Master-slave architecture :
mongodb supports the traditional master-slave architecture. The master node is responsible for reading and writing data, and the slave has no write permission. There is no automatic failover function, you need to specify the master and slave sides, and it is not recommended for use in production.
Advantages of master-slave replication:
The slave server can perform query work, reducing the access pressure of the master server
Perform backups on the slave to avoid locking the master's data during backups
When the master server fails, it can quickly switch to the slave server to reduce downtime.
MongoDB supports complete failover and redundancy through asynchronous replication in multiple machines. Only one of multiple machines is used for write operations at the same time, which provides mongoDB with data consistency guarantee. The machine that plays the primary role can Distribute read operations to slave machines.
Configuration of master-slave architecture
Environment: CentOS6.5 MongoDB3.4
master configuration file
master.conf
dbpath=/data/mongo/master logpath=/var/log/mongo/master/mongodb.log port=27017 bind_ip=127.0.0.1 master=true fork=true //Run mongodb service in the background
slave configuration file
dbpath=/data/mongo/slave logpath=/var/log/mongo/slave/mongodb.log port=27018 bind_ip=127.0.0.1 slave=true fork=true //Run mongodb service in the background source=127.0.0.1:27017 //Configure the main ip and port
Start master and slave respectively
mongo --config master.conf mongo --config slave.conf
Log in to master and slave respectively
mongo 127.0.0.1:27017 mongo 127.0.0.1:27018
Execute show dbs on the master
> show dbs admin 0.000GB local 0.005GB
Executing show dbs on the slave reports an error
> show dbs
2018-04-19T11:31:35.982+0800 E QUERY [thread1] Error: listDatabases failed:{
"ok" : 0,
"errmsg" : "not master and slaveOk=false",
"code" : 13435,
"codeName" : "NotMasterNoSlaveOk"
} :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
Mongo.prototype.getDBs@src/mongo/shell/mongo.js:62:1
shellHelper.show@src/mongo/shell/utils.js:782:19
shellHelper@src/mongo/shell/utils.js:672:15
@(shellhelp2):1:1
This error is because there is no read and write permission on the slave by default, you can execute the following command on the slave to solve
> rs.slaveOk() //The setting method of version 2.6 is different > show dbs admin 0.000GB local 0.000GB
test:
Create database masterslavetest on main repository and create some test data
> use masterslave
switched to db masterslave
> for (i = 5000; i < 100000; i++) {
... db.users.insert({
... "i": i,
... "userName": "user" + i,
...
... "age": Math.floor(Math.random() * 120),
... "created": new Date(),
... total: Math.floor(Math.random() * 100) * i
... })
... }
WriteResult({ "nInserted" : 1 })
Execute the following commands on the two instances respectively, and you can see that the data on the two databases is consistent. At this time, when CRUD and other operations are performed on the master database, the data from the slave database is still consistent with the master database.
db.users.find()
The above command is also executed on the slave
Test adding a piece of data to the slave node to see
> db.mycoll.insert({"i":9999,"username":"test","age":30})
WriteResult({ "writeError" : { "code" : 10107, "errmsg" : "not master" } })
It can be seen that the slave node does not have write permission.
Turn off the mongodb process on the master and see
> show dbs
2018-04-19T11:58:43.464+0800 E QUERY [thread1] Error: listDatabases failed:{
"ok" : 0,
"errmsg" : "not master and slaveOk=false",
"code" : 13435,
"codeName" : "NotMasterNoSlaveOk"
} :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
Mongo.prototype.getDBs@src/mongo/shell/mongo.js:62:1
shellHelper.show@src/mongo/shell/utils.js:782:19
shellHelper@src/mongo/shell/utils.js:672:15
@(shellhelp2):1:1
> rs.slaveOk()
>
>
> show dbs
admin 0.000GB
local 0.000GB
masterslave 0.005GB
It can be known from the above test that if the master node hangs, the slave node cannot automatically take over the service and becomes the master role. You need to manually modify the configuration file, set it to master, and restart the service to read and write.