MongoDB Replica Set Configuration: 7 Easy Steps

One of the common challenges that every growing business faces is the ability to efficiently handle the exponentially growing data. Apart from the Traditional Relational Databases, organizations are now using Document-oriented Open-source NoSQL Databases such as MongoDB. 

MongoDB Replication is an excellent feature that safeguards your data in case of any hardware or software failures. To enable this, you can easily set up the MongoDB Replica Set Configuration. These Replica Sets allow users to build extra data replicas for several purposes such as Disaster Recovery, Backup, Reporting, etc.

In this article, you will learn how to effectively set up the MongoDB Replication Setup Configuration in 7 easy steps.

Table of Content

• What is MongoDB?
• What is Replication in MongoDB?
• Why do you need Replication in MongoDB?
• What is MongoDB Replica Set Configuration?
• How to set up MongoDB Replica Set Configuration?
  • MongoDB Replica Set Configuration Step 1: Set up the hosts
  • MongoDB Replica Set Configuration Step 2: Set up hostname
  • MongoDB Replica Set Configuration Step 3: Generate Key
  • MongoDB Replica Set Configuration Step 4: Configure Replica Set
  • MongoDB Replica Set Configuration Step 5: Initiate Replication
  • MongoDB Replica Set Configuration Step 6: Adding instances to Replication
  • MongoDB Replica Set Configuration Step 7: Check the status
• Conclusion

What is MongoDB?

MongoDB is a Document-oriented Open-source NoSQL Database. It stores the data in documents and supports NoSQL Query Language to interact with data. MongoDB is very popular among organizations due to its features. MongoDB is highly elastic and lets you combine and store multivariate data without compromising on the powerful indexing options, data access, and validation rules.

NoSQL database means it does not store the data in rows and columns compared to traditional databases but instead uses documents that collect key-value pairs to store the data. Key-Value pair allows MongoDB to store the data schemaless and scale them vertically when needed without disrupting the data model. It keeps the data into a storage format known as BSON (Binary Style of JSON document). 

What is Replication in MongoDB?

Replication is the process of making copies of data across servers to ensure the high availability of data in case of failures. Replication of data ensures that the data is available all the time to users in case of any network failure or hardware failure that potentially causes data loss.

A MongoDB Replica Set is a group of mongod processes that maintain the same data set throughout. Replication in MongoDB is done via Replica Set. Replica set provides Data Redundancy and High Availability and provides fault tolerance against the loss. Replica set allows users to create additional data replicas for dedicated purposes such as Disaster Recovery, Backup, Reporting, etc.

Why do you need Replication in MongoDB?

Replication is a technique to synchronize the data across multiple server nodes. The need for Replication can be understood from the following points:

• Data Replication replicates the data across servers, thereby ensuring high data availability.
• Data Replication provides a level of fault tolerance against any data loss.
• Keeping a copy of data in another server helps users recover the data in case of network failure or data loss.
• It can also serve for disaster recovery, reporting, etc.
• It can also act as a load balancer, as it causes less load on a particular server for data retrieval.

What is MongoDB Replica Set Configuration?

The Replication of MongoDB uses a replica set to perform Replication. There are various configurations related to the replica set to replicate the data from one server to another successfully. In this blog post, you will learn about various configuration options available and how you can use them to replicate your data effectively.

You can access replica set configuration via method rs.conf(). Give below is a sample configuration document: 

{
  _id: <string>,
  version: <int>,
  term: <int>,
  protocolVersion: <number>,
  writeConcernMajorityJournalDefault: <boolean>,
  configsvr: <boolean>,
  members: [
    {
      _id: <int>,
      host: <string>,
      arbiterOnly: <boolean>,
      buildIndexes: <boolean>,
      hidden: <boolean>,
      priority: <number>,
      tags: <document>,
      secondaryDelaySecs: <int>,
      votes: <number>
    },
    ...
  ],
  settings: {
    chainingAllowed : <boolean>,
    heartbeatIntervalMillis : <int>,
    heartbeatTimeoutSecs: <int>,
    electionTimeoutMillis : <int>,
    catchUpTimeoutMillis : <int>,
    getLastErrorModes : <document>,
    getLastErrorDefaults : <document>,
    replicaSetId: <ObjectId>
  }
}

 The above configuration document contains the following elements:  

• _id: This is the name of the replica set.
• version: This is an incrementing number to distinguish various versions of Replication.
• term: An incrementing number used to distinguish revisions of the replica set configuration document from previous iterations of the configuration.
• configsvr: is a boolean term that indicates whether the replica set is used for a sharded cluster’s config servers.
• protocolVersion: It defaults to 1.
• writeConcernMajorityJournalDefault: Determines the behavior of { w: “majority”} write concern if the write concern does not explicitly specify the journal option j.
• members: This array element contains the information about various replication members (servers) included in the replication set. It stores id, hostname, indexes, priority, etc.
• settings: It contains optional settings that are applied to the whole replica set.

You can find more information about these configuration options from the Official MongoDB Documentation page.

How to set up MongoDB Replica Set Configuration?

Setting up Replication in MongoDB contains fairly simple steps and is easy to learn. Ensure that MongoDB is installed on all nodes where you want to replicate the data. For MongoDB installation, you can refer to the guide available in the Official MongoDB Documentation. You can now follow the step-by-step procedure to set up Replication in MongoDB:

• MongoDB Replica Set Configuration Step 1: Set up the hosts
• MongoDB Replica Set Configuration Step 2: Set up hostname
• MongoDB Replica Set Configuration Step 3: Generate Key
• MongoDB Replica Set Configuration Step 4: Configure Replica Set
• MongoDB Replica Set Configuration Step 5: Initiate Replication
• MongoDB Replica Set Configuration Step 6: Adding instances to Replication
• MongoDB Replica Set Configuration Step 7: Check the status

MongoDB Replica Set Configuration Step 1: Set up the hosts

For this example, the following nodes are used to replicate the data: 

192.168.0.29 mongo-db1 
192.168.0.30 mongo-db2
192.168.0.31 mongo-db3

Add the above IP address to each node’s/etc/hosts file. Please ensure that all the three IPs need to be in each node’s/etc/hosts file.

MongoDB Replica Set Configuration Step 2: Set up hostname

On each node, rename the hostname to be identified via a name, not just by IP address.

$ sudo vim /etc/hostname     ## On Node1 
mongo-db1 
$ sudo vim /etc/hostname     ## On Node2
mongo-db2
$ sudo vim /etc/hostname     ## On Node3
mongo-db3

MongoDB Replica Set Configuration Step 3: Generate Key

Keys will help to communicate nodes without the requirement of an external passcode.

To generate the key, execute the given below commands:

On Node 1(mongo-db1)
# mkdir -p /etc/mongodb/keys/
# openssl rand -base64 756 > /etc/mongodb/keys/mongo-key
# chmod 400 /etc/mongodb/keys/mongo-key
# chown -R mongodb:mongodb /etc/mongodb

Now, you can copy the generated key file to all other nodes at the same location i.e. /etc/mongodb/keys .

MongoDB Replica Set Configuration Step 4: Configure Replica Set

Now that you have all the configurations done on the nodes, one last step is to add the IP addresses of the nodes and provide a replication set name. The MongoDB configuration file can be found at /etc/mongo.conf.

On node 1 => mongo-db1
# network interfaces
net:
  port: 27017
  bindIp: 192.168.0.29
#security:
security:
 authorization: enabled
 keyFile:  /etc/mongodb/keys/mongo-key
#replication:
replication:
  replSetName: "replicaset-01"

Perform the same thing on the other two nodes.

Once the changes are done, you can restart the MongoDB services by running the following command: 

sudo systemctl restart mongod

MongoDB Replica Set Configuration Step 5: Initiate replication

Log in to the primary node 192.168.0.29 .

$ mongo
> rs.initiate()

MongoDB Replica Set Configuration Step 6: Adding Instances to Replica set

Once the replication REPL is started, it’s time to add nodes to the replication set by the following command:

rs.add(“mongo-db2:27017”)
rs.add(“mongo-db3:27017”)

Once you add the nodes, you will see the output as {‘ok’:1}, which indicates a successful addition of nodes in the replica set.

MongoDB Replica Set Configuration Step 7: Check the Status

The status of the replication set can be seen from the following command:

rs.status()

The above command will result in the following output:

{ 
"set" : "myitsocial", 
"date" : ISODate("2022-02-10T06:15:02Z"), 
"myState" : 1, 
"members" : [ 
   { 
      "_id" : 0, 
      "name" : "192.168.0.29:27017", 
      "health" : 1, 
      "state" : 1, 
      "stateStr" : "PRIMARY", 
      "uptime" : 303165, 
      "optime" : Timestamp(1644516902, 1), 
      "optimeDate" : ISODate("2022-02-10T06:15:02Z"), 
      "self" : true 
   }, 
   { 
      "_id" : 1, 
      "name" : "192.168.0.30:27017", 
      "health" : 1, 
      "state" : 2, 
      "stateStr" : "SECONDARY", 
      "uptime" : 302985, 
      "optime" : Timestamp(1644516902, 1), 
      "optimeDate" : ISODate("2022-02-10T06:15:02Z"), 
      "lastHeartbeat" : ISODate("2022-02-10T06:15:02Z"), 
      "lastHeartbeatRecv" : ISODate("2014-08-12T06:15:02Z"), 
      "pingMs" : 0, 
   "syncingTo" : "10.20.30.40:27017" 
   },
   { 
      "_id" : 2, 
      "name" : "192.168.0.31:27017", 
      "health" : 1, "state" : 2, 
      "stateStr" : "SECONDARY", 
      "uptime" : 302985, 
      "optime" : Timestamp(1644516902, 1), 
      "optimeDate" : ISODate("2022-02-10T06:15:02Z"), 
      "lastHeartbeat" : ISODate("2022-02-10T06:15:02Z"), 
      "lastHeartbeatRecv" : ISODate("2022-02-10T06:15:02Z"), 
      "pingMs" : 0, 
      "syncingTo" : "192.168.0.29:27017" 
   } 
], 
"ok" : 1 
} 

Conclusion

In this article, you have learned how to set up MongoDB Replica Set Configuration with help of a step-by-step procedure. MongoDB prevents the loss of any data via its Replication feature. Using Replica sets, MongoDB provides Data Redundancy, High Availability, and Fault-tolerance by allowing users to create additional data replicas for dedicated purposes such as Disaster Recovery, Backup, Reporting, etc.

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