I’ve recently been working with Azure Isolated Functions for .Net 6. This is a kind of getting started guide – especially if you’re coming across from non-isolated.

What’s an Isolated Function

As is explained here, an isolated function is a function that runs out of process and self-hosted. Previously, there were issues with dependency conflicts because you were married to the function host.

What’s the Difference Between an Isolated an Non-Isolated Function?

A non-isolated function can have just one file in the project; for example:

And in that file, you can have a single method, decorated with a Function attribute:

        [FunctionName("Function1")]
        public async Task<HttpResponseData> Run(. . .

However, for an Isolated Function, you’ll need a Program.cs, with something along the lines of the following as a minimum:

        public static async Task Main(string[] args)
        {
            var host = new HostBuilder()
                .ConfigureFunctionsWorkerDefaults()
                .Build();

            await host.RunAsync();
        }

Further, the dependency libraries change; Isolated Functions use the following libraries (these obviously depend slightly on your bindings, but are a good start):

  <PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Abstractions" Version="1.1.0" />	 
  <PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="1.3.0" />
  <PackageReference Include="Microsoft.Azure.Functions.Worker" Version="1.6.0" />
  <PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Http" Version="3.0.13" />

Finally, you’ll need to change your decorator to:

[Function("Function1")]

From:

[FunctionName("Function1")]

FunctionName uses the old WebJobs namespace.

Some possible errors…

At least one binding must be declared.

This error typically happens in the following scenario: the method has a [Function] decorator, but within the method signature, there are no valid Bindings – that is, nothing that the Azure Function ecosystem understands. For example; the following signature would give that error:

[Function("Function1")]
public void MyFunc()
{
}

Specified condition “$(SelfContained)” evaluates to “” instead of a boolean.

For this, you need to specify the output type to be an executable:

<PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <AzureFunctionsVersion>v4</AzureFunctionsVersion>
    <OutputType>Exe</OutputType>
    <Nullable>enable</Nullable>
</PropertyGroup>