Azure Functions runtime versions overview

Azure Functions currently supports two versions of the runtime host. The following table details the currently supported runtime versions, their support level, and when they should be used:

This article details some of the differences between supported versions, how you can create each version, and how to change the version on which your functions run.

Levels of support

Levels of support

There are two levels of support:

• Generally available (GA) - Fully supported and approved for production use.
• Preview - Not yet supported, but expected to reach GA status in the future.

Languages

All functions in a function app must share the same language. You choose the language of functions in your function app when you create the app. The language of your function app is maintained in the FUNCTIONS_WORKER_RUNTIME setting, and can't be changed when there are existing functions.

¹ Reached the end of life (EOL) on December 13, 2022. We highly recommend you migrating your apps to version 4.x for full support.
² Supported through transpiling to JavaScript.

See the language-specific developer guide article for more details about supported language versions.
For information about planned changes to language support, see Azure roadmap.

For information about the language versions of previously supported versions of the Functions runtime, see Retired runtime versions.

Run on a specific version

The version of the Functions runtime used by published apps in Azure is dictated by the FUNCTIONS_EXTENSION_VERSION application setting. In some cases and for certain languages, other settings can apply.

By default, function apps created in the Azure portal, by the Azure CLI, or from Visual Studio tools are set to version 4.x. You can modify this version if needed. You can only downgrade the runtime version to 1.x after you create your function app but before you add any functions. Updating to a later major version is allowed even with apps that have existing functions.

Migrating existing function apps

When your app has existing functions, you must take precautions before moving to a later major runtime version. The following articles detail breaking changes between major versions, including language-specific breaking changes. They also provide you with step-by-step instructions for a successful migration of your existing function app.

• Migrate from runtime version 3.x to version 4.x
• Migrate from runtime version 1.x to version 4.x

Changing version of apps in Azure

The following major runtime version values are used:

Pinning to a specific minor version

To resolve issues your function app could have when running on the latest major version, you have to temporarily pin your app to a specific minor version. Pinning gives you time to get your app running correctly on the latest major version. The way that you pin to a minor version differs between Windows and Linux. To learn more, see How to target Azure Functions runtime versions.

Older minor versions are periodically removed from Functions. For the latest news about Azure Functions releases, including the removal of specific older minor versions, monitor Azure App Service announcements.

Minimum extension versions

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

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

Retired versions

These versions of the Functions runtime reached the end of extended support on December 13, 2022.

As soon as possible, you should migrate your apps to version 4.x to obtain full support. For a complete set of language-specific migration instructions, see Migrate apps to Azure Functions version 4.x.

Apps using versions 2.x and 3.x can still be created and deployed from your CI/CD DevOps pipeline, and all existing apps continue to run without breaking changes. However, your apps aren't eligible for new features, security patches, and performance optimizations. You can only get related service support after you upgrade your apps to version 4.x.

End of support for versions 2.x and 3.x is due to the end of support for .NET Core 3.1, which they had as a core dependency. This requirement affects all languages supported by Azure Functions.

Locally developed application versions

You can make the following updates to function apps to locally change the targeted versions.

Visual Studio runtime versions

In Visual Studio, you select the runtime version when you create a project. Azure Functions tools for Visual Studio supports the two major runtime versions. The correct version is used when debugging and publishing based on project settings. The version settings are defined in the .csproj file in the following properties:

<TargetFramework>net8.0</TargetFramework>
<AzureFunctionsVersion>v4</AzureFunctionsVersion>

<TargetFramework>net48</TargetFramework>
<AzureFunctionsVersion>v1</AzureFunctionsVersion>

Visual Studio Code and Azure Functions Core Tools

Azure Functions Core Tools is used for command-line development and also by the Azure Functions extension for Visual Studio Code. For more information, see Install the Azure Functions Core Tools.

For Visual Studio Code development, you could also need to update the user setting for the azureFunctions.projectRuntime to match the version of the tools installed. This setting also updates the templates and languages used during function app creation.

Bindings

Starting with version 2.x, the runtime uses a new binding extensibility model that offers these advantages:

• Support for third-party binding extensions.

• Decoupling of runtime and bindings. This change allows binding extensions to be versioned and released independently. You can, for example, opt to upgrade to a version of an extension that relies on a newer version of an underlying SDK.

• A lighter execution environment, where only the bindings in use are known and loaded by the runtime.

Except for HTTP and timer triggers, all bindings must be explicitly added to the function app project, or registered in the portal. For more information, see Register binding extensions.

The following table shows which bindings are supported in each runtime version.

This table shows the bindings that are supported in the major versions of the Azure Functions runtime:

¹ Starting with the version 2.x runtime, all bindings except HTTP and Timer must be registered. See Register binding extensions.

² Triggers aren't supported in the Consumption plan. Requires runtime-driven triggers.

³ Supported only in Kubernetes, IoT Edge, and other self-hosted modes only.

Function app timeout duration

The timeout duration for functions in a function app is defined by the functionTimeout property in the host.json project file. This property applies specifically to function executions. After the trigger starts function execution, the function needs to return/respond within the timeout duration. For more information, see Improve Azure Functions performance and reliability.

The following table shows the default and maximum values (in minutes) for specific plans:

¹ Regardless of the function app timeout setting, 230 seconds is the maximum amount of time that an HTTP triggered function can take to respond to a request. This is because of the default idle timeout of Azure Load Balancer. For longer processing times, consider using the Durable Functions async pattern or defer the actual work and return an immediate response.
² The default timeout for version 1.x of the Functions runtime is unlimited.

Next steps

For more information, see the following resources:

• Code and test Azure Functions locally
• How to target Azure Functions runtime versions
• Release notes