Configure High Availability and Workload Isolation
On this page
- Considerations
- Electable Nodes for High Availability
- Add Electable Nodes
- Remove Electable Nodes
- Change Electable Nodes to Read-Only Nodes
- Improve the Availability of a Cluster
- Change the Highest Priority Provider or Region
- Read-Only Nodes for Optimal Local Reads
- Add Read-Only Nodes
- Remove Read-Only Nodes
- Change Workload Purpose of Nodes
- Analytics Nodes for Workload Isolation
- Add Analytics Nodes
- Remove Analytics Nodes
You can create multi-cloud MongoDB deployments in Atlas using any combination of cloud providers: AWS, Azure, and Google Cloud.
You can set the nodes in your MongoDB deployment to use different:
- Cloud providers
- Geographic regions
- Workload priorities
- Replication configurations
Using these options allows you to improve the availability and workload balancing of your cluster.
To configure node-specific options for your cluster, toggle Multi-Cloud, Multi-Region & Workload Isolation (M10+ clusters) to On.
A cluster may be hosted in:
- Multiple regions within a single cloud provider.
- Multiple regions across multiple cloud providers.
As each cloud provider has its own set of regions, multi-cloud clusters are also multi-region clusters.
Considerations
- Atlas does not guarantee that host names remain consistent with
respect to node types during topology changes.ExampleIf you have a cluster named
foo123containing an analytics nodefoo123-shard-00-03-a1b2c.mongodb.net:27017, Atlas does not guarantee that specific host name will continue to refer to an analytics node after a topology change, such as scaling a cluster to modify its number of nodes or regions. In sharded clusters, Atlas distributes the three config server nodes based on the number of electable regions in the cluster. If the cluster has:
- Only one electable region, Atlas deploys all three config nodes in that region.
- Two electable regions, Atlas deploys two config nodes in the highest priority region and one config node in the second highest priority region.
- Three or more electable regions, Atlas deploys one config node in each of the three highest priority regions.
- Having a large number of regions or having nodes spread across long distances may lead to long election times or replication lag.
- Clusters can span regions and cloud service providers. The total number
of nodes in clusters spanning across regions has a specific constraint
on a per-project basis.Atlas limits the total number of nodes in other regions in one
project to a total of 40. This total excludes:
- Google Cloud regions communicating with each other
- Free clusters or shared clusters
You can't create a multi-region cluster in a project if it has one or more clusters spanning 40 or more nodes in other regions.Contact Atlas support for questions or assistance with raising this limit.ExampleIf an Atlas project has nodes in clusters spread across three regions:- 30 nodes in Region A
- 10 nodes in Region B
- 5 nodes in Region C
- If you exclude Region C, Region A + Region B = 40.
- If you exclude Region B, Region A + Region C = 35, <= 40.
- If you exclude Region A, Region B + Region C = 15, <= 40.
Each combination of regions with the added 5 nodes still meets the per-project constraint:
- Region A + B = 40
- Region A + C = 40
- Region B + C = 20
- Atlas provides built-in custom write concerns for multi-region clusters. Use these write concerns to ensure your write operations propagate to a desired number of regions, thereby ensuring data consistency across your regions. To learn more, see Built-In Custom Write Concerns.
- The number of availability zones, zones, or fault domains in a region has no effect on the number of MongoDB nodes Atlas can deploy. MongoDB Atlas clusters are always made of replica sets with a minimum of three MongoDB nodes.
- If you use the standard connection string format
rather than the DNS seedlist format, removing an entire region from an
existing cross-region 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.
- If you plan on creating one or more VPC peering connections on
your first
M10+dedicated paid cluster for the selected region or regions, first review the documentation on VPC Peering Connections.
Electable Nodes for High Availability
If you add regions with electable nodes, you:
- increase data availability and
- reduce the impact of data center outages.
You may set different regions from one cloud provider or choose different cloud providers.
Atlas sets the node in the first row of the Electable nodes table as the Highest Priority region.
Atlas prioritizes nodes in this region for primary eligibility. Other nodes rank in the order that they appear. For more information, see Member Priority.
Each electable node can:
- Participate in replica set elections.
- Become the primary while the majority of nodes in the replica set remain available.
Add Electable Nodes
You can add electable nodes in one cloud provider and region from the Electable nodes for high availability section.
To add an electable node:
- Click Add a provider/region.
- Select the cloud provider from the Provider dropdown.
Select the region from the Region dropdown.
When you change the Provider option, the Region changes to a blank option. If you don't select a region, Atlas displays an error when you click Create Cluster.
Specify the desired number of Nodes for the provider and region.
The total number of electable nodes across all providers and regions in the cluster must equal 3, 5, or 7.
Atlas considers regions marked with a as recommended. These regions provide higher availability compared to other regions.
Remove Electable Nodes
To remove a node from a region, click the icon to the right side of that region. You cannot remove a node in the Highest Priority region.
Change Electable Nodes to Read-Only Nodes
You can change an electable node to a read-only node by adding a read-only node and removing an electable node at the same time. To learn more, see Change Workload Purpose of Nodes.
Improve the Availability of a Cluster
To improve the redundancy and availability of a cluster, increase the number of electable nodes in that region. Every Atlas cluster has a Highest Priority region. If your cluster spans multiple regions, you can select which cloud provider region should be the Highest Priority.
To prevent loss of availability and performance, consider the following scenarios:
Point of Failure | How to Prevent this Point of Failure |
|---|---|
Cloud Provider | Minimum of one node set in all three cloud providers. More than
one node per region. |
Region | Minimum of one node set in three or more different regions. More
than one node per region. |
Node |
|
Change the Highest Priority Provider or Region
If you change the Highest Priority provider and region in an active multi-region cluster, Atlas selects a new primary node in the provider and region that you specify (assuming that the number of nodes in each provider and region remains the same and nothing else is modified).
If you have an active 5-node cluster with the following configuration:
Nodes | Provider | Region | Priority |
|---|---|---|---|
3 | AWS | us-east-1 | Highest |
2 | Google Cloud | us-west3 |
To make the Google Cloud us-west3 nodes the Highest Priority, drag its row to the top of your cluster's Electable nodes list. After this change, Atlas elects a new PRIMARY in us-west3. Atlas doesn't start an initial sync or re-provision hosts when changing this configuration.
Certain circumstances may delay an election of a new primary.
A sharded cluster with heavy workloads on its primary shard may delay the election. This results in not having all primary nodes in the same region temporarily.
To minimize these risks, avoid modifying your primary region during periods of heavy workload.
Read-Only Nodes for Optimal Local Reads
Use read-only nodes to optimize local reads in the nodes' respective service areas.
Add Read-Only Nodes
You can add read-only nodes from the Read-Only Nodes for Optimal Local Reads section.
To add a read-only node in one cloud provider and region:
- Click Add a provider/region.
- Select the cloud provider from the Provider dropdown.
Select the region from the Region dropdown.
When you change the Provider option, the Region changes to a blank option. If you don't select a region, Atlas displays an error when you click Create Cluster.
- Specify the desired number of Nodes for the provider and region.
Atlas considers regions marked with a as recommended. These regions provide higher availability compared to other regions.
Read-only nodes don't provide high availability because they don't participate in elections. They can't become the primary for their cluster. Read-only nodes have distinct read preference tags that allow you to direct queries to desired regions.
Remove Read-Only Nodes
To remove all read-only nodes in one cloud provider and region, click the icon to the right of that cloud provider and region.
Change Workload Purpose of Nodes
You can change a node's workload purpose by adding and removing nodes at the same time.
You must add and remove the node within the same configuration change to reuse a node. If you remove the node, save the change, then add the node, Atlas provisions a new node instead.
For example, to change a read-only node to an electable node:
- Add an electable node.
- Remove a read-only node.
- Click Review Changes.
- Click Apply Changes.
Analytics Nodes for Workload Isolation
Use analytics nodes to isolate queries which you do not wish to contend with your operational workload. Analytics nodes help handle data analysis operations, such as reporting queries from BI Connector for Atlas. Analytics nodes have distinct replica set tags which allow you to direct queries to desired regions.
Click Add a region to select a region in which to deploy analytics nodes. Specify the desired number of Nodes for the region.
Add Analytics Nodes
You can add analytics nodes from the Analytics nodes for workload isolation section.
To add analytics nodes in one cloud provider and region:
- Click Add a provider/region.
- Select the cloud provider from the Provider dropdown.
Select the region from the Region dropdown.
When you change the Provider option, the Region changes to a blank option. If you don't select a region, Atlas displays an error when you click Create Cluster.
- Specify the desired number of Nodes for the provider and region.
Atlas considers regions marked with a as recommended. These regions provide higher availability compared to other regions.
Analytics nodes don't provide high availability because they don't participate in elections. They can't become the primary for their cluster.
Remove Analytics Nodes
To remove all analytics nodes in one cloud provider and region, click the icon to the right of that cloud provider and region.