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Replication Sets is a replication function based on master/slave replication mechanism, which performs asynchronous synchronization of the same data, so that multiple machines have multiple copies of the same data. Due to automatic failover and recovery features, when the master database goes down, it automatically switches to other backup servers without user intervention. A cluster can support up to 7 servers, and any node can be the master node. All write operations are distributed to the master node, while read operations can be performed on any node, achieving read and write separation and increasing load.

Limited resources to test a VM open 3 instances:

Environment: centos7.0

192.168.1.21:20011 P

192.168.1.21:20012 S

192.168.1.21:20013 A

mongodb verson:3.2

Construction process:

1. Download the package and extract it

2. Add relevant directory files

[root@localhost mongodb27017]# ll

Total consumption 8

drwxr-xr-x. 2 root root 4096 December 17 00:59 bin

drwxr-xr-x. 2 root root 30 Dec 17 10:47 conf

drwxr-xr-x 4 root root 4096 Dec 17 11:19 data

drwxr-xr-x. 2 root root 20 December 17 01:13 key

drwxr-xr-x. 2 root root 23 Dec 17 10:20 logs

#3 The same configuration

3. Unzip all files in the bin directory under the package to cp to the bin directory currently created.

4. The configuration files of 3 instances are consistent.

[root@localhost conf]# cat mongodb27017.conf

port=20011#port of each instance, configured according to actual situation

dbpath=/export/mongodb27017/data #Data directory

The requested URL/logs/mongod.log was not found on this server.

fork=true

logappend=true

#keyFile=/export/mongodb27017/key/mongodb#

nohttpinterface=true

replSet=mongodb ##Name of replSet,

5. Start three instances:

/export/mongodb27018/bin/mongod -f /export/mongodb27018/conf/mongodb27018.conf

/export/mongodb27019/bin/mongod -f /export/mongodb27019/conf/mongodb27019.conf

/export/mongodb27017/bin/mongod -f /export/mongodb27017/conf/mongodb27017.conf

#You need to copy the files under the bin directory of the decompression package to these 3 startup directories respectively, or one can be used as basedir, and the others can be separated.

6. Configure replication set

/export/mongodb27017/bin/mongo --port 20011#Enter the database according to your actual definition

1. Configure member relationships:

config = {_id:"mongodb", members:[{_id:0,host:"192.168.1.21:20011", priority : 3}]}(priority 3 is given,mongodb is the name of the replication set)

2. Initialize:

>rs.initiate(config);

3. Add standby node and arbitration node

rs.add("192.168.1.21:20012") Add spare node

rs.addArb("192.168.1.21:20013") Add arbitration node

rs.status()#View status

rs.conf()#View replica set members and their priority (favor the order of members, priority from 1-100, the larger the priority)

config=rs.conf() for priority setting

config.members[0].priority = 3 Sets the primary node priority to 3

config.members[1].priority = 2 Set standby priority to 2

config.members[2].priority = 1 Sets the arbitration node priority to 1

rs.remove("ip:port") Remove existing members

rs.reconfig(config) Save configuration, take effect

7. Set standby node to slave

mongodb:SECONDARY> show dbs

2016-12-17T12:26:22.621+0800 E QUERY [thread1] Error: listDatabases failed:{ "ok" : 0, "errmsg" : "not master and slaveOk=false", "code" : 13435 } :

Log in to the 20012 instance and execute:rs.slaveOk()

8. Test whether the master node can be switched when it is down.

Summary:

MongoDB's master-slave mode is actually a single-copy application, without good scalability and fault tolerance. The replica set has multiple replicas to ensure fault tolerance. Even if one replica is hung up, there are still many replicas. Moreover, the first problem above,"If the primary node is hung up, the whole cluster will automatically switch." If the node is hung up, it will re-elect a new primary node. For ordinary business can meet, but high concurrency, replication set is unable to meet, you need shard, to achieve cluster high availability, you can use LVS or other.

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