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Migrate apps from Azure Functions version 3.x to version 4.x

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Azure Functions version 4.x is highly backwards compatible to version 3.x. Most apps should safely migrate to 4.x without requiring significant code changes. For more information about Functions runtime versions, see Azure Functions runtime versions overview.

Important

As of December 13, 2022, function apps running on versions 2.x and 3.x of the Azure Functions runtime have reached the end of extended support. For more information, see Retired versions.

This article walks you through the process of safely migrating your function app to run on version 4.x of the Functions runtime. Because project migration instructions are language dependent, make sure to choose your development language from the selector at the top of the article.

Identify function apps to migrate

Use the following PowerShell script to generate a list of function apps in your subscription that currently target versions 2.x or 3.x:

$Subscription = '<YOUR SUBSCRIPTION ID>' 
 
Set-AzContext -Subscription $Subscription | Out-Null

$FunctionApps = Get-AzFunctionApp

$AppInfo = @{}

foreach ($App in $FunctionApps)
{
     if ($App.ApplicationSettings["FUNCTIONS_EXTENSION_VERSION"] -like '*3*')
     {
          $AppInfo.Add($App.Name, $App.ApplicationSettings["FUNCTIONS_EXTENSION_VERSION"])
     }
}

$AppInfo

Choose your target .NET version

On version 3.x of the Functions runtime, your C# function app targets .NET Core 3.1 using the in-process model or .NET 5 using the isolated worker model.

When you migrate your function app, you have the opportunity to choose the target version of .NET. You can update your C# project to one of the following versions of .NET that are supported by Functions version 4.x:

.NET version .NET Official Support Policy release type Functions process model1,2
.NET 9 Preview3 Isolated worker model
.NET 8 LTS (end of support November 10, 2026) Isolated worker model,
In-process model2
.NET 6 LTS (end of support November 12, 2024) Isolated worker model,
In-process model2
.NET Framework 4.8 See policy Isolated worker model

1 The isolated worker model supports Long Term Support (LTS) and Standard Term Support (STS) versions of .NET, as well as .NET Framework. The in-process model only supports LTS releases of .NET, ending with .NET 8. For a full feature and functionality comparison between the two models, see Differences between in-process and isolate worker process .NET Azure Functions.

2 Support ends for the in-process model on November 10, 2026. For more information, see this support announcement. For continued full support, you should migrate your apps to the isolated worker model.

3 See Preview .NET versions in the isolated worker model for details on support, current restrictions, and instructions for using the preview version.

Tip

We recommend updating to .NET 8 on the isolated worker model. .NET 8 is the fully released version with the longest support window from .NET.

Although you can choose to instead use the in-process model, this is not recommended if it can be avoided. Support will end for the in-process model on November 10, 2026, so you'll need to move to the isolated worker model before then. Doing so while migrating to version 4.x will decrease the total effort required, and the isolated worker model will give your app additional benefits, including the ability to more easily target future versions of .NET. If you are moving to the isolated worker model, the .NET Upgrade Assistant can also handle many of the necessary code changes for you.

This guide doesn't present specific examples for .NET 6. If you need to target that version, you can adapt the .NET 8 examples.

Prepare for migration

If you haven't already, identify the list of apps that need to be migrated in your current Azure Subscription by using the Azure PowerShell.

Before you migrate an app to version 4.x of the Functions runtime, you should do the following tasks:

  1. Review the list of breaking changes between 3.x and 4.x.
  2. Complete the steps in Migrate your local project to migrate your local project to version 4.x.
  3. After migrating your project, fully test the app locally using version 4.x of the Azure Functions Core Tools.
  4. Run the pre-upgrade validator on the app hosted in Azure, and resolve any identified issues.
  5. Update your function app in Azure to the new version. If you need to minimize downtime, consider using a staging slot to test and verify your migrated app in Azure on the new runtime version. You can then deploy your app with the updated version settings to the production slot. For more information, see Update using slots.
  6. Publish your migrated project to the updated function app.

When you use Visual Studio to publish a version 4.x project to an existing function app at a lower version, you're prompted to let Visual Studio update the function app to version 4.x during deployment. This update uses the same process defined in Update without slots.

Migrate your local project

Upgrading instructions are language dependent. If you don't see your language, choose it from the selector at the top of the article.

Choose the tab that matches your target version of .NET and the desired process model (in-process or isolated worker process).

Tip

If you are moving to an LTS or STS version of .NET using the isolated worker model, the .NET Upgrade Assistant can be used to automatically make many of the changes mentioned in the following sections.

Project file

The following example is a .csproj project file that uses .NET Core 3.1 on version 3.x:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <AzureFunctionsVersion>v3</AzureFunctionsVersion>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="3.0.13" />
  </ItemGroup>
  <ItemGroup>
    <Reference Include="Microsoft.CSharp" />
  </ItemGroup>
  <ItemGroup>
    <None Update="host.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="local.settings.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <CopyToPublishDirectory>Never</CopyToPublishDirectory>
    </None>
  </ItemGroup>
</Project>

Use one of the following procedures to update this XML file to run in Functions version 4.x:

These steps assume a local C# project, and if your app is instead using C# script (.csx files), you should convert to the project model before continuing.

The following changes are required in the .csproj XML project file:

  1. Set the value of PropertyGroup.TargetFramework to net8.0.

  2. Set the value of PropertyGroup.AzureFunctionsVersion to v4.

  3. Add the following OutputType element to the PropertyGroup:

    <OutputType>Exe</OutputType>

  4. In the ItemGroup.PackageReference list, replace the package reference to Microsoft.NET.Sdk.Functions with the following references:

      <FrameworkReference Include="Microsoft.AspNetCore.App" />
  <PackageReference Include="Microsoft.Azure.Functions.Worker" Version="1.21.0" />
  <PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="1.17.2" />
  <PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore" Version="1.2.1" />
  <PackageReference Include="Microsoft.ApplicationInsights.WorkerService" Version="2.22.0" />
  <PackageReference Include="Microsoft.Azure.Functions.Worker.ApplicationInsights" Version="1.2.0" />

    Make note of any references to other packages in the Microsoft.Azure.WebJobs.* namespaces. You'll replace these packages in a later step.

  5. Add the following new ItemGroup:

    <ItemGroup>
  <Using Include="System.Threading.ExecutionContext" Alias="ExecutionContext"/>
</ItemGroup>

After you make these changes, your updated project should look like the following example:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <AzureFunctionsVersion>v4</AzureFunctionsVersion>
    <RootNamespace>My.Namespace</RootNamespace>
    <OutputType>Exe</OutputType>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
  <ItemGroup>
    <FrameworkReference Include="Microsoft.AspNetCore.App" />
    <PackageReference Include="Microsoft.Azure.Functions.Worker" Version="1.21.0" />
    <PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="1.17.2" />
    <PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore" Version="1.2.1" />
    <PackageReference Include="Microsoft.ApplicationInsights.WorkerService" Version="2.22.0" />
    <PackageReference Include="Microsoft.Azure.Functions.Worker.ApplicationInsights" Version="1.2.0" />
    <!-- Other packages may also be in this list -->
  </ItemGroup>
  <ItemGroup>
    <None Update="host.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="local.settings.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <CopyToPublishDirectory>Never</CopyToPublishDirectory>
    </None>
  </ItemGroup>
  <ItemGroup>
    <Using Include="System.Threading.ExecutionContext" Alias="ExecutionContext"/>
  </ItemGroup>
</Project>

Package and namespace changes

Based on the model you are migrating to, you might need to update or change the packages your application references. When you adopt the target packages, you then need to update the namespace of using statements and some types you reference. You can see the effect of these namespace changes on using statements in the HTTP trigger template examples later in this article.

If you haven't already, update your project to reference the latest stable versions of:

Depending on the triggers and bindings your app uses, your app might need to reference a different set of packages. The following table shows the replacements for some of the most commonly used extensions:

Scenario Changes to package references
Timer trigger Add
Microsoft.Azure.Functions.Worker.Extensions.Timer
Storage bindings Replace
Microsoft.Azure.WebJobs.Extensions.Storage
with
Microsoft.Azure.Functions.Worker.Extensions.Storage.Blobs,
Microsoft.Azure.Functions.Worker.Extensions.Storage.Queues, and
Microsoft.Azure.Functions.Worker.Extensions.Tables
Blob bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.Storage.Blobs
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.Storage.Blobs
Queue bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.Storage.Queues
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.Storage.Queues
Table bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.Tables
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.Tables
Cosmos DB bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.CosmosDB
and/or
Microsoft.Azure.WebJobs.Extensions.DocumentDB
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.CosmosDB
Service Bus bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.ServiceBus
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.ServiceBus
Event Hubs bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.EventHubs
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.EventHubs
Event Grid bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.EventGrid
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.EventGrid
SignalR Service bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.SignalRService
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.SignalRService
Durable Functions Replace references to
Microsoft.Azure.WebJobs.Extensions.DurableTask
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.DurableTask
Durable Functions
(SQL storage provider)		 Replace references to
Microsoft.DurableTask.SqlServer.AzureFunctions
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.DurableTask.SqlServer
Durable Functions
(Netherite storage provider)		 Replace references to
Microsoft.Azure.DurableTask.Netherite.AzureFunctions
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.DurableTask.Netherite
SendGrid bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.SendGrid
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.SendGrid
Kafka bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.Kafka
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.Kafka
RabbitMQ bindings Replace references to
Microsoft.Azure.WebJobs.Extensions.RabbitMQ
with the latest version of
Microsoft.Azure.Functions.Worker.Extensions.RabbitMQ
Dependency injection
and startup config		 Remove references to
Microsoft.Azure.Functions.Extensions
(The isolated worker model provides this functionality by default.)

See Supported bindings for a complete list of extensions to consider, and consult each extension's documentation for full installation instructions for the isolated process model. Be sure to install the latest stable version of any packages you are targeting.

Tip

Any changes to extension versions during this process might require you to update your host.json file as well. Be sure to read the documentation of each extension that you use. For example, the Service Bus extension has breaking changes in the structure between versions 4.x and 5.x. For more information, see Azure Service Bus bindings for Azure Functions.

Your isolated worker model application should not reference any packages in the Microsoft.Azure.WebJobs.* namespaces or Microsoft.Azure.Functions.Extensions. If you have any remaining references to these, they should be removed.

Tip

Your app might also depend on Azure SDK types, either as part of your triggers and bindings or as a standalone dependency. You should take this opportunity to update these as well. The latest versions of the Functions extensions work with the latest versions of the Azure SDK for .NET, almost all of the packages for which are the form Azure.*.

Program.cs file

When migrating to run in an isolated worker process, you must add the following program.cs file to your project:

using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

var host = new HostBuilder()
    .ConfigureFunctionsWebApplication()
    .ConfigureServices(services => {
        services.AddApplicationInsightsTelemetryWorkerService();
        services.ConfigureFunctionsApplicationInsights();
    })
    .Build();

host.Run();

This example includes ASP.NET Core integration to improve performance and provide a familiar programming model when your app uses HTTP triggers. If you do not intend to use HTTP triggers, you can replace the call to ConfigureFunctionsWebApplication with a call to ConfigureFunctionsWorkerDefaults. If you do so, you can remove the reference to Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore from your project file. However, for the best performance, even for functions with other trigger types, you should keep the FrameworkReference to ASP.NET Core.

The Program.cs file will replace any file that has the FunctionsStartup attribute, which is typically a Startup.cs file. In places where your FunctionsStartup code would reference IFunctionsHostBuilder.Services, you can instead add statements within the .ConfigureServices() method of the HostBuilder in your Program.cs. To learn more about working with Program.cs, see Start-up and configuration in the isolated worker model guide.

The default Program.cs examples above include setup of Application Insights integration for the isolated worker model. In your Program.cs, you must also configure any log filtering that should apply to logs coming from code in your project. In the isolated worker model, the host.json file only controls events emitted by the Functions host runtime. If you don't configure filtering rules in Program.cs, you may see differences in the log levels present for various categories in your telemetry.

Although you can register custom configuration sources as part of the HostBuilder, note that these similarly apply only to code in your project. Trigger and binding configuration is also needed by the platform, and this should be provided through the application settings, Key Vault references, or App Configuration references features.

Once you have moved everything from any existing FunctionsStartup to the Program.cs file, you can delete the FunctionsStartup attribute and the class it was applied to.

local.settings.json file

The local.settings.json file is only used when running locally. For information, see Local settings file.

When you migrate to version 4.x, make sure that your local.settings.json file has at least the following elements:

{
    "IsEncrypted": false,
    "Values": {
        "AzureWebJobsStorage": "AzureWebJobsStorageConnectionStringValue",
        "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"
    }
}

Note

When migrating from running in-process to running in an isolated worker process, you need to change the FUNCTIONS_WORKER_RUNTIME value to "dotnet-isolated".

host.json file

No changes are required to your host.json file. However, if your Application Insights configuration in this file from your in-process model project, you might want to make additional changes in your Program.cs file. The host.json file only controls logging from the Functions host runtime, and in the isolated worker model, some of these logs come from your application directly, giving you more control. See Managing log levels in the isolated worker model for details on how to filter these logs.

Class name changes

Some key classes changed names between versions. These changes are a result either of changes in .NET APIs or in differences between in-process and isolated worker process. The following table indicates key .NET classes used by Functions that could change when migrating:

.NET Core 3.1 .NET 5 .NET 8
FunctionName (attribute) Function (attribute) Function (attribute)
ILogger ILogger ILogger, ILogger<T>
HttpRequest HttpRequestData HttpRequestData, HttpRequest (using ASP.NET Core integration)
IActionResult HttpResponseData HttpResponseData, IActionResult (using ASP.NET Core integration)
FunctionsStartup (attribute) Uses Program.cs instead Uses Program.cs instead

There might also be class name differences in bindings. For more information, see the reference articles for the specific bindings.

Other code changes

This section highlights other code changes to consider as you work through the migration. These changes are not needed by all applications, but you should evaluate if any are relevant to your scenarios. Make sure to check Breaking changes between 3.x and 4.x for additional changes you might need to make to your project.

JSON serialization

By default, the isolated worker model uses System.Text.Json for JSON serialization. To customize serializer options or switch to JSON.NET (Newtonsoft.Json), see these instructions.

Application Insights log levels and filtering

Logs can be sent to Application Insights from both the Functions host runtime and code in your project. The host.json allows you to configure rules for host logging, but to control logs coming from your code, you'll need to configure filtering rules as part of your Program.cs. See Managing log levels in the isolated worker model for details on how to filter these logs.

HTTP trigger template

The differences between in-process and isolated worker process can be seen in HTTP triggered functions. The HTTP trigger template for version 3.x (in-process) looks like the following example:

using System;
using System.IO;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;

namespace Company.Function
{
    public static class HttpTriggerCSharp
    {
        [FunctionName("HttpTriggerCSharp")]
        public static async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.AuthLevelValue, "get", "post", Route = null)] HttpRequest req,
            ILogger log)
        {
            log.LogInformation("C# HTTP trigger function processed a request.");

            string name = req.Query["name"];

            string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
            dynamic data = JsonConvert.DeserializeObject(requestBody);
            name = name ?? data?.name;

            string responseMessage = string.IsNullOrEmpty(name)
                ? "This HTTP triggered function executed successfully. Pass a name in the query string or in the request body for a personalized response."
                : $"Hello, {name}. This HTTP triggered function executed successfully.";

            return new OkObjectResult(responseMessage);
        }
    }
}

The HTTP trigger template for the migrated version looks like the following example:

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.Logging;

namespace Company.Function
{
    public class HttpTriggerCSharp
    {
        private readonly ILogger<HttpTriggerCSharp> _logger;

        public HttpTriggerCSharp(ILogger<HttpTriggerCSharp> logger)
        {
            _logger = logger;
        }

        [Function("HttpTriggerCSharp")]
        public IActionResult Run(
            [HttpTrigger(AuthorizationLevel.Function, "get")] HttpRequest req)
        {
            _logger.LogInformation("C# HTTP trigger function processed a request.");

            return new OkObjectResult($"Welcome to Azure Functions, {req.Query["name"]}!");
        }
    }
}

To update your project to Azure Functions 4.x:

  1. Update your local installation of Azure Functions Core Tools to version 4.x.

  2. Update your app's Azure Functions extensions bundle to 2.x or above. For more information, see breaking changes.

  1. If needed, move to one of the Java versions supported on version 4.x.

  2. Update the app's POM.xml file to modify the FUNCTIONS_EXTENSION_VERSION setting to ~4, as in the following example:

    <configuration>
    <resourceGroup>${functionResourceGroup}</resourceGroup>
    <appName>${functionAppName}</appName>
    <region>${functionAppRegion}</region>
    <appSettings>
        <property>
            <name>WEBSITE_RUN_FROM_PACKAGE</name>
            <value>1</value>
        </property>
        <property>
            <name>FUNCTIONS_EXTENSION_VERSION</name>
            <value>~4</value>
        </property>
    </appSettings>
</configuration>
  1. If needed, move to one of the Node.js versions supported on version 4.x.
  1. Take this opportunity to upgrade to PowerShell 7.2, which is recommended. For more information, see PowerShell versions.
  1. If you're using Python 3.6, move to one of the supported versions.

Run the pre-upgrade validator

Azure Functions provides a pre-upgrade validator to help you identify potential issues when migrating your function app to 4.x. To run the pre-upgrade validator:

  1. In the Azure portal, navigate to your function app.

  2. Open the Diagnose and solve problems page.

  3. In Function App Diagnostics, start typing Functions 4.x Pre-Upgrade Validator and then choose it from the list.

  4. After validation completes, review the recommendations and address any issues in your app. If you need to make changes to your app, make sure to validate the changes against version 4.x of the Functions runtime, either locally using Azure Functions Core Tools v4 or by using a staging slot.

Update your function app in Azure

You need to update the runtime of the function app host in Azure to version 4.x before you publish your migrated project. The runtime version used by the Functions host is controlled by the FUNCTIONS_EXTENSION_VERSION application setting, but in some cases other settings must also be updated. Both code changes and changes to application settings require your function app to restart.

The easiest way is to update without slots and then republish your app project. You can also minimize the downtime in your app and simplify rollback by updating using slots.

Update without slots

The simplest way to update to v4.x is to set the FUNCTIONS_EXTENSION_VERSION application setting to ~4 on your function app in Azure. You must follow a different procedure on a site with slots.

az functionapp config appsettings set --settings FUNCTIONS_EXTENSION_VERSION=~4 -g <RESOURCE_GROUP_NAME> -n <APP_NAME>

You must also set another setting, which differs between Windows and Linux.

When running on Windows, you also need to enable .NET 6.0, which is required by version 4.x of the runtime.

az functionapp config set --net-framework-version v6.0 -g <RESOURCE_GROUP_NAME> -n <APP_NAME>

.NET 6 is required for function apps in any language running on Windows.

In this example, replace <APP_NAME> with the name of your function app and <RESOURCE_GROUP_NAME> with the name of the resource group.

You can now republish your app project that has been migrated to run on version 4.x.

Update using slots

Using deployment slots is a good way to update your function app to the v4.x runtime from a previous version. By using a staging slot, you can run your app on the new runtime version in the staging slot and switch to production after verification. Slots also provide a way to minimize downtime during the update. If you need to minimize downtime, follow the steps in Minimum downtime update.

After you've verified your app in the updated slot, you can swap the app and new version settings into production. This swap requires setting WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 in the production slot. How you add this setting affects the amount of downtime required for the update.

Standard update

If your slot-enabled function app can handle the downtime of a full restart, you can update the WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS setting directly in the production slot. Because changing this setting directly in the production slot causes a restart that impacts availability, consider doing this change at a time of reduced traffic. You can then swap in the updated version from the staging slot.

The Update-AzFunctionAppSetting PowerShell cmdlet doesn't currently support slots. You must use Azure CLI or the Azure portal.

  1. Use the following command to set WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 in the production slot:

    az functionapp config appsettings set --settings WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0  -g <RESOURCE_GROUP_NAME>  -n <APP_NAME>

    In this example, replace <APP_NAME> with the name of your function app and <RESOURCE_GROUP_NAME> with the name of the resource group. This command causes the app running in the production slot to restart.

  2. Use the following command to also set WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS in the staging slot:

    az functionapp config appsettings set --settings WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME>

  3. Use the following command to change FUNCTIONS_EXTENSION_VERSION and update the staging slot to the new runtime version:

    az functionapp config appsettings set --settings FUNCTIONS_EXTENSION_VERSION=~4 -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME>

  4. Version 4.x of the Functions runtime requires .NET 6 in Windows. On Linux, .NET apps must also update to .NET 6. Use the following command so that the runtime can run on .NET 6:

    When running on Windows, you also need to enable .NET 6.0, which is required by version 4.x of the runtime.

    az functionapp config set --net-framework-version v6.0 -g <RESOURCE_GROUP_NAME> -n <APP_NAME>

    .NET 6 is required for function apps in any language running on Windows.

    In this example, replace <APP_NAME> with the name of your function app and <RESOURCE_GROUP_NAME> with the name of the resource group.

  5. If your code project required any updates to run on version 4.x, deploy those updates to the staging slot now.

  6. Confirm that your function app runs correctly in the updated staging environment before swapping.

  7. Use the following command to swap the updated staging slot to production:

    az functionapp deployment slot swap -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME> --target-slot production

Minimum downtime update

To minimize the downtime in your production app, you can swap the WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS setting from the staging slot into production. After that, you can swap in the updated version from a prewarmed staging slot.

  1. Use the following command to set WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 in the staging slot:

    az functionapp config appsettings set --settings WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME>

  2. Use the following commands to swap the slot with the new setting into production, and at the same time restore the version setting in the staging slot.

    az functionapp deployment slot swap -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME> --target-slot production
az functionapp config appsettings set --settings FUNCTIONS_EXTENSION_VERSION=~3 -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME>

    You may see errors from the staging slot during the time between the swap and the runtime version being restored on staging. This error can happen because having WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 only in staging during a swap removes the FUNCTIONS_EXTENSION_VERSION setting in staging. Without the version setting, your slot is in a bad state. Updating the version in the staging slot right after the swap should put the slot back into a good state, and you call roll back your changes if needed. However, any rollback of the swap also requires you to directly remove WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 from production before the swap back to prevent the same errors in production seen in staging. This change in the production setting would then cause a restart.

  3. Use the following command to again set WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 in the staging slot:

    az functionapp config appsettings set --settings WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME>

    At this point, both slots have WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS=0 set.

  4. Use the following command to change FUNCTIONS_EXTENSION_VERSION and update the staging slot to the new runtime version:

    az functionapp config appsettings set --settings FUNCTIONS_EXTENSION_VERSION=~4 -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME>

  5. Version 4.x of the Functions runtime requires .NET 6 in Windows. On Linux, .NET apps must also update to .NET 6. Use the following command so that the runtime can run on .NET 6:

    When running on Windows, you also need to enable .NET 6.0, which is required by version 4.x of the runtime.

    az functionapp config set --net-framework-version v6.0 -g <RESOURCE_GROUP_NAME> -n <APP_NAME>

    .NET 6 is required for function apps in any language running on Windows.

    In this example, replace <APP_NAME> with the name of your function app and <RESOURCE_GROUP_NAME> with the name of the resource group.

  6. If your code project required any updates to run on version 4.x, deploy those updates to the staging slot now.

  7. Confirm that your function app runs correctly in the updated staging environment before swapping.

  8. Use the following command to swap the updated and prewarmed staging slot to production:

    az functionapp deployment slot swap -g <RESOURCE_GROUP_NAME>  -n <APP_NAME> --slot <SLOT_NAME> --target-slot production

Breaking changes between 3.x and 4.x

The following are key breaking changes to be aware of before upgrading a 3.x app to 4.x, including language-specific breaking changes. For a full list, see Azure Functions GitHub issues labeled Breaking Change: Approved.

If you don't see your programming language, go select it from the top of the page.

Runtime

  • Azure Functions Proxies is a legacy feature for versions 1.x through 3.x of the Azure Functions runtime. Support for Functions Proxies can be re-enabled in version 4.x so that you can successfully update your function apps to the latest runtime version. As soon as possible, you should instead switch to integrating your function apps with Azure API Management. API Management lets you take advantage of a more complete set of features for defining, securing, managing, and monetizing your Functions-based APIs. For more information, see API Management integration. To learn how to re-enable Proxies support in Functions version 4.x, see Re-enable Proxies in Functions v4.x.

  • Logging to Azure Storage using AzureWebJobsDashboard is no longer supported in 4.x. You should instead use Application Insights. (#1923)

  • Azure Functions 4.x now enforces minimum version requirements for extensions. Update to the latest version of affected extensions. For non-.NET languages, update to extension bundle version 2.x or later. (#1987)

  • Default and maximum timeouts are now enforced in 4.x for function apps running on Linux in a Consumption plan. (#1915)

  • Azure Functions 4.x uses Azure.Identity and Azure.Security.KeyVault.Secrets for the Key Vault provider and has deprecated the use of Microsoft.Azure.KeyVault. For more information about how to configure function app settings, see the Key Vault option in Manage key storage. (#2048)

  • Function apps that share storage accounts now fail to start when their host IDs are the same. For more information, see Host ID considerations. (#2049)

  • Azure Functions 4.x supports .NET 6 in-process and isolated apps.

  • InvalidHostServicesException is now a fatal error. (#2045)

  • EnableEnhancedScopes is enabled by default. (#1954)

  • Remove HttpClient as a registered service. (#1911)

  • Use single class loader in Java 11. (#1997)

  • Stop loading worker jars in Java 8. (#1991)

  • Node.js versions 10 and 12 aren't supported in Azure Functions 4.x. (#1999)

  • Output serialization in Node.js apps was updated to address previous inconsistencies. (#2007)

  • Default thread count has been updated. Functions that aren't thread-safe or have high memory usage could be impacted. (#1962)

  • Python 3.6 isn't supported in Azure Functions 4.x. (#1999)

  • Shared memory transfer is enabled by default. (#1973)

  • Default thread count has been updated. Functions that aren't thread-safe or have high memory usage could be impacted. (#1962)

Next steps

Learn more about Functions versions