MongoDB replication (Replica set)

Copy (replica set) what is replication

• Replication provides redundant backups of data, stores copies of data on multiple servers, improves data availability, and ensures data security
• Replication also allows recovery of data from hardware failures and service outages

Why do you want to copy

• Data backup
• Data disaster recovery
• Read/write separation
• High (24* 7) data availability
• No Downtime Maintenance
• Replica sets are transparent to applications

How replication works

• Replication requires a minimum of two nodes A, B ...
• A is the master node responsible for processing client requests
• The rest is from the node, which is responsible for replicating the data on the master node
• The common collocation methods of nodes are: one master, one from, one main and many from
• The master node records all operations on it, obtains these operations from the node periodically polling the master node, and then performs these operations on its own copy of the data, ensuring that the data from the node is consistent with the primary node
• Data interaction between primary node and slave node ensures data consistency

Features of replication

• N-node clusters
• Any node can be used as the master node
• All write operations are on the primary node
• Auto Fail-Over
• Automatic recovery

Setting Up Replication nodes

• The next operation will need to open multiple terminal windows, and may be connected to more than one Ubuntu host, it will appear a bit messy, it is recommended to implement in Xshell
• Step1: Create database directory T1, t2
• Demo in Desktop directory, other directories can also, pay attention to the permissions can be

mkdir t1mkdir t2

• Step2: Start Mongod with the following format, note that the name of Replset is consistent

mongod --bind_ip 192.168.196.128 --port 27017 --dbpath ~/Desktop/t1 --replSet rs0mongod --bind_ip 192.168.196.128 --port 27018 --dbpath ~/Desktop/t2 --replSet rs0

• Step3: Connect to master server, set 192.168.196.128:27017 as primary server here

mongo --host 192.168.196.128 --port 27017

• STEP4: Initialization

rs.initiate()

• After initialization is complete, the prompt is as follows:

• Step5: View current status

rs.status()

• Current state such as:

• STEP6: Adding replica Sets

rs.add(‘192.168.196.128:27018‘)

• STEP7: After the replica set has been added successfully, the current state is as follows:

• STEP8: Connecting a second MONGO service

mongo --host 192.168.196.128 --port 27018

• After the connection is successful, the prompt is as follows:

• STEP9: Inserting data into the primary server

use test1for(i=0;i<10;i++){db.t1.insert({_id:i})}db.t1.find()

• STEP10: Inserting queries from the server
• Note: If you are reading from a server, you need to set Rs.slaveok ()

rs.slaveOk()db.t1.find()

Other instructions

• Remove from node

rs.remove(‘192.168.196.128:27018‘)

• After shutting down the primary server and restarting, you will find that the original slave server has changed from the server, the newly started server (the original slave server) to the slave server

MongoDB replication (Replica set)