Using the FunctionsStartup with Azure Functions


How to use the App startup on Azure Functions?

Azure Functions provide the FunctionsStartup as App startup. The FunctionsStartup is made up assembly attribute and class in Microsoft.Azure.Functions.Extensions.DependencyInjection namespace.

Let’s try to use it.


  • .NET Core v3.1
  • Azure Functions v3
  • Microsoft.NET.Sdk.Functions v3.0.3
  • Microsoft.Azure.Functions.Extensions v1.1.0
  • Visual Studio for Mac v8.10
    • Azure Functions Core Tools v3.0.3873
  • C# v8
  • macOS v11.6


Install Microsoft.Azure.Functions.Extensions package via NuGet.

Add Startup.cs , then you write the following code:

using Microsoft.Azure.Functions.Extensions.DependencyInjection;

[assembly: FunctionsStartup(typeof(YourNameSpace.Startup))]

namespace YourNameSpace
    public class Startup : FunctionsStartup
        public override void Configure(IFunctionsHostBuilder builder)

        public override void ConfigureAppConfiguration(IFunctionsConfigurationBuilder builder)

Run your Azure Functions project, you will get the below log:

Azure Functions Core Tools
Core Tools Version:       3.0.3873 Commit hash: c546cd456f0e58058cf6c37365eb5ccc5bb0840b  (64-bit)
Function Runtime Version:

[2021-10-21T05:34:42.388Z] Found /Path/to/your/azure-function-project.csproj. Using for user secrets file configuration.
[2021-10-21T05:34:43.475Z] Cannot create directory for shared memory usage: /dev/shm/AzureFunctions
[2021-10-21T05:34:43.475Z] System.IO.FileSystem: Access to the path '/dev/shm/AzureFunctions' is denied. Operation not permitted.


An error occurs if you use Microsoft.Azure.Functions.Extensions v1.1.0 and Azure Function Core Tools v3.0.2358. The log is below:

[10/21/2021 2:00:01 AM] A host error has occurred during startup operation 'a14dd57a-7186-436a-a012-1fbaec51c59f'.
[10/21/2021 2:00:01 AM] System.Private.CoreLib: Could not load type 'Microsoft.Azure.WebJobs.Hosting.IWebJobsStartup2' from assembly 'Microsoft.Azure.WebJobs.Host, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.

Workaround are following:

  • Workaround 1: Upgrade Azure Functions Core Tools to latest version
    • It just refresh the template for the Azure Functions when you click a refresh button in the “Configure your Azure Functions project” window which is displayed to create new Azure Functions with Visual Studio for Mac.
  • Workaround 2: Downgrade Microsoft.Azure.Functions.Extensions to v1.0.0

See more the information:

  • Could not load type ‘Microsoft.Azure.WebJobs.Hosting.IWebJobsStartup2’ · Issue #54 · Azure/azure-functions-dotnet-extensions · GitHub
  • References