MongoDB - Replication -Part I

I will be running Mongod instance in windows environment. I am planning to create one primary and 2 secondary instances.
First, I have created 3 folders in C:\
c:\MongoRepl\1
c:\MongoRepl\2
c:\MongoRepl\3

I will be using port no 27007 (primary) ,27008 ,27009. I have made sure these ports are allowed incoming/outgoing in firewall.

Now, I will create a standalone mongod instance first. Then, create a database on the instance.

mongod --dbpath c:\MongoRepl\1 --port 27007 --smallfiles --oplogSize 50

open another terminal and connect to Mongod shell and import replication database

mongo --port 27007 --shell replication.js

Now, Cloed the mongod shell. Restarted Mongod instance as a replica.

mongod --replSet Mya --dbpath c:\MongoRepl\1 --port 27007 --smallfiles --oplogSize 50

You will set EMPTYConfig error.

Next, we will start two other mongod instances (secondary), we will join them to replicaset Mya

mongod --replSet Mya --dbpath c:\MongoRepl\2 --port 27008 --smallfiles --oplogSize 50

mongod --replSet Mya --dbpath c:\MongoRepl\3 --port 27009 --smallfiles --oplogSize 50

Now, we will initiate a replica from mongo us initiate command.

rs.initiate()
rs.status()

create a configuration

cfg={
_id:"Mya",
members:[
{_id:0,host:"machinename:27007"},
{_id:1,host:"machinename:27008"},
{_id:2,host:"machinename:27009"},
]
}

Initiate Replica

rs.initiate(cfg)

Check replica status on primary 

rs.status()

Open termainal and start mongo

mongo --port 27008
mongo --port 27009

Read from secondary

I need to run rs.slaveOk() to read from secondary

rs.slaveOk()

Write to Primary

for(var i=0; i< 50000;i++){db.foo.insert({_id:i});sleep(i);}

While for statement is running, check on secondary rowcount

db.foo.count()

FailOver to Secondary

Run the command in Primary

rs.stepDown()

Now new primary is 27008

Now we will close Mongod instance on 27007.

rs.status()
27007 is unreachable since we shut down 27007

Reconfigure

On new primary replica. run config and rs.reconfig(cfg)

cfg={
_id:"Mya",
members:[
{_id:1,host:"machinename:27008"},
{_id:2,host:"machinename:27009"},
]
}

rs.reconfig(cfg)

Now, we have even number node.

Replica set information are stored in local db

use local
db.system.replset.find().pretty()