Introducing Dragonfly Cloud! Learn More

Question: How does MongoDB replication across data centers work?


MongoDB supports replication across data centers through its replica set architecture. A replica set is a group of MongoDB servers that maintain the same data set, providing redundancy and increasing data availability. For cross-data center replication, members of a replica set can be distributed across different physical locations.


To configure MongoDB for replication across data centers, follow these general steps:

  1. Deploy MongoDB Instances: Deploy instances of MongoDB across the data centers you wish to replicate data between.
  2. Configure the Replica Set: Configure these instances into a replica set by setting the replSetName parameter in the MongoDB configuration file or via the command line.
  3. Initiate the Replica Set: Connect to one of the instances and initiate the replica set with an initiation document that includes the hosts of all replica set members.
rs.initiate({ _id: 'myReplicaSet', members: [ { _id: 0, host: '' }, { _id: 1, host: '' }, { _id: 2, host: '', arbiterOnly: true } ] });

In this example, instances are located in three different data centers, with one acting as an arbiter. Arbiters do not store data but participate in elections for primary.


  • Latency: Network latency between data centers can impact replication lag and the time it takes for operations on the primary to be reflected on secondaries.
  • Read/Write Concerns: Adjust read and write concerns to ensure consistency and availability according to your application's requirements and tolerance for replication lag.
  • Arbiters: Use arbiters carefully. Having an arbiter in a third location can help avoid split-brain scenarios but doesn't contribute to fault tolerance in terms of data storage.

Disaster Recovery and High Availability

Cross-data center replication is crucial for disaster recovery and high availability. By distributing replica set members across geographically dispersed data centers, MongoDB can continue to operate even if a whole data center goes down.


Monitor replication lag and other performance metrics to ensure that the system operates within acceptable parameters. Tools like MongoDB Atlas offer built-in monitoring capabilities that can simplify this task.


MongoDB's replication across data centers is a powerful feature for building resilient, highly available applications. Proper configuration, alongside monitoring and maintenance, will help leverage the full potential of MongoDB's distributed data infrastructure.

Was this content helpful?

White Paper

Free System Design on AWS E-Book

Download this early release of O'Reilly's latest cloud infrastructure e-book: System Design on AWS.

Free System Design on AWS E-Book

Start building today 

Dragonfly is fully compatible with the Redis ecosystem and requires no code changes to implement.