Category: .NET

In my Running and Building Azure Functions with Modern .NET talk last week at the Mississauga .NET User Group, the session covered a handful of topics that I think every .NET developer building on Azure Functions should know about — upgrading to .NET 10, centralizing package management, and the new solution file format. This is the first in a short series of posts walking through each of those topics. Let’s start with .NET 10 support in Azure Functions and what’s new.

.NET 10 is Now Supported in Azure Functions

Azure Functions now supports .NET 10 on runtime version 4.x, and it’s a big deal for anyone who cares about building modern, long-lived serverless applications. .NET 10 support runs until November 14, 2028, so you’ve got a solid runway once you’re on it.

A few things to keep in mind before you start your upgrade:

• Only the isolated worker model supports .NET 10. The in-process model is not receiving a .NET 10 update and reaches end of support on November 10, 2026. If you haven’t started migrating off in-process, that date should be your motivation to get moving.
• .NET 10 runs on Functions 4.x across most hosting plans. The one exception is Linux Consumption, which will not receive .NET 10 support. If that’s your current plan, Flex Consumption is the migration target.
• The base container images have shifted from Debian to Ubuntu with .NET 10. If you have custom container builds, verify this against the official release notes before upgrading.

Minimum package versions required for .NET 10:

Make sure you’re on at least these versions or the runtime will not load correctly.

Before You Upgrade — Quick Checklist

• [ ] Confirm you’re on the isolated worker model (not in-process)
• [ ] Confirm your hosting plan supports .NET 10 (see above)
• [ ] Update Microsoft.Azure.Functions.Worker and Microsoft.Azure.Functions.Worker.Sdk to the minimum versions above
• [ ] If migrating from in-process: swap Microsoft.NET.Sdk.Functions for Microsoft.Azure.Functions.Worker.Sdk, and replace Microsoft.Azure.WebJobs.* packages with Microsoft.Azure.Functions.Worker.Extensions.* equivalents
• [ ] Verify your HTTP integration choice (see builder pattern section below)
• [ ] Test locally with Azure Functions Core Tools v4

The New FunctionsApplication Builder Pattern

The biggest developer-facing change in .NET 10 (and technically available since .NET 8 with certain configurations) is the switch to the FunctionsApplication.CreateBuilder pattern. If you’ve been building with the older HostBuilder approach, this will feel familiar but noticeably cleaner.

Here’s what the old pattern looked like:

var host = new HostBuilder()
    .ConfigureFunctionsWorkerDefaults()
    .ConfigureServices(services =>
    {
        services.AddSingleton<IMyService, MyService>();
    })
    .Build();
await host.RunAsync();

And here’s the new pattern:

var builder = FunctionsApplication.CreateBuilder(args);
builder.ConfigureFunctionsWebApplication();
builder.Services.AddSingleton<IMyService, MyService>();
await builder.Build().RunAsync();

Note: ConfigureFunctionsWebApplication() is for functions apps that use ASP.NET Core HTTP integration — it wires up the ASP.NET Core middleware pipeline. If your app is non-HTTP (queue triggers, timers, Service Bus, etc.) and you don’t need that integration, use ConfigureFunctionsWorkerDefaults() instead. Most starter templates will choose the right one, but it’s worth knowing what each does.

It’s a small surface area change but the intent is meaningful. Let me walk through why this matters.

Alignment with ASP.NET Core

ASP.NET Core has used WebApplication.CreateBuilder(args) since .NET 6. Azure Functions now mirrors this with FunctionsApplication.CreateBuilder(args). This consistency across .NET workloads is genuinely helpful — developers who work on both web APIs and Azure Functions no longer need to context-switch between two different initialization mental models.

Direct Access to the Services Collection

The old pattern required you to register services inside a ConfigureServices callback, which added an extra layer of nesting. With the new pattern, you access builder.Services directly — just like you would in an ASP.NET Core Program.cs. Cleaner, more readable, and easier to reason about.

Modern .NET Host Builder Infrastructure

Under the hood, the new pattern is built on HostApplicationBuilder, the modern hosting infrastructure introduced in .NET 6+. This brings with it better performance, improved configuration ordering, and enhanced hosting abstractions. It’s part of Microsoft’s broader effort to unify .NET across web apps, Azure Functions, Worker Services, and other application types — and honestly, it’s a move in the right direction.

I have a sample application over on my GitHub: calloncampbell/FunctionAppMigration at demo3-migrated-net10

What About Flex Consumption?

If you’re migrating off Linux Consumption — or just evaluating where to run modern Azure Functions — Flex Consumption is where the platform is headed and worth understanding alongside your .NET 10 upgrade.

Flex Consumption is a Linux-based hosting plan built on a new backend internally called Legion. It keeps the serverless pay-for-what-you-use billing model you’re used to, but it adds a lot more control:

• Scale to hundreds of instances in under a minute
• Up to 1,000 scale-out instances (note: scale-out instances and per-instance concurrency are separate concepts — you configure concurrency independently)
• Configurable per-instance concurrency
• VNET integration with scale-to-zero still supported
• Always-ready instances that reduce cold-start latency (optional; default is 0, so you pay only when you need them)
• Multiple memory size options
• Availability Zones support

If you’re building anything serious on Azure Functions right now, Flex Consumption paired with .NET 10 is where I’d be pointing you.

Summary

.NET 10 support in Azure Functions is a worthwhile upgrade. The migration from in-process to isolated worker model is no longer optional — with end of support coming November 2026 you need a plan. And once you’re on isolated worker with .NET 10, the new FunctionsApplication builder pattern makes initialization cleaner and more aligned with the rest of the .NET ecosystem. Pair that with a move to Flex Consumption and you’ve got a solid, modern foundation for your serverless workloads.

In the next posts in this series I’ll cover Central Package Management and the new SLNX solution file format — two more improvements that make the .NET developer experience noticeably better.

Enjoy!

References

• Azure Functions isolated worker model guide — Official docs for the isolated worker model
• What’s new in .NET 10 — Overview of .NET 10 features
• Migrate from in-process to isolated worker model — Step-by-step migration guide
• Azure Functions Flex Consumption GA announcement — General availability blog post
• Flex Consumption samples
• Try .NET 10 today — Download and get started