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Global Write Zones and Zone Mapping

Each Atlas Global Cluster supports up to 9 distinct zones. Each zone consists of one Highest Priority region and one or more Electable, Read-only, or Analytics regions. The available regions depend on the selected cloud service provider.

Region Type Description
Highest Priority

Region where Atlas deploys the primary replica set member for the shard or shards associated with that zone. Clients can only issue write operations to the primary.

Atlas uses the geographic location of the Highest Priority regions to construct a map of geographically-near countries and subdivisions. The Global Writes cluster uses this map for directing write operations to the correct zone.

Tip

To facilitate low-latency local secondary reads of globally distributed data, for each zone in the cluster, add a Read-only node in the Highest Priority region of every other cluster zone.

Electable Region where Atlas deploys electable secondary replica set members for the shard or shards associated to that zone. Electable regions add additional fault tolerance in the event of a partial or total regional outage in the Highest Priority region.
Read-only Region where Atlas deploys non-electable secondary replica set members for supporting secondary read operations.
Analytics Region where Atlas deploys analytics nodes. Analytics nodes are read-only nodes configured with distinct replica set tags. You can use these tags to direct queries to specific regions. As a result, analytics nodes can help isolate reporting queries from your normal operational workload as well as reduce latency for local reads.

Shard Distribution

For each shard associated to a zone, Atlas distributes the shard nodes across the configured regions. While Atlas allows more than one shard per zone, users should instead consider creating additional zones to address high user volume in a concentrated geographic area.

Note

Atlas supports up to 50 shards per sharded cluster regardless of the number of zones. Contact support by clicking Support from the Atlas UI if you have requirements for more shards in your Global Cluster.

The Atlas cluster builder includes templates for automatically configuring Global Writes zones for the Global Cluster. Each template provides a visual description of the cluster zone configuration, including estimates of geographic latency and coverage. For complete documentation on creating a Global Cluster, see Configure a Global Cluster.

Considerations

If you are using the standard connection string format rather than the DNS, removing an entire zone from an existing global cluster may result in a new connection string. After deploying the changes verify the correct connection string by clicking Connect from the Clusters view.