MongoDB Replication

Introduction to MongoDB Replication

MongoDB replication provides redundancy and high availability through replica sets. This guide covers replica set configuration, management, and best practices for production deployments.

MongoDB Replication

MongoDB Replica Set Architecture

Replica Set Concepts

Replica Set Components

Primary Node

Handles all write operations and maintains the oplog

Secondary Nodes

Maintain copies of the primary's data and can serve read operations

Arbiter

Participates in elections but doesn't store data

Replication Process

  • Initial sync
  • Oplog replication
  • Heartbeat mechanism
  • Election process
  • Failover handling

Replica Set Configuration

Basic Setup

# Initialize replica set
rs.initiate({
    _id: "rs0",
    members: [
        { _id: 0, host: "mongodb1:27017" },
        { _id: 1, host: "mongodb2:27017" },
        { _id: 2, host: "mongodb3:27017" }
    ]
})

# Check replica set status
rs.status()

# Add new member
rs.add("mongodb4:27017")

# Remove member
rs.remove("mongodb4:27017")

Advanced Configuration

  • Priority settings
  • Hidden members
  • Delayed members
  • Arbiter configuration
  • Vote configuration

High Availability

Failover Process

Automatic Failover

Automatic election of new primary when current primary fails

Recovery Process

Automatic recovery and resynchronization of failed nodes

Data Consistency

Ensures data consistency across replica set members

Read Operations

  • Read preferences
  • Read concern levels
  • Load balancing
  • Latency optimization
  • Consistency requirements

Monitoring & Maintenance

Health Checks

# Check replica set status
rs.status()

# Check replication lag
db.printSlaveReplicationInfo()

# Check oplog status
db.getReplicationInfo()

# Monitor replication metrics
db.serverStatus().repl

Maintenance Tasks

  • Adding/removing members
  • Reconfiguring replica sets
  • Upgrading replica sets
  • Backup and restore
  • Performance tuning

Best Practices

Configuration Guidelines

  • Odd number of voting members
  • Geographic distribution
  • Network considerations
  • Hardware requirements
  • Security configuration

Common Pitfalls

  • Insufficient members
  • Poor network configuration
  • Inadequate monitoring
  • Missing security measures
  • Improper maintenance

Next Steps

Now that you understand MongoDB replication, you can explore:

MongoDB Tutorial