Create a MongoDB Replica Set

mongodb cluster replication centos ubuntu

Create 3 mongodb servers. Make sure update hosts files on all nodes or on DNS server

168.1.10 mongodb01
168.1.11 mongodb02
168.1.12 mongodb03

Generate a key file on mongodb01

openssl rand -base64 741 > keyfile
scp keyfile mongodb02:~/
scp keyfile mongodb03:~/

Do following commands on all servers

sudo mkdir /opt/mongodb
sudo mv ~/keyfile /opt/mongodb
sudo chmod 400 /opt/mongodb/keyfile

Update ownership on Ubuntu/Debian:

sudo chown mongodb:mongodb /opt/mongodb/keyfile

Update ownership on CentOS

sudo chown mongod:mongod /opt/mongodb/keyfile
sudo chcon system_u:object_r:mongod_var_lib_t:s0 /opt/mongodb/keyfile

Create an Administrator User (only on primary node: mongodb01)

mongo
use admin
db.createUser({user: "mongo-admin", pwd: "password", roles:[{role: "root", db: "admin"}]})

Configure MongoDB

Edit /etc/mongod.conf on all nodes. You can edit on one node and copy it to other nodes

net:
  port: 27017
#  bindIp: 127.0.0.1  # Listen to local interface only, comment to listen on all interfaces.

security:
  authorization: enabled
  keyFile: /opt/mongodb/mongo-keyfile

replication:
  replSetName: rs0

Restart mongodb on all nodes

sudo systemctl restart mongod

Initiate replication and add members on primary node mongodb01

mongo -u mongo-admin -p --authenticationDatabase admin
rs.initiate()
rs.add("mongodb02")
rs.add("mongodb03")

If primary node already has data, using following command to prevent secondary node vode. You can change the priority and votes values after database synced.

rs.add( { host: "mongodb02:27017", priority: 0, votes: 0 } )
rs.add( { host: "mongodb03:27017", priority: 0, votes: 0 } )

Check configuration and status

rs.conf()
rs.status()

Troubleshooting

If all slave nodes stuck at STARTUP status, check the host value of primary. You can update as below:

r0:PRIMARY> var cfg = rs.conf()
rs0:PRIMARY> cfg.members[0].host="mongodb01"
rs0:PRIMARY> rs.reconfig(cfg)

Source:

https://docs.mongodb.com/manual/core/replica-set-members/

https://docs.mongodb.com/manual/tutorial/deploy-replica-set/

https://linode.com/docs/databases/mongodb/create-a-mongodb-replica-set/

https://serverfault.com/questions/693282/mongo-secondaries-stuck-at-startup-state

Written on March 16, 2018