Azure Cosmos DB trigger and bindings for Azure Functions 2.x and higher overview

• Version 1
• Version 2 and higher

This set of articles explains how to work with Azure Cosmos DB bindings in Azure Functions 2.x and higher. Azure Functions supports trigger, input, and output bindings for Azure Cosmos DB.

Action	Type
Run a function when an Azure Cosmos DB document is created or modified	Trigger
Read an Azure Cosmos DB document	Input binding
Save changes to an Azure Cosmos DB document	Output binding

Note

This reference is for Azure Functions version 2.x and higher. For information about how to use these bindings in Functions 1.x, see Azure Cosmos DB bindings for Azure Functions 1.x.

This binding was originally named DocumentDB. In Azure Functions version 2.x and higher, the trigger, bindings, and package are all named Azure Cosmos DB.

Supported APIs

Azure Cosmos DB bindings are only supported for use with Azure Cosmos DB for NoSQL. Support for Azure Cosmos DB for Table is provided by using the Table storage bindings, starting with extension 5.x. For all other Azure Cosmos DB APIs, you should access the database from your function by using the static client for your API, including Azure Cosmos DB for MongoDB, Azure Cosmos DB for Cassandra, and Azure Cosmos DB for Apache Gremlin.

Install extension

The extension NuGet package you install depends on the C# mode you're using in your function app:

Isolated worker model

Functions execute in an isolated C# worker process. To learn more, see Guide for running C# Azure Functions in an isolated worker process.

In-process model

Important

Support will end for the in-process model on November 10, 2026. We highly recommend that you migrate your apps to the isolated worker model for full support.

Functions execute in the same process as the Functions host. To learn more, see Develop C# class library functions using Azure Functions.

In a variation of this model, Functions can be run using C# scripting, which is supported primarily for C# portal editing. To update existing binding extensions for C# script apps running in the portal without having to republish your function app, see Update your extensions.

The process for installing the extension varies depending on the extension version:

Extension 4.x+

This section describes using a class library. For C# scripting, you would need to instead install the extension bundle, version 4.x.

This version of the Azure Cosmos DB bindings extension introduces the ability to connect using an identity instead of a secret. For a tutorial on configuring your function apps with managed identities, see the creating a function app with identity-based connections tutorial.

This version also changes the types that you can bind to, replacing the types from the v2 SDK Microsoft.Azure.DocumentDB with newer types from the v3 SDK Microsoft.Azure.Cosmos. Learn more about how these new types are different and how to migrate to them from the SDK migration guide, trigger, input binding, and output binding examples.

This extension version is available as a NuGet package, version 4.x.

Functions 2.x+

This section describes using a class library. For C# scripting, you would need to instead install the extension bundle, version 2.x or 3.x.

Working with the trigger and bindings requires that you reference the appropriate NuGet package. Install the NuGet package, version 3.x.

Extension 4.x+

This version of the Azure Cosmos DB bindings extension introduces the ability to connect using an identity instead of a secret. For a tutorial on configuring your function apps with managed identities, see the creating a function app with identity-based connections tutorial.

Add the extension to your project by installing the NuGet package, version 4.x.

If you're writing your application using F#, you must also configure this extension as part of the app's startup configuration. In the call to ConfigureFunctionsWorkerDefaults() or ConfigureFunctionsWebApplication(), add a delegate that takes an IFunctionsWorkerApplication parameter. Then within the body of that delegate, call ConfigureCosmosDBExtension() on the object:

let hostBuilder = new HostBuilder()
hostBuilder.ConfigureFunctionsWorkerDefaults(fun (context: HostBuilderContext) (appBuilder: IFunctionsWorkerApplicationBuilder) ->
    appBuilder.ConfigureCosmosDBExtension() |> ignore
) |> ignore

Functions 2.x+

Add the extension to your project by installing the NuGet package, version 3.x.

Install bundle

The Azure Cosmos DB bindings extension is part of an extension bundle, which is specified in your host.json project file. You may need to modify this bundle to change the version of the binding, or if bundles aren't already installed. To learn more, see extension bundle.

Because of schema changes in the Azure Cosmos DB SDK, version 4.x of the Azure Cosmos DB extension requires azure-functions-java-library V3.0.0 for Java functions.

Bundle v4.x

This version of the bundle contains version 4.x of the Azure Cosmos DB bindings extension that introduces the ability to connect using an identity instead of a secret. For a tutorial on configuring your function apps with managed identities, see the creating a function app with identity-based connections tutorial.

You can add this version of the extension from the preview extension bundle v4 by adding or replacing the following code in your host.json file:

{
  "version": "2.0",
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle.Preview",
    "version": "[4.0.0, 5.0.0)"
  }
}

To learn more, see Update your extensions.

Bundle v2.x and v3.x

You can install this version of the extension in your function app by registering the extension bundle, version 2.x or 3.x.

{
    "version": "2.0",
    "extensionBundle": {
        "id": "Microsoft.Azure.Functions.ExtensionBundle",
        "version": "[3.3.0, 4.0.0)"
    }
}

Binding types

The binding types supported for .NET depend on both the extension version and C# execution mode, which can be one of the following:

Isolated worker model

An isolated worker process class library compiled C# function runs in a process isolated from the runtime.

In-process model

An in-process class library is a compiled C# function runs in the same process as the Functions runtime.

Choose a version to see binding type details for the mode and version.

Extension 4.x+

The Azure Cosmos DB extension supports parameter types according to the table below.

Binding scenario	Parameter types
Cosmos DB trigger (single document)	JSON serializable types1
Cosmos DB trigger (batch of documents)	IEnumerable<T>where T is a JSON serializable type1
Cosmos DB input (single document)	JSON serializable types1
Cosmos DB input (query returning multiple documents)	CosmosClient IEnumerable<T> where T is a JSON serializable type1
Cosmos DB output (single document)	JSON serializable types1
Cosmos DB output (multiple documents)	ICollector<T> or IAsyncCollector<T> where T is a JSON serializable type1

¹ Documents containing JSON data can be deserialized into known plain-old CLR object (POCO) types.

Functions 2.x+

Earlier versions of the extension exposed types from the now deprecated Microsoft.Azure.Documents namespace. Newer types from Microsoft.Azure.Cosmos are exclusive to extension 4.x and higher.

Extension 4.x+

The isolated worker process supports parameter types according to the tables below. Support for binding to types from Microsoft.Azure.Cosmosis in preview.

Cosmos DB trigger

When you want the function to process a single document, the Cosmos DB trigger can bind to the following types:

Type	Description
JSON serializable types	Functions tries to deserialize the JSON data of the document from the Cosmos DB change feed into a plain-old CLR object (POCO) type.

When you want the function to process a batch of documents, the Cosmos DB trigger can bind to the following types:

Type	Description
IEnumerable<T>where T is a JSON serializable type	An enumeration of entities included in the batch. Each entry represents one document from the Cosmos DB change feed.

Cosmos DB input binding

When you want the function to process a single document, the Cosmos DB input binding can bind to the following types:

Type	Description
JSON serializable types	Functions attempts to deserialize the JSON data of the document into a plain-old CLR object (POCO) type.

When you want the function to process multiple documents from a query, the Cosmos DB input binding can bind to the following types:

Type	Description
IEnumerable<T>where T is a JSON serializable type	An enumeration of entities returned by the query. Each entry represents one document.
CosmosClient1	A client connected to the Cosmos DB account.
Database1	A client connected to the Cosmos DB database.
Container1	A client connected to the Cosmos DB container.

¹ To use these types, you need to reference Microsoft.Azure.Functions.Worker.Extensions.CosmosDB 4.4.0 or later and the common dependencies for SDK type bindings.

Cosmos DB output binding

When you want the function to write to a single document, the Cosmos DB output binding can bind to the following types:

Type	Description
JSON serializable types	An object representing the JSON content of a document. Functions attempts to serialize a plain-old CLR object (POCO) type into JSON data.

When you want the function to write to multiple documents, the Cosmos DB output binding can bind to the following types:

Type	Description
T[] where T is JSON serializable type	An array containing multiple documents. Each entry represents one document.

For other output scenarios, create and use a CosmosClient with other types from Microsoft.Azure.Cosmos directly. See Register Azure clients for an example of using dependency injection to create a client type from the Azure SDK.

Functions 2.x+

Earlier versions of extensions in the isolated worker process only support binding to JSON serializable types. Additional options are available to extension 4.x and higher.

Exceptions and return codes

Binding	Reference
Azure Cosmos DB	HTTP status codes for Azure Cosmos DB

host.json settings

This section describes the configuration settings available for this binding in versions 2.x and higher. Settings in the host.json file apply to all functions in a function app instance. The example host.json file below contains only the version 2.x+ settings for this binding. For more information about function app configuration settings in versions 2.x and later versions, see host.json reference for Azure Functions.

Extension 4.x+

{
    "version": "2.0",
    "extensions": {
        "cosmosDB": {
            "connectionMode": "Gateway",
            "userAgentSuffix": "MyDesiredUserAgentStamp"
        }
    }
}

Property	Default	Description
connectionMode	Gateway	The connection mode used by the function when connecting to the Azure Cosmos DB service. Options are Direct and Gateway
userAgentSuffix	n/a	Adds the specified string value to all requests made by the trigger or binding to the service. This makes it easier for you to track the activity in Azure Monitor, based on a specific function app and filtering by User Agent.

Functions 2.x+

{
    "version": "2.0",
    "extensions": {
        "cosmosDB": {
            "connectionMode": "Gateway",
            "protocol": "Https",
            "leaseOptions": {
                "leasePrefix": "prefix1"
            }
        }
    }
}

Property	Default	Description
connectionMode	Gateway	The connection mode used by the function when connecting to the Azure Cosmos DB service. Options are Direct and Gateway
protocol	Https	The connection protocol used by the function when connection to the Azure Cosmos DB service. Read here for an explanation of both modes.
leasePrefix	n/a	Lease prefix to use across all functions in an app.

Next steps

• Run a function when an Azure Cosmos DB document is created or modified (Trigger)
• Read an Azure Cosmos DB document (Input binding)
• Save changes to an Azure Cosmos DB document (Output binding)