何为复制集？
复制集是额外的数据副本，是跨多个服务器同步数据的过程，复制集提供了冗余并增加了数据可用性，通过复制集可以对硬件故障和中断的服务进行恢复。
复制集主从同步的原理和类似，主节点记录在其上的所有操作到oplog中，从节点定期轮询主节点获取这些操作，然后对自己的数据副本执行这些操作，从而保证从节点的数据与主节点一致。
复制集的优势如下：
（1）让数据更安全
（2）高数据可用性（24*7）
（3）灾难恢复
（4）无停机维护（如备份、索引重建、故障转移）
（5）读缩放（额外的副本读取）
（6）副本集对应用程序是透明。
MongoDB复制集结构原理图分析
.mongodb的复制集至少需要两个节点。其中一个是主节点(Primary)，负责处理客户端请求，其余的都是从节点(Secondary)，负责复制主节点上的数据。
mongodb各个节点常见的搭配方式为：一主一从或一主多从。
客户端在主节点写入数据，在从节点读取数据，主节点与从节点进行数据交互，保障数据的一致性。如果其中一个节点出现故障，其他节点马上会将业务接过来而无需停机操作
复制集的特点：
1.N 个节点的集群
2.任何节点可作为主节点
3.所有写入操作都在主节点上
4.自动故障转移
5.自动恢复
MongoDB复制集部署
在一台CentOS7主机上使用yum在线安装Mongodb，并创建多实例，进行部署MongoDB复制集
首先配置网络YUM源，baseurl（下载路径）指定为mongodb官网提供的yum仓库
vim /etc/yum.repos.d/mongodb.repo
[mongodb-org]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.6/x86_64/ #指定获得下载的路径
gpgcheck=1 #表示对从这个源下载的rpm包进行校验
enabled=1 #表示启用这个源。
gpgkey=https://www.mongodb.org/static/pgp/server-3.6.asc
重新加载yum源，并使用yum命令下载安装mongodb
yum list
yum -y install mongodb-org
准备4个实例，暂时开启3个， 1主2从 再额外添加群集（追加实例）也可以撤销实例
创建数据文件和日志文件存储路径，并赋予权限
[root@localhost ~]# mkdir -p /data/mongodb{2,3,4}[root@localhost ~]# mkdir /data/logs[root@localhost ~]# touch /data/logs/mongodb{2,3,4}.log[root@localhost ~]# chmod 777 /data/logs/mongodb*[root@localhost ~]# ll /data/logs/总用量 0-rwxrwxrwx. 1 root root 0 9月 15 22:31 mongodb2.log-rwxrwxrwx. 1 root root 0 9月 15 22:31 mongodb3.log-rwxrwxrwx. 1 root root 0 9月 15 22:31 mongodb4.log
编辑4个MongoDB实例的配置文件
先编辑yum安装的默认实例的配置文件/etc/mongod.conf，指定监听IP，端口默认为27017，开启replication参数配置，replSetName：true（自定义）
[root@localhost ~]# vim /etc/mongod.conf
# mongod.conf
# for documentation of all options, see:
## where to write logging data.
systemLog: destination: file logAppend: true path: /var/log/mongodb/mongod.log# Where and how to store data.
storage: dbPath: /var/lib/mongo journal: enabled: true# engine:# mmapv1:# wiredTiger:# how the process runs
processManagement: fork: true # fork and run in background pidFilePath: /var/run/mongodb/mongod.pid # location of pidfile timeZoneInfo: /usr/share/zoneinfo# network interfaces
net:port: 27017 #默认端口 bindIp: 0.0.0.0 #监听任意地址
#security:
#operationProfiling:
replication: #去掉前面的“#”注释，开启该参数设置replSetName: true #设置复制集名称
复制配置文件给其他实例，并将mongodb2.conf 中的port参数配置为27018，mongod3.conf中的port参数配置为27019，mongod4.conf中的port参数配置为27020。 同样也将dbpath和logpath参数修改为对应的路径值
cp /etc/mongod.conf /etc/mongod2.conf
cp /etc/mongod2.conf /etc/mongod3.conf
cp /etc/mongod2.conf /etc/mongod4.conf
实例2的配置文件mongodb2.conf 修改
vim /etc/mongod2.conf
systemLog:
destination: file
logAppend: true
path: /data/logs/mongodb2.log
storage:
dbPath: /data/mongodb/mongodb2
journal:
enabled: true
port: 27018
bindIp: 0.0.0.0 # Listen to local interface only, comment to listen on all interfaces.
#security:
#operationProfiling:
replication:replSetName: true
实例3的配置文件mongodb3.conf 修改
vim /etc/mongod3.conf
systemLog:
destination: file
logAppend: true
path: /data/logs/mongodb3.log
storage:
dbPath: /data/mongodb/mongodb3
journal:
enabled: true
port: 27019
bindIp: 0.0.0.0 # Listen to local interface only, comment to listen on all interfaces.
#security:
#operationProfiling:
replication:replSetName: true
实例4的配置文件mongodb4.conf 修改
vim /etc/mongod4.conf
systemLog:
destination: file
logAppend: true
path: /data/logs/mongodb4.log
storage:
dbPath: /data/mongodb/mongodb4
journal:
enabled: true
port: 27020
bindIp: 0.0.0.0 # Listen to local interface only, comment to listen on all interfaces.
#security:
#operationProfiling:
replication:replSetName: true
启动mongodb各实例
[root@localhost ~]# mongod -f /etc/mongod.conf
about to fork child process, waiting until server is ready for connections.forked process: 93576child process started successfully, parent exiting[root@localhost ~]# mongod -f /etc/mongod2.conf about to fork child process, waiting until server is ready for connections.forked process: 93608child process started successfully, parent exiting[root@localhost ~]# mongod -f /etc/mongod3.conf about to fork child process, waiting until server is ready for connections.forked process: 93636child process started successfully, parent exiting[root@localhost ~]# mongod -f /etc/mongod4.conf about to fork child process, waiting until server is ready for connections.forked process: 93664child process started successfully, parent exiting[root@localhost ~]# netstat -antp | grep mongod //查看mongodb进程状态tcp 0 0 0.0.0.0:27019 0.0.0.0:* LISTEN 93636/mongod tcp 0 0 0.0.0.0:27020 0.0.0.0:* LISTEN 93664/mongod tcp 0 0 0.0.0.0:27017 0.0.0.0:* LISTEN 93576/mongod tcp 0 0 0.0.0.0:27018 0.0.0.0:* LISTEN 93608/mongod
配置三个节点的复制集
[root@localhost ~]# mongo //进入其中一个实例MongoDB shell version v3.6.7
connecting to: mongodb://127.0.0.1:27017MongoDB server version: 3.6.7> rs.status() //查看复制集状态，提示复制集还未配置{
"info" : "run rs.initiate(...) if not yet done for the set", "ok" : 0, "errmsg" : "no replset config has been received", "code" : 94, "codeName" : "NotYetInitialized", "operationTime" : Timestamp(0, 0), "$clusterTime" : { "clusterTime" : Timestamp(0, 0), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }> cfg={"_id":"true","members":[{"_id":0,"host":"192.168.195.137:27017"},{"_id":1,"host":"192.168.195.137:27018"},{"_id":2,"host":"192.168.195.137:27019"}]} // 定义cfg初始化参数 {
"_id" : "true", "members" : [ { "_id" : 0, "host" : "192.168.195.137:27017" }, { "_id" : 1, "host" : "192.168.195.137:27018" }, { "_id" : 2, "host" : "192.168.195.137:27019" } ]}> rs.initiate(cfg) //初始化并启动复制集
{"ok" : 1}
true:PRIMARY> rs.status() //再次查看复制集的状态信息{
"set" : "true", "date" : ISODate("2018-09-15T15:39:48.426Z"), "myState" : 1, "term" : NumberLong(1), "syncingTo" : "", "syncSourceHost" : "", "syncSourceId" : -1, "heartbeatIntervalMillis" : NumberLong(2000), "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) }, "readConcernMajorityOpTime" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) }, "appliedOpTime" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) }, "durableOpTime" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) } }, "members" : [ { "_id" : 0, "name" : "192.168.195.137:27017", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", //此节点成为主节点 "uptime" : 1371, "optime" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) },....................
{ "_id" : 1, "name" : "192.168.195.137:27018", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", //此节点为从节点 "uptime" : 18, "optime" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) },...................
{ "_id" : 2, "name" : "192.168.195.137:27019", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", //此节点为从节点 "uptime" : 18, "optime" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1537025984, 1), "t" : NumberLong(1) },
添加节点
true:PRIMARY> rs.add("192.168.195.137:27020")
true:PRIMARY> rs.status()
..............
{
"_id" : 3, "name" : "192.168.195.137:27020", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 8, "optime" : { "ts" : Timestamp(1537026818, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1537026818, 1), "t" : NumberLong(1) },.................
删除节点
true:PRIMARY> rs.remove("192.168.195.137:27020")
模拟故障自动转移切换
[root@localhost ~]# mongod -f /etc/mongod.conf --shutdown //关闭主节点服务killing process with pid: 93576
[root@localhost ~]# mongo --port 27018 //进入其中一个从节点MongoDB shell version v3.6.7connecting to: mongodb://127.0.0.1:27018/MongoDB server version: 3.6.7true:PRIMARY> rs.status() //查看复制集信息
..............
}, "members" : [ { "_id" : 0, "name" : "192.168.195.137:27017", //原来的主节点健康值为0 "health" : 0, "state" : 8, "stateStr" : "(not reachable/healthy)", "uptime" : 0, "optime" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) }, "optimeDurable" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) },.................
{ "_id" : 1, "name" : "192.168.195.137:27018", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", //此节点切换成主节点 "uptime" : 2657, "optime" : { "ts" : Timestamp(1537027275, 1), "t" : NumberLong(2) },................
{ "_id" : 2, "name" : "192.168.195.137:27019", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 1312, "optime" : { "ts" : Timestamp(1537027275, 1), "t" : NumberLong(2) }, "optimeDurable" : { "ts" : Timestamp(1537027275, 1), "t" : NumberLong(2) },
手动进行主从切换
[root@localhost ~]# mongod -f /etc/mongod.conf #开启刚才关闭的端口为27017的节点实例
about to fork child process, waiting until server is ready for connections.
forked process: 94723child process started successfully, parent exiting[root@localhost ~]# mongo --port 27018 #进入主节点服务器实例MongoDB shell version v3.6.7connecting to: mongodb://127.0.0.1:27018/MongoDB server version: 3.6.7
true:PRIMARY> rs.freeze(30) //暂停30s不参与选举
true:PRIMARY> rs.stepDown(60.30) //交出主节点位置，维持从节点状态不少于60秒，等待30秒使主节点和从节点日志同步
true:SECONDARY> rs.status() //可以看到本实例已经切换成从节点
................
"members" : [ { "_id" : 0, "name" : "192.168.195.137:27017", // 端口27017的节点变成了主节点 "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 167, "optime" : { "ts" : Timestamp(1537027620, 1), "t" : NumberLong(3) }, "optimeDurable" : { "ts" : Timestamp(1537027620, 1), "t" : NumberLong(3) },..................
{ "_id" : 1, "name" : "192.168.195.137:27018", // 端口27018的节点变成了从节点"health" : 1,
"state" : 2, "stateStr" : "SECONDARY", "uptime" : 2997, "optime" : { "ts" : Timestamp(1537027620, 1), "t" : NumberLong(3) },...................
{ "_id" : 2, "name" : "192.168.195.137:27019", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 1651, "optime" : { "ts" : Timestamp(1537027620, 1), "t" : NumberLong(3) }, "optimeDurable" : { "ts" : Timestamp(1537027620, 1), "t" : NumberLong(3) },