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Reconfigure a Replica Set During a Regional Outage

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  • Prerequisites
  • Procedure

During a regional outage, your cluster might not have a primary node if the regional outage affects a majority of the cluster's electable nodes. You can use the Atlas UI to restore your Atlas multi-region cluster by reconfiguring your cluster.

If you reconfigure your cluster during an outage, your cluster might lose data in the following circumstances:

  • If your MongoDB process didn't replicate write operations to the node that becomes primary after the reconfiguration in any cluster. Your replica set rolls back these writes when the unavailable members become available again. To learn more, see Rollbacks During Replica Set Failover.

  • In sharded clusters, if your MongoDB process didn't replicate chunk migrations. The data inconsistency might cause orphaned chunks.


If you force a reconfiguration for a sharded cluster, Atlas adds two new nodes to the config server replica set in a region unaffected by the outage. When you apply subsequent cluster changes after the sharded cluster becomes healthy, Atlas removes the additional nodes.

A regional outage or regional outage simulation that affects the highest priority regions in a sharded cluster could cause the cluster to become inoperable for read operations. To restore the config servers, do the following:

  • Configure a read preference that is suitable for querying secondary nodes for reads.

  • Reconfigure the cluster for regaining electable nodes.

Your cluster must be experiencing a total outage of nodes in one or more regions with at least one electable node remaining in another region. To learn how to simulate a regional outage for your multi-region cluster, see Simulate Regional Outage.

For assistance with other causes of node outages, contact support.

To restore your Atlas multi-region cluster from an outage, you must manually reconfigure your replica set:


Under Electable nodes for high availability, you can add new nodes to:

  • An existing region by editing the number of nodes in the Nodes column

  • A new region by clicking + Add a provider/region


We strongly advise not adding nodes to one of the regions with an outage.


Read the Considerations for force configuration, and check the box next to I have reviewed these considerations for force configuration and agree to proceed.

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