Define automatic failover policies for regional failure for Azure Cosmos DB for NoSQL

Automatic failover policies for regional failure in Azure Cosmos DB enable applications to maintain high availability and ensure continuous operation even in the event of a regional failure. With automatic failover policies, applications can seamlessly switch to a secondary region when the primary region becomes unavailable. This article will explain how to define automatic failover policies for regional failure in Azure Cosmos DB for NoSQL databases.

Azure Cosmos DB is a globally distributed, multi-model database service provided by Microsoft. It offers automatic distribution, horizontal scalability, and multiple consistency models to support various application requirements. Azure Cosmos DB provides multiple regional replicas to ensure high availability and durability. By leveraging the regional replicas, applications can continue to operate and serve data even if one or more regions experience an outage.

Steps to Define Automatic Failover Policies for Regional Failure

1. Create an Azure Cosmos DB account:

   Open the Azure portal (portal.azure.com) and search for “Azure Cosmos DB.” Click on “Azure Cosmos DB” from the search results and click the “Add” button to create a new account. Specify the required details such as account name, API, subscription, resource group, and preferred location.

2. Configure multiple write regions:

   After creating the Azure Cosmos DB account, navigate to the “Replicate data globally” section. Click on the “Add Region” button to select the additional regions where you want to replicate data. Choose the appropriate regions based on your application’s requirements and click the “Save” button to apply the changes.

3. Specify the failover priority:

   In the “Replicate data globally” section, you’ll see a list of the selected regions along with their priorities. Set the failover priority for each region by selecting the region and adjusting the priority using the up and down arrows. The priority determines the order of failover when the primary region becomes unavailable. Regions with a higher priority are selected first.

4. Enable automatic failover:

   In the “Automatic failover” section, toggle the switch to enable automatic failover for the account. Enabling automatic failover ensures that the secondary region(s) automatically take over when the primary region experiences a failure.

By following these steps, you have successfully defined automatic failover policies for regional failure in Azure Cosmos DB. Now, let’s see how the application can handle this failover seamlessly.

When using the Azure Cosmos DB .NET SDK in your application, you can specify the preferred locations for read and write operations. The SDK automatically routes the requests to the appropriate replica based on the specified policy. Here’s an example of how to configure the Cosmos DB client with preferred locations:

using Microsoft.Azure.Cosmos;

// Use the Cosmos DB client to perform read or write operations
Container container = cosmosClient.GetContainer("your-database", "your-container");
ItemResponse response = await container.ReadItemAsync(partitionKey, id, requestOptions);


In the above code snippet, the preferredLocations array specifies the preferred sequence of regions where the read or write requests should be routed. The Cosmos DB client will first attempt to use the primary region, and if it’s not available, it will automatically failover to the next preferred region based on the specified order.

By following these steps and leveraging the Cosmos DB SDK, you can ensure that your application continues to operate seamlessly even in the event of a regional failure. Azure Cosmos DB’s automatic failover policies allow you to design highly available NoSQL applications with minimal downtime.

It’s important to note that automatic failover may incur additional costs, as the secondary region(s) actively maintain the replicated data. Therefore, consider the costs and application requirements before enabling automatic failover for your Azure Cosmos DB account.

In conclusion, defining automatic failover policies for regional failure in Azure Cosmos DB is crucial for maintaining high availability and ensuring continuous operation of NoSQL applications. By configuring multiple write regions, specifying failover priorities, and enabling automatic failover, you can design resilient applications that seamlessly handle regional failures.