Microsoft Azure Functions problems and troubleshooting

When porting parts of elmah.io 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 read our series about Functions, please consider doing that.

Time 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: https://devblogs.microsoft.com/dotnet/visual-studio-tools-for-azure-functions/. 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:

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:

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: https://github.com/Azure/azure-functions-core-tools/issues/79

How can I use C# instead of scripts?

Since writing these posts, we have switched to using C# instead of C# scripts. While dynamic scripting is definitely cool, having your functions in a static language offers benefits like compile time errors and the possibility to reference other projects. Check out Precompilted functions for details.

My service bus input trigger stops consuming messages

We've experienced numerous problems keeping a function with an Azure Service bus input trigger alive. While it is a hack for sure, adding a timed function to all of your function apps, triggering an empty job every 5 minutes, fixes the issue.

function.json:

{
  "disabled": false,
  "bindings": [
    {
      "name": "myTimer",
      "type": "timerTrigger",
      "direction": "in",
      "schedule": "0 */5 * * * *"
    }
  ]
}

run.csx:

using Microsoft.Azure.WebJobs;

public static void Run(TimerInfo myTimer)
{
}

When adding two timed function to the same function app, only one of them is triggered

Could probably be caused by a lot of issues like wrong configuration etc. In my case, I had the configuration just right, but found a "feature" in Azure Functions. If adding two timed functions with the same class name and the same schedule, Azure executes one of the two functions twice. Changing the class name in one of the functions fixes the issue.

Everything around my function (execution, Kudu etc.) seems to run extremely slow. What's wrong?

Hard to say. But here's a thing to check. Functions need storage in order to place its files, execute functions etc. It's very important that the storage account assigned the Function is located in the same region as the Function app. We had a Function deployed to Europe, running on top of a storage account located in United States. Let's just say that it were running slowly and that the solution were hard to find. Microsoft promised to limit the options in the storage dropdown to only show storage accounts in the same region. But for now, make sure to select the right region when creating new Function apps.

How to monitor Azure Functions

The built-in monitoring solution for Azure Functions, still lack a lot to be really usable. Microsoft is currently working to integrate Functions into Application Insights. Check out our post Monitoring Azure Functions with the Portal and elmah.io for details about the possibilities and how to monitor your Functions with elmah.io.

How to get started with Functions

To get started writing functions, the wizard on the Azure Portal helps you getting started. You will quickly have to turn to some kind of documentation, but creating basic tasks is actually pretty intuitive through Portal. In order to utilize the many features of Functions, it's important to understand the flow of writing serverless code. Check out our blog series as well as the official documentation for Azure Functions to get started.

How to schedule using Cron expressions

You may have already noticed those funny-looking expressions in scheduled functions looking similar to this: 0 */5 * * * *. Those are Cron expressions which can be a bit hard to write and understand at first. Especially since most of the examples you will end up with from Google are using 5 identifiers and not 6. To help you understand and write these expressions, we have developed a free tool that we use when needing to write Cron expressions: Cron expression parser and creator tool.