Central Cluster and Member Clusters

MongoDB recommends that you identify one cluster to act as a central cluster. The central cluster hosts the Kubernetes Operator and acts as the control plane for the multi-cluster deployment. This central cluster can also host replica set members. This documentation refers to other Kubernetes clusters that host replica set members as member clusters.

Communication between replica set members occurs over a service mesh, which means that your database doesn’t rely on the central cluster to function. Note that if the central cluster fails, you can’t use the Kubernetes Operator to change your deployment until access to this cluster is restored or until you redeploy the Kubernetes Operator to an available Kubernetes cluster.

You can host your application on any Kubernetes cluster in the service mesh. Your application can be co-located on a member cluster with one of the replica set nodes that you deployed using the Kubernetes Operator, or you can host your application on a cluster that doesn’t host replica set nodes or the Kubernetes Operator.

To learn more, see the Deployment Architecture and Diagram.