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How to Setup a MongoDB Cluster

How to Setup a MongoDB Cluster

  • ITOps & DevOps
5 minute read Updated Mar 6, 2019

Written by: Walker Rowe

TL;DR Summary: Setting up a MongoDB cluster involves installing a config server, query router, and shard server. The process includes configuring each server, ensuring proper networking, and enabling sharding for data distribution. Key steps include editing configuration files, starting services, and checking logs for errors. For detailed instructions, follow the provided steps and links to additional MongoDB resources.

  • Install config server, query router, and shard server.
  • Enable sharding for data distribution across the cluster.

Here we show how to set up a MongoDB cluster. In the previous post we showed how to install it on one machine.

There are three pieces to install:

  1. config server
  2. query router
  3. shard server, i.e., database

Looking at the diagram below, the mongos process runs as a router, meaning it tells clients where to look for data. Data is spread across the cluster based on sharing. Sharding is the assignment of records to servers based on the hashed value of some index. The config server hold configuration information.

Config server

Install MongoDB

Technically, to make a MongoDB a cluster just means to three layers of the MongoDB architecture as separate processes. You could do this for academic purposes on one machine. But here we use two.

We will install the router and config servers on 172.31.46.15 and the shard server on 172.31.47.43. For simplicity, let's call the first server the config server and the second server the database server.

Do not use apt-get to install MongoDB as that is not the current version, usually. Instead follow the steps below. Note that this installs mongod (config and shard server), mongos (router), and mongo client as three separate packages.

Open firewall ports 27017, 27018, and 27019 between the two servers.

You need the all three packages on the config server but only mongodb-org-server on the database server. On Ubuntu, install them like this.

    wget https://repo.mongodb.org/apt/ubuntu/dists/xenial/mongodb-org/4.0/multiverse/binary-amd64/mongodb-org-server_4.0.5_amd64.deb

sudo dpkg -i mongodb-org-server_4.0.5_amd64.deb

wget https://repo.mongodb.org/apt/ubuntu/dists/xenial/mongodb-org/4.0/multiverse/binary-amd64/mongodb-org-shell_4.0.5_amd64.deb

sudo dpkg -i mongodb-org-shell_4.0.5_amd64.deb

wget https://repo.mongodb.org/apt/ubuntu/dists/xenial/mongodb-org/4.0/multiverse/binary-amd64/mongodb-org-mongos_4.0.5_amd64.deb

 sudo dpkg -i mongodb-org-mongos_4.0.5_amd64.deb

Note that if you mess up any step, remove the server and then erase the data file library, /var/lib/mongodb. If you don't erase the data files when you reinstall the software it will keep the previous configuration and thus restore any mistakes you made.

Login to the config server.

To set up all three servers we will repeat the same 4 steps on each server:

  1. Edit config file
  2. Start process
  3. Check log for errors
  4. Log into shell to do further configuration

Now, on the config server edit the config file. Note for the sake of simplicity we make each config file have a descriptive name:

Login to the config server.

    sudo vim /etc/mongodConfig.conf

Paste in the text below. First, we explain some of the fields:

path: /var/log/mongodb/mongodConfig.log
 For each process we give the log a name that makes clear which process it is for. 
port: 27019
bindIp: 172.31.46.15
 By default the config server will run on port 2019 in a clustered configuration. We make that explicit here so it not necessary to remember that. Also the IP address is a non-loopback address.That is so that other servers can find this server. 
sharding:
clusterRole: configsvr
 Sharding means to distribute data according to some hashing scheme. Here we tell MongoDB that this server is a config server, as opposed to a sharing server. 
replication:
replSetName: ConfigReplSet
 This means to replicate this configuration data. We use rs.() functions to add other replicas. We can use any name.

Paste this text into /etc/mongodConfig.conf:

Start the process:

    storage:
  dbPath: /var/lib/mongodb
  journal:
    enabled: true

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongodConfig.log

net:
  port: 27019
  bindIp: 172.31.46.15

sharding:
  clusterRole: configsvr

replication:
  replSetName: ConfigReplSet

Start the process:

    sudo mongod --config /etc/mongodConfig.conf&

Check the logs for errors:

    sudo tail -100 /var/log/mongodb/mongodConfig.log

Log in to the shell:

    mongo 172.31.46.15:27019

Turn on replication with rs.initiate() and check the status with rs.status(). Notice that is picked up the name of the replication set we configured in the config file, ConfigReplSet.

    > rs.initiate()
{
	"info2" : "no configuration specified. Using a default configuration for the set",
	"me" : "172.31.46.15:27019",
	"ok" : 1,
	"operationTime" : Timestamp(1548598138, 1),
	"$gleStats" : {
		"lastOpTime" : Timestamp(1548598138, 1),
		"electionId" : ObjectId("000000000000000000000000")
	},
	"lastCommittedOpTime" : Timestamp(0, 0),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1548598138, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}
ConfigReplSet:SECONDARY> rs.status()
{
	"set" : "ConfigReplSet",

Configure Query Router

Edit the config file:

    sudo vim /etc/mongoRouter.conf

Paste in the text below. Notice:

configDB: ConfigReplSet/172.31.46.15:27019
 This tells the query router where to find the config server and their replica sets. 
    systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongoRouter.log

net:
  port: 27017
  bindIp: 172.31.46.15

sharding:
  configDB: ConfigReplSet/172.31.46.15:27019

Start the service. Notice the s in mongos. This is the query router process.

    sudo mongos --config /etc/mongoRouter.conf&

Check the log and look for errors:

    mongo 172.31.46.15:27017

Configure Shard

Log into database server.

    sudo vim /etc/mongodShard.conf

Paste in the text below. Notice that:

Start the process.

clusterRole: shardsvr
 Means this will be a shard server, as opposed to a config server. 
replSetName: ShardReplSet
 This means to replicate the data.  In the config server we told it to replicate the configuration. 
port: 27018
 By default shard servers run on port 27018. So we make that explicit so we don't have to remember that. 
    storage:
  dbPath: /var/lib/mongodb
  journal:
    enabled: true

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongodShard.log

net:
  port: 27018 
  bindIp: 172.31.47.43

sharding:
  clusterRole: shardsvr

replication:
  replSetName: ShardReplSet

Start the process.

    sudo mongod --config /etc/mongodShard.conf&

Check the log for errors.

Log into the shell.

    sudo tail -f /var/log/mongodb/mongodShard.log

Log into the shell.

    mongo 172.31.47.43:2018

Turn on replications with rs.initiate() and then check the status with rs.status(). Notice the name ShardReplSet. We could use any name as long as we use the same name across all shards in the cluster.

    rs.initiate()
{
	"info2" : "no configuration specified. Using a default configuration for the set",
	"me" : "172.31.47.43:27018",
	"ok" : 1,
	"operationTime" : Timestamp(1548602253, 1),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1548602253, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}
ShardReplSet:SECONDARY> rs.status()
{
	"set" : "ShardReplSet",

Add Shard to Cluster

Go back to config server and connect to router:

    mongo 172.31.46.15:27017

Paste all of the followings commands into the shell:

    sh.addShard( "ShardReplSet/172.31.47.43:27018")

{
	"shardAdded" : "ShardReplSet",
	"ok" : 1,
	"operationTime" : Timestamp(1548602529, 4),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1548602529, 4),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

Create a database named books then enable sharding.

    use books
switched to db books

sh.enableSharding("books")

{
	"ok" : 1,
	"operationTime" : Timestamp(1548602601, 6),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1548602601, 6),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

Create a collection.

    db.createCollection("collection")


{
	"ok" : 1,
	"operationTime" : Timestamp(1548602659, 5),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1548602659, 5),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

Create an index. We will index the field isbn in descending order.

Add one record.

    db.collection.createIndex( { isbn: -1 } )


{
	"raw" : {
		"ShardReplSet/172.31.47.43:27018" : {
			"createdCollectionAutomatically" : false,
			"numIndexesBefore" : 1,
			"numIndexesAfter" : 2,
			"ok" : 1
		}
	},
	"ok" : 1,
	"operationTime" : Timestamp(1548602670, 9),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1548602670, 9),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

Add one record.

    db.collection.insertOne( { isbn: 100 } )


{
	"acknowledged" : true,
	"insertedId" : ObjectId("5c4dcd69e83741cb900b46f8")
}

Turn on sharding for the collection.

    sh.shardCollection("books.collection", { isbn : "hashed" } )

{
	"collectionsharded" : "books.collection",
	"collectionUUID" : UUID("0d10320b-3086-472e-a3ac-4be67fae21f9"),
	"ok" : 1,
	"operationTime" : Timestamp(1548603537, 12),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1548603537, 12),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

Now verify that data is distributed across cluster as shown below. Of course we only have one database server, so it just shows one. In another blog post we will show how to add more servers.

    db.collection.getShardDistribution()

Shard ShardReplSet at ShardReplSet/172.31.47.43:27018
 data : 0B docs : 0 chunks : 2
 estimated data per chunk : 0B
 estimated docs per chunk : 0

Totals
 data : 0B docs : 0 chunks : 2
 Shard ShardReplSet contains NaN% data, NaN% docs in cluster, avg obj size on shard : NaNGiB

MongoDB Guide

  1. MongoDB Overview: Getting Started with MongoDB
  2. How to Install MongoDB on Ubuntu and Mac
  3. Creating a Database in MongoDB
  4. MongoDB Shell Basic Commands
  5. MongoDB Compass: Using the Mongo GUI
  6. MongoDB Role-Based Access Control (RBAC) Explained
  7. MongoDB Projection & Projection Operators Explained
  8. MongoDB Aggregate Functions Explained
  9. MongoDB Sorting: sort() Method & Examples
  10. Using Push & Pull Operators in MongoDB
  11. How To Use MongoDB $unwind
  12. 23 Common MongoDB Query Operators & How to Use Them
  13. MongoDB GeoLocation Query Examples
  14. Introduction to MongoDB Transactions
  15. MongoDB Indexes: Top Index Types & How to Manage Them
  16. Top MongoDB Commands You Need to Know
  17. MongoDB Replication: A Complete Introduction
  18. How to Setup a MongoDB Cluster
  19. MongoDB Sharding: Concepts, Examples & Tutorials
  20. MongoDB Atlas: Setting Up & Using Managed MongoDB
  21. How To Run MongoDB as a Docker Container
  22. MongoDB Memory Usage, Management, & Requirements
  23. How To Use mongodump for MongoDB Backups
  24. Mongorestore Examples for Restoring MongoDB Backups
  25. How To Use PyMongo
  26. How to Use Mongoose for MongoDB & NodeJS
  27. MongoDB Cheat Sheet
  28. MongoDB vs Cassandra: NoSQL Databases Compared
  29. PostgreSQL vs MongoDB: Comparing Databases
  30. MySQL vs MongoDB: Comparing Databases
  31. MongoDB Certifications: An Introduction

These postings are my own and do not necessarily represent BMC's position, strategies, or opinion.

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