Azure Functions With .Net 5 - Execution On Isolated Process

Last year on November 10, 2020; .Net 5 was released. And Azure Functions, one of the biggest features for Azure, was left out of the release. It wasn't until March 10, 2021, that a new version was released to support .Net 5.

But with this new release, we found a new approach to the execution model. Here is where we now can see that Azure Functions are executed in an Isolated Process. But what is about this Isolated Process execution?

Since their inception the .Net and .Net Core function applications have run in the same host process, bringing with them unique advantages such as having a set of bindings and injections to the SDK. But on the other hand, the execution of functions for other languages is executed in an “out-of-process” model (outside the process) that allows executing the functionality in a separate process. That is, under the execution of a process that in turn is in charge of the execution of the functions.

And this is where the Azure Functions development and support team decides to adopt this model for .Net 5 support. Thus, if we want to work on this version, we will find a new way of working.

The first change that we are going to notice is that when we create a new project, let's say in Visual Studio, we will find the presence of the Program.cs class. Which is the entry point of the execution of the functions, that is, the process in charge of the execution.

Previously in Azure Functions for .Net Core 3.1, we could create a class that inherits from FunctionsStartup so that it is executed on launch. But in this aproach, we already have this functionality already in our projects.

Another change that we are going to find is that the base Nuget packages that we are going to use will be,

Microsoft.Azure.Functions.Worker
Microsoft.Azure.Functions.Worker.Sdk

and the link extension packages will be,

Microsoft.Azure.Functions.Worker.Extensions.*

Where * represents the trigger package (s) that we will be using in our functions. For instance,

Microsoft.Azure.Functions.Worker.Extensions.Http
Microsoft.Azure.Functions.Worker.Extensions.Timer

Here is a table with the changes or differences with Azure Functions for .Net 3.1

Feature/behavior	In-process (.NET Core 3.1)	Out-of-process (.NET 5.0)
.NET versions	LTS (.NET Core 3.1)	Current (.NET 5.0)
Core packages	Microsoft.NET.Sdk.Functions	Microsoft.Azure.Functions.Worker Microsoft.Azure.Functions.Worker.Sdk
Binding extension packages	Microsoft.Azure.WebJobs.Extensions.*	Under Microsoft.Azure.Functions.Worker.Extensions.*
Logging	ILogger passed to the function	ILogger obtained from FunctionContext
Cancellation tokens	Supported	Not supported
Output bindings	Out parameters	Return values
Output binding types	IAsyncCollector, DocumentClient, BrokeredMessage, and other client-specific types	Simple types, JSON serializable types, and arrays.
Multiple output bindings	Supported	Supported
HTTP trigger	HttpRequest/ObjectResult	HttpRequestData/HttpResponseData
Durable Functions	Supported	Not supported
Imperative bindings	Supported	Not supported
function.json artifact	Generated	Not generated
Configuration	host.json	host.json and custom initialization
Dependency injection	Supported	Supported
Middleware	Not supported	Supported
Cold start times	Typical	Longer, because of just-in-time start-up. Run on Linux instead of Windows to reduce potential delays.
ReadyToRun	Supported	TBD

** https://docs.microsoft.com/en-us/azure/azure-functions/dotnet-isolated-process-guide#differences-with-net-class-library-functions