.lock
collection-6-1410376559665338345.wt index-3-1410376559665338345.wt WiredTiger.turtle
collection-8-1410376559665338345.wt index-5-1410376559665338345.wt WiredTiger.wt
[root@node251 mongo]# rm -rf ./*.wt
[root@node251 mongo]# ls
diagnostic.data journal key mongod.lock storage.bson WiredTiger WiredTiger.lock WiredTiger.turtle
[root@node251 mongo]# rm -rf mongod.lock storage.bson WiredTiger WiredTiger.lock WiredTiger.turtle
[root@node251 mongo]# rm -rf diagnostic.data journal
[root@node251 mongo]# ls
key
启动本地的mongodb进程：
systemctl start mongod
在主节点添加新的节点,指定priority,这个值一定要比主节点的priority低:
查看primary节点的priority值：
rs0:PRIMARY> rs.config();
{
"_id" : "cms",
"version" : 155928,
"protocolVersion" : NumberLong(1),
"writeConcernMajorityJournalDefault" : true,
"members" : [
{
"_id" : 0,
"host" : "192.168.1.199:27017",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 10,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
}
],
"settings" : {
"chainingAllowed" : true,
"heartbeatIntervalMillis" : 2000,
"heartbeatTimeoutSecs" : 10,
"electionTimeoutMillis" : 10000,
"catchUpTimeoutMillis" : -1,
"catchUpTakeoverDelayMillis" : 30000,
"getLastErrorModes" : {
},
"getLastErrorDefaults" : {
"w" : 1,
"wtimeout" : 0
},
"replicaSetId" : ObjectId("5ea6ea6c7b4b6caf94cb5ab3")
}
}
修改集群配置：
config = { _id:"cms", "protocolVersion" : 1,members:
[
{_id:0,host:"192.168.1.193:27017",priority:1},
{_id:1,host:"192.168.1.194:27017",priority:2},
{_id:2,host:"192.168.1.198:27017",priority:3},
{_id:3,host:"192.168.1.199:27017",priority:4}
]
}
======一主一从一仲裁节点========
config = { _id : "rs0", "protocolVersion" : 1,members : [ {_id : 0, host : "172.16.1.250:27017","priority":3 }, {_id : 1, host : "172.16.1.251:27017","priority":1}, {_id : 2, host : "172.16.1.252:27017","arbiterOnly":true} ] };
# 重新配置副本集
rs.reconfig(config);
==============
rs.reconfig(config);
配置完成后，SECONDARY会自动拉取主库数据,然后创建索引.
