Deploy MongoDB – Replication – Sharding

April 2, 2014 Romain PIGNOLET ESN, 0

This page describe how to deploy MongoDB with Replication and Sharding.

Replication (Replica Set)

Create the necessary data directories for each member by issuing a command similar to the following:
```
  mkdir -p /srv/mongodb/rs0-0 /srv/mongodb/rs0-1 /srv/mongodb/rs0-2
```

Start your mongod instances in their own shell windows by issuing the following commands:

First member:

  mongod --port 27017 --dbpath /srv/mongodb/rs0-0 --replSet rs0 --smallfiles --oplogSize 128

Second member:

  mongod --port 27018 --dbpath /srv/mongodb/rs0-1 --replSet rs0 --smallfiles --oplogSize 128

Third member:

  mongod --port 27019 --dbpath /srv/mongodb/rs0-2 --replSet rs0 --smallfiles --oplogSize 128

The --smallfiles and --oplogSize settings reduce the disk space that each mongod instance uses. Use these options only for development !

Connect to one of your mongod instances through the mongo shell. You will need to indicate which instance by specifying its port number. For the sake of simplicity and clarity, you may want to choose the first one, as in the following command:
```
 mongo --port 27017
```
Use rs.initiate() to initiate the replica set.
In the mongo shell connected to the primary, add the second and third mongod instances to the replica set using the rs.add() method.
```
 rs.add("hostname:27018")
 rs.add("hostname:27019")
```

rs.status() return the replica set status.

rs.conf() return the replica set configuration.

Create data directories for each of the three config server instances.
```
mkdir /data/configdb
```
Start a config server instance. (In production deployments, you must deploy exactly three config server instances.)
```
mongod --configsvr --dbpath /data/configdb --port 27019
```

Start a mongos instance.

mongos --configdb config_server_hostnames

Example:

mongos --configdb cfg0.example.net:27019,cfg1.example.net:27019,cfg2.example.net:27019

Start all shards (each shard is a replica set).
Connect to mongos instance.
```
mongo --port 27017
```
Add each shard to the cluster using the sh.addShard() method.
```
sh.addShard( "rs0/mongodb0.example.net:27017" )
```
Specifying the name of the database for which to enable sharding.
```
sh.enableSharding("database")
```

sh.status() return the sharded cluster status.

For configure shard key, please read the official documentation.