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Atlas Global Clusters require that you define single or multi-region Zones, where each zone supports write and read operations from geographically local shards. You can also configure zones that support global low-latency secondary reads. To learn more, see Global Writes Zones.
Atlas does not auto-configure or auto-shard collections. You can shard global collections for global writes. To use Global Writes, sharded collections must meet specific compatibility requirements. To learn more, see Global Cluster Sharding Reference.
Each Atlas global cluster supports up to nine 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.
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.
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.
Region where Atlas deploys the 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.
Region where Atlas deploys the non-electable secondary replica set members for supporting secondary read operations.
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.
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.
Atlas supports up to 50 shards per sharded cluster regardless of the number of zones. If you have requirements for more shards in your Global Cluster, click Support from the Atlas UI to contact support.
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. To learn more about creating a Global Cluster, see Create a Global Cluster.
If you are using the standard connection string format rather than the DNS seedlist format, removing an entire zone from an existing global cluster may result in a new connection string.
To verify the correct connection string after deploying the changes:
Click Databases in the top-left corner of Atlas.
Click Connect from the Database Deployments view.