MongoDB 復(fù)制集的選舉原理

復(fù)制的原理

        復(fù)制時(shí)基于啊哦做日志 oplog , 相當(dāng)于 MySQL 中的二進(jìn)制日志，只記錄發(fā)生改變的記錄。復(fù)制是將主節(jié)點(diǎn)的oplog 日志同步并應(yīng)用到其他從節(jié)點(diǎn)的過(guò)程。

選舉的原理

      節(jié)點(diǎn)類(lèi)型分為標(biāo)準(zhǔn)（host）節(jié)點(diǎn) 、被動(dòng)（passive）節(jié)點(diǎn)和仲裁（arbiter）節(jié)點(diǎn)。

（1）只有標(biāo)準(zhǔn)節(jié)點(diǎn)可能被選舉為活躍（primary）節(jié)點(diǎn)，有選舉權(quán)。被動(dòng)節(jié)點(diǎn)有完整副本，不可能成為活躍節(jié)點(diǎn)，有選舉權(quán)。仲裁節(jié)點(diǎn)不復(fù)制數(shù)據(jù)，不可能成為活躍節(jié)點(diǎn)，只有選舉權(quán)。

（2）標(biāo)準(zhǔn)節(jié)點(diǎn)與被動(dòng)節(jié)點(diǎn)的區(qū)別：primary 值高者是標(biāo)準(zhǔn)節(jié)點(diǎn)，低者則為被動(dòng)節(jié)點(diǎn)。

（3）選舉規(guī)則是票數(shù)高者獲勝，primary 是優(yōu)先權(quán)為 0~1000 的值，相當(dāng)于額為增加 0~1000 的票數(shù)。選舉結(jié)果：票數(shù)高者獲勝；若票數(shù)相同，數(shù)據(jù)新者獲勝。

實(shí)驗(yàn)部署

搭建配置4個(gè) MongoDB 實(shí)例 mongodb  、mongpdb2 、mongodb3 、mongodb4 。 IP 地址：192.168.213.184

由于MongoDB 數(shù)據(jù)庫(kù)安裝好后，mongodb 為默認(rèn)第一個(gè)實(shí)例，因此只要再搭建2 ,3，4 實(shí)例即可

1. 配置復(fù)制集

（1）創(chuàng)建數(shù)據(jù)文件和日志文件存儲(chǔ)路徑

[root@localhost ~]# mkdir -p /data/mongodb/mongodb{2,3,4}                #創(chuàng)建數(shù)據(jù)庫(kù)文件2,3,4
[root@localhost ~]# cd /data/mongodb/
[root@localhost mongodb]# ls
mongodb2  mongodb3  mongodb4
[root@localhost mongodb]# mkdir logs
[root@localhost mongodb]# ls
logs  mongodb2  mongodb3  mongodb4
[root@localhost mongodb]# cd logs/
[root@localhost logs]# touch mongodb{2,3,4}.log                            #在 /data/mongodb/logs/ 目錄下的日志存儲(chǔ)路徑
[root@localhost logs]# chmod  - R 777 /data/mongodb/logs/*.log         #修改目錄權(quán)限   
[root@localhost logs]# ls -l
總用量 0
-rwxrwxrwx. 1 root root 0 9月  13 18:43 mongodb2.log
-rwxrwxrwx. 1 root root 0 9月  13 18:43 mongodb3.log
-rwxrwxrwx. 1 root root 0 9月  13 18:43 mongodb4.log

（2）配置實(shí)例1 的配置文件，啟用復(fù)制集名稱(chēng)

[root@localhost logs]# vim /etc/mongod.conf
replication:
      replSetName: abc                        #去掉注釋?zhuān)付◤?fù)制集名稱(chēng)（名稱(chēng)隨便定義）

創(chuàng)建多實(shí)例配置文件

[root@localhost logs]# cp -p /etc/mongod.conf /etc/mongod2.conf        復(fù)制生成實(shí)例2 的配置文件
[root@localhost logs]# vim /etc/mongod2.conf

systemLog:
   destination: file
   logAppend: true
   path: /data/mongodb/logs/mongodb2.log             #日志文件位置    

storage:
   dbPath: /data/mongodb/mongodb2                        #數(shù)據(jù)文件位置
   journal:
     enabled: true

port: 27018             #端口號(hào)，默認(rèn)端口號(hào)為27017，因此實(shí)例2 的端口號(hào)要與之區(qū)別，實(shí)例3和4 依次往后排

配置其他實(shí)例，與實(shí)例2修改一樣，注意端口號(hào)

[root@localhost logs]# cp -p /etc/mongod2.conf /etc/mongod3.conf
[root@localhost logs]# cp -p /etc/mongod2.conf /etc/mongod4.conf

（3）啟動(dòng)服務(wù)并查看端口是否開(kāi)啟

[root@localhost logs]# mongod -f /etc/mongod.conf –shutdown                      #先關(guān)閉實(shí)例1 的服務(wù)，在開(kāi)啟
killing process with pid: 3997                                   #進(jìn)程號(hào)
[root@localhost logs]# mongod -f /etc/mongod.conf
about to fork child process, waiting until server is ready for connections.
forked process: 4867
child process started successfully, parent exiting

[root@localhost logs]# mongod -f /etc/mongod2.conf                                            #啟動(dòng)實(shí)例2 的服務(wù)
about to fork child process, waiting until server is ready for connections.
forked process: 4899
child process started successfully, parent exiting

[root@localhost logs]# mongod -f /etc/mongod3.conf                                             #啟動(dòng)實(shí)例3 的服務(wù)
about to fork child process, waiting until server is ready for connections.
forked process: 4927
child process started successfully, parent exiting

[root@localhost logs]# mongod -f /etc/mongod4.conf                                              #啟動(dòng)實(shí)例4 的服務(wù)
about to fork child process, waiting until server is ready for connections.
forked process: 4955

查看節(jié)點(diǎn)端口是否開(kāi)啟

[root@localhost logs]# netstat -ntap
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name   
tcp        0      0 0.0.0.0:27019           0.0.0.0:*               LISTEN      4927/mongod        
tcp        0      0 0.0.0.0:27020           0.0.0.0:*               LISTEN      4955/mongod        
tcp        0      0 0.0.0.0:27017           0.0.0.0:*               LISTEN      4867/mongod        
tcp        0      0 0.0.0.0:27018           0.0.0.0:*               LISTEN      4899/mongod      

（4）查看各實(shí)例能否進(jìn)入 mongodb 數(shù)據(jù)庫(kù) 

[root@localhost logs]# mongo
MongoDB shell version v3.6.7
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.6.7

[root@localhost logs]# mongo --port 27018
MongoDB shell version v3.6.7
connecting to: mongodb://127.0.0.1:27018/
MongoDB server version: 3.6.7
Server has startup warnings:

[root@localhost logs]# mongo --port 27019
MongoDB shell version v3.6.7
connecting to: mongodb://127.0.0.1:27019/
MongoDB server version: 3.6.7
Server has startup warnings:

[root@localhost logs]# mongo --port 27020
MongoDB shell version v3.6.7
connecting to: mongodb://127.0.0.1:27020/
MongoDB server version: 3.6.7

2 . 配置復(fù)制集的優(yōu)先級(jí)

（1）登錄默認(rèn)實(shí)例 mongo，重新配置4個(gè)節(jié)點(diǎn) MongoDB 復(fù)制集，設(shè)置兩個(gè)標(biāo)準(zhǔn)節(jié)點(diǎn)，有個(gè)被動(dòng)節(jié)點(diǎn)和一個(gè)仲裁節(jié)點(diǎn)，命令如下：

根據(jù)優(yōu)先級(jí)確定節(jié)點(diǎn): 優(yōu)先級(jí)為 100的為標(biāo)準(zhǔn)節(jié)點(diǎn)，端口號(hào)為 27017和27018  ，優(yōu)先級(jí)為0 的為被動(dòng)節(jié)點(diǎn)，端口號(hào)為27019；仲裁節(jié)點(diǎn)為27020

> cfg={"_id":"abc","members":[{"_id":0,"host":"192.168.213.184:27017","priority":100},{"_id":1,"host":"192.168.213.184:27018","priority":100},{"_id":2,"host":"192.168.213.184:27019","priority":0},{"_id":3,"host":"192.168.213.184:27020","arbiterOnly":true}]}
{
     "_id" : "abc",
     "members" : [
         {
             "_id" : 0,
             "host" : "192.168.213.184:27017",                   #標(biāo)準(zhǔn)節(jié)點(diǎn)，優(yōu)先級(jí)為100
             "priority" : 100
         },
         {
             "_id" : 1,
             "host" : "192.168.213.184:27018",                  #標(biāo)準(zhǔn)節(jié)點(diǎn)
             "priority" : 100
         },
         {
             "_id" : 2,
             "host" : "192.168.213.184:27019",                   #被動(dòng)節(jié)點(diǎn)，優(yōu)先級(jí)為0
             "priority" : 0
         },
         {
             "_id" : 3,
             "host" : "192.168.213.184:27020",                   #仲裁節(jié)點(diǎn)
             "arbiterOnly" : true
         }
     ]
}

> rs.initiate(cfg)                    # 初始化復(fù)制集
{
     "ok" : 1,
     "operationTime" : Timestamp(1536819122, 1),
     "$clusterTime" : {
         "clusterTime" : Timestamp(1536819122, 1),
         "signature" : {
             "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
             "keyId" : NumberLong(0)
         }
     }
}

（2）使用命令 rs.isMaster()  查看各節(jié)點(diǎn)身份

abc:PRIMARY> rs.isMaster()
{
     "hosts" : [                                         #標(biāo)準(zhǔn)節(jié)點(diǎn) 
         "192.168.213.184:27017",
         "192.168.213.184:27018"
     ],
     "passives" : [                                    #被動(dòng)節(jié)點(diǎn)
         "192.168.213.184:27019"
     ],
     "arbiters" : [                                     #仲裁節(jié)點(diǎn)
         "192.168.213.184:27020"
     ],
     "setName" : "abc",
     "setVersion" : 1,
     "ismaster" : true,
     "secondary" : false,
     "primary" : "192.168.213.184:27017",

（3）此時(shí)默認(rèn)實(shí)例已經(jīng)被選舉為活躍（primary）節(jié)點(diǎn)，可以在數(shù)據(jù)庫(kù)中插入信息了。

abc:PRIMARY> use school                                                 #活躍節(jié)點(diǎn)（primory）
switched to db school
abc:PRIMARY> db.info.insert({"id":1,"name":"lili"})                #插入兩條信息
WriteResult({ "nInserted" : 1 })
abc:PRIMARY> db.info.insert({"id":2,"name":"tom"})
WriteResult({ "nInserted" : 1 })

（4）查看日志記錄所有操作，在默認(rèn)數(shù)據(jù)庫(kù) local 中的oplog.rs   查看

abc:PRIMARY> show dbs
admin   0.000GB
config  0.000GB
local   0.000GB
school  0.000GB
abc:PRIMARY> use local                  #進(jìn)入 local 數(shù)據(jù)庫(kù)
switched to db local
abc:PRIMARY> show collections    #顯示
me
oplog.rs
replset.election
replset.minvalid
startup_log
system.replset
system.rollback.id
abc:PRIMARY> db.oplog.rs.find()     #查看日志記錄所有操作

通過(guò)日志記錄，可以找到剛才加入的兩條信息

"school.info", "ui" : UUID("2b9c93b6-a58a-4021-a2b4-33f9b19925d8"), "wall" : ISODate("2018-09-13T06:24:44.537Z"), "o" : { "_id" : ObjectId("5b9a02aca106c3eab9c639e5"), "id" : 1, "name" : "lili" } }
{ "ts" : Timestamp(1536819899, 1), "t" : NumberLong(1), "h" : NumberLong("-1447313909384631008"), "v" : 2, "op" : "i", "ns" : "school.info", "ui" : UUID("2b9c93b6-a58a-4021-a2b4-33f9b19925d8"), "wall" : ISODate("2018-09-13T06:24:59.186Z"), "o" : { "_id" : ObjectId("5b9a02bba106c3eab9c639e6"), "id" : 2, "name" : "tom" } }

3.模擬節(jié)點(diǎn)故障，如果主節(jié)點(diǎn)出現(xiàn)故障，另一個(gè)標(biāo)準(zhǔn)節(jié)點(diǎn)會(huì)選舉成為新的主節(jié)點(diǎn)。

（1）先查看當(dāng)前狀態(tài)，使用命令 rs.status()

abc:PRIMARY> rs.status()

"members" : [
         {
             "_id" : 0,                  
             "name" : "192.168.213.184:27017",               #標(biāo)準(zhǔn)節(jié)點(diǎn)，端口27017，作為主節(jié)點(diǎn)
             "health" : 1,
             "state" : 1,
             "stateStr" : "PRIMARY",
             "uptime" : 2481,
             "optime" : {
                 "ts" : Timestamp(1536820334, 1),
                 "t" : NumberLong(1)
             },

{
             "_id" : 1,
             "name" : "192.168.213.184:27018",                 #標(biāo)準(zhǔn)節(jié)點(diǎn) ，端口27018 為從節(jié)點(diǎn)
             "health" : 1,
             "state" : 2,
             "stateStr" : "SECONDARY",
             "uptime" : 1213,
             "optime" : {
                 "ts" : Timestamp(1536820324, 1),
                 "t" : NumberLong(1)
             },

{
             "_id" : 2,
             "name" : "192.168.213.184:27019",               #被動(dòng)節(jié)點(diǎn)， 端口27019位從節(jié)點(diǎn)
             "health" : 1,
             "state" : 2,
             "stateStr" : "SECONDARY",
             "uptime" : 1213,
             "optime" : {
                 "ts" : Timestamp(1536820324, 1),
                 "t" : NumberLong(1)
             },

{
             "_id" : 3,
             "name" : "192.168.213.184:27020",                     #仲裁節(jié)點(diǎn)
             "health" : 1,
             "state" : 7,
             "stateStr" : "ARBITER",
             "uptime" : 1213,
             "lastHeartbeat" : ISODate("2018-09-13T06:32:14.152Z"),

（2）模擬主節(jié)點(diǎn)故障，關(guān)閉主節(jié)點(diǎn)服務(wù)，登錄另一個(gè)標(biāo)準(zhǔn)節(jié)點(diǎn)端口 27018 ,查看麟能夠一個(gè)標(biāo)準(zhǔn)節(jié)點(diǎn)是否被選舉為主節(jié)點(diǎn)

abc:PRIMARY> exit
bye
[root@localhost logs]# mongod -f /etc/mongod.conf –shutdown                       #關(guān)閉主節(jié)點(diǎn)服務(wù)
killing process with pid: 4821
[root@localhost logs]# mongo --port 27018                                                           #指定27018 端口進(jìn)入數(shù)據(jù)庫(kù)

abc:PRIMARY> rs.status()                                                              #查看狀態(tài)

"members" : [
         {
             "_id" : 0,
             "name" : "192.168.213.184:27017",
            "health" : 0,                                                 #健康之為 0 ，說(shuō)明端口27017 已經(jīng)宕機(jī)了
             "state" : 8,
             "stateStr" : "(not reachable/healthy)",
             "uptime" : 0,
             "optime" : {
                 "ts" : Timestamp(0, 0),
                 "t" : NumberLong(-1)
             },

{
             "_id" : 1,
             "name" : "192.168.213.184:27018",               #此時(shí)另一臺(tái)標(biāo)準(zhǔn)節(jié)點(diǎn)被選舉為主節(jié)點(diǎn)，端口為 27018
             "health" : 1,
             "state" : 1,
             "stateStr" : "PRIMARY",

             "uptime" : 2812,
             "optime" : {
                 "ts" : Timestamp(1536820668, 1),
                 "t" : NumberLong(2)
             },

{
             "_id" : 2,
             "name" : "192.168.213.184:27019",
             "health" : 1,
             "state" : 2,
             "stateStr" : "SECONDARY",
             "uptime" : 1552,
             "optime" : {
                 "ts" : Timestamp(1536820668, 1),
                 "t" : NumberLong(2)
             },

{
         "_id" : 3,
         "name" : "192.168.213.184:27020",
         "health" : 1,
         "state" : 7,
         "stateStr" : "ARBITER",
         "uptime" : 1552,

其中， health 為 1 代表健康，0 代表宕機(jī)。 state 為 1 代表主節(jié)點(diǎn)，為 2 代表從節(jié)點(diǎn)

（3）將標(biāo)準(zhǔn)節(jié)點(diǎn)服務(wù)全部關(guān)閉，查看被動(dòng)節(jié)點(diǎn)是否會(huì)被選舉為主節(jié)點(diǎn)

abc:PRIMARY> exit
bye
[root@localhost logs]# mongod -f /etc/mongod2.conf –shutdown                     #關(guān)閉主節(jié)點(diǎn)服務(wù)
killing process with pid: 4853
[root@localhost logs]# mongo --port 27019                                                                #開(kāi)啟備用節(jié)點(diǎn)服務(wù)

abc:SECONDARY> rs.status()

"members" : [
         {
             "_id" : 0,
             "name" : "192.168.213.184:27017",                                   #此時(shí)兩個(gè)標(biāo)準(zhǔn)節(jié)點(diǎn)都處于宕機(jī)狀態(tài)，健康值為 0
             "health" : 0,
             "state" : 8,
             "stateStr" : "(not reachable/healthy)",
             "uptime" : 0,
             "optime" : {
                 "ts" : Timestamp(0, 0),
                 "t" : NumberLong(-1)
             },

{
             "_id" : 1,
             "name" : "192.168.213.184:27018",
             "health" : 0,
             "state" : 8,
             "stateStr" : "(not reachable/healthy)",
             "uptime" : 0,
             "optime" : {
                 "ts" : Timestamp(0, 0),
                 "t" : NumberLong(-1)
             },

{
             "_id" : 2,
             "name" : "192.168.213.184:27019",                            #被動(dòng)節(jié)點(diǎn)并沒(méi)有被選舉為主節(jié)點(diǎn)，說(shuō)明被動(dòng)節(jié)點(diǎn)不可能成為活躍節(jié)點(diǎn)
             "health" : 1,
             "state" : 2,
             "stateStr" : "SECONDARY",
             "uptime" : 3102,
             "optime" : {
                 "ts" : Timestamp(1536820928, 1),
                 "t" : NumberLong(2)
             },

{
             "_id" : 3,
             "name" : "192.168.213.184:27020",
             "health" : 1,
             "state" : 7,
             "stateStr" : "ARBITER",
             "uptime" : 1849,

（4）再次啟動(dòng)標(biāo)準(zhǔn)節(jié)點(diǎn)服務(wù)，查看主節(jié)點(diǎn)能否恢復(fù)。

abc:SECONDARY> exit
bye
[root@localhost logs]# mongod -f /etc/mongod.conf                                     #啟動(dòng)實(shí)例1 的服務(wù)
about to fork child process, waiting until server is ready for connections.
forked process: 39839
child process started successfully, parent exiting
[root@localhost logs]# mongod -f /etc/mongod2.conf                                   #啟動(dòng)實(shí)例2的服務(wù)
about to fork child process, waiting until server is ready for connections.
forked process: 39929
child process started successfully, parent exiting
[root@localhost logs]# mongo

{
             "_id" : 0,
             "name" : "192.168.213.184:27017",                           #端口27017 恢復(fù)為主節(jié)點(diǎn)，（與標(biāo)準(zhǔn)節(jié)點(diǎn)啟動(dòng)順序有關(guān)，先啟動(dòng)的為主節(jié)點(diǎn)）
             "health" : 1,
             "state" : 1,
             "stateStr" : "PRIMARY",
             "uptime" : 25,
             "optime" : {
                 "ts" : Timestamp(1536821324, 1),
                 "t" : NumberLong(3)
             },

{
         "_id" : 1,
         "name" : "192.168.213.184:27018",
         "health" : 1,
         "state" : 2,
         "stateStr" : "SECONDARY",
         "uptime" : 14,
         "optime" : {
             "ts" : Timestamp(1536821324, 1),
             "t" : NumberLong(3)
         },

{
         "_id" : 2,
         "name" : "192.168.213.184:27019",
         "health" : 1,
         "state" : 2,
         "stateStr" : "SECONDARY",
         "uptime" : 23,
         "optime" : {

{
         "_id" : 3,
         "name" : "192.168.213.184:27020",
         "health" : 1,
         "state" : 7,
         "stateStr" : "ARBITER",
         "uptime" : 23,

由此可以看出：只有標(biāo)準(zhǔn)節(jié)點(diǎn)可能被選舉為活躍節(jié)點(diǎn)（主  primary），被動(dòng)節(jié)點(diǎn)不可能成為活躍節(jié)點(diǎn)，有選舉權(quán)。仲裁節(jié)點(diǎn)不可能成為活躍節(jié)點(diǎn)。