Microsoft Azure Functions problems and troubleshooting

Thomas Ardal, April 6, 2017

When porting parts of to Functions, I've come across a long range of questions and WTF's. This post is a summary of these questions as well as the answered found while sweeping StackOverflow. If you haven't ready our series about Functions, please consider doing that:

This for some Q and A!

"Error 0x80070666: Cannot install a product when a newer version is installed" during installation of Visual Studio tooling

To get the tooling working, you will need a custom build of Microsoft Azure App Service Tools, based on the 2.9.6 codebase (available here: On one of my PC's, I already had App Service Tools 3.0.0 installed, which caused the error above. The solution were to uninstall 3.0.0 and install the custom 2.9.6 build.

Function templates missing in Visual Studio

Another instance of the error above. In my case, I thought that I had App Service Tools 2.9.6 installed, but in fact I had 3.0.0 installed. Restarting between uninstall of 3.0.0 and install 2.9.6 seemed to do wonders.

My Function isn't in the root directory, how to configure that?

I like the new structure in ASP.NET Core, with a solution in the root directory and a src folder containing one or more projects. As default, Azure Functions looks for functions in the root only. To configure a sub folder, click the Configure app settings button and add a new app setting named Project with the relative path of the folder containing the .funproj file:

Configure Project

Be aware not to specify the full path to the project file, as you'd do when configuring an ASP.NET MVC (and friends) application.

How do I override Function app settings?

All Functions in a Function App share a set of app settings, located in appsettings.json:

  "Values": {
    "AzureWebJobsStorage": "DefaultEndpointsProtocol=...",
    "AzureWebJobsDashboard": "DefaultEndpointsProtocol=...",
    "Connection": "Endpoint=..."

The Values object maps 1:1 to the values in the app settings section of the Function app settings. To override the Connection setting, simply input a new value in app settings:

Override Function app setting

How do I access a virtual machine through point-to-site VPN from a Function?

You can secure communications between a web app and a virtual machine using Azure Point-To-Site VPN, as described in my article on MSDN: Secure Communications Between Azure Web Apps and Virtual Machines. If you need the same feature from your function, the only solution I've found so far, is to select App Service Plan in Hosting Plan. Running the Function on the App Service Plan (rather than on the Consumption Plan), opens up for Networking settings in the Function app settings view.

Cannot start multiple Function hosts simultaneously

As default, Azure Functions tools (func.exe) starts a process listening on port 7071. When trying to start multiple Function hosts, the process will fail when an existing Function host is already running. To use different ports, use the --port setting:

func host start --port 7072

Something more clever may be build into func.exe. Follow this issue for details:

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