MongoDB — Replication

What is Replication?

Replication provides redundancy and high availability.

Replica Set

• Primary node receives writes
• Secondary nodes replicate data
• Automatic failover

Initialize Replica Set

rs.initiate({
  _id: "rs0",
  members: [
    { _id: 0, host: "localhost:27017" },
    { _id: 1, host: "localhost:27018" },
    { _id: 2, host: "localhost:27019" }
  ]
})

Check Status

rs.status()

Add Member

rs.add("localhost:27018")

Remove Member

rs.remove("localhost:27018")

Mini Practice

1. Initialize replica set
2. Check status
3. Add a member
4. Test failover

Up Next

Continue with Sharding — horizontal scaling.