Implement client singleton

Completed

Each instance of the CosmosClient class has a few features that are already implemented on your behalf:

• Instances are already thread-safe
• Instances efficiently manage connections
• Instances cache addresses when operating in direct mode

Because of this behavior, each time you destroy and recreate and instance within a single .NET AppDomain, the new instances lose the benefits of the caching and connection management.

The Azure Cosmos DB for NoSQL SDK team recommends that you use a single instance per AppDomain for the lifetime of the application. This small change to your setup allows for better SDK client-side performance and more efficient connection management.

Tip

It's simple to use a singleton in a typical .NET console application. For ASP.NET web applications, you should review how to create a singleton instance using the dependency injection framework of your choice.

The CosmosClient in the Python SDK is lightweight, and the Azure Cosmos DB SDK for Python automatically handles connection management efficiently. However, for performance and resource efficiency, the recommendation is to reuse the same CosmosClient instance throughout your application.

• The Python SDK is thread-safe, so a single instance can be shared across multiple threads.
• Creating and disposing of multiple instances unnecessarily increases resource consumption.

Best Practices

• Create a single CosmosClient instance and reuse it throughout the lifetime of your application.
• In long-running applications, store the CosmosClient instance in a globally accessible location, such as a module-level variable or a dependency injection container.

Tip

If you're using a framework like FastAPI or Flask, consider creating the CosmosClient once during app startup and reusing it across requests.

The CosmosClient class in the JavaScript SDK is designed so it can be reused across operations.

• The JavaScript SDK manages connections efficiently, but frequent instantiation can still impact performance.
• CosmosClient isn't inherently expensive to create, but reusing a single instance helps optimize resource usage.

Best Practices

• Create a single CosmosClient instance and reuse it across your application.
• In a Node.js environment, initialize the CosmosClient once and share it across modules.
• If using a web framework like Express.js, initialize the CosmosClient during application startup and use it across requests.

Tip

In serverless environments like Azure Functions, consider using a static variable to persist the CosmosClient instance across function invocations.