As Microsoft embraces a modern, modular .NET ecosystem, Azure Functions continues to evolve alongside it. The late 2024 update brings .NET 9 support to Azure Functions using the Isolated Worker model, allowing developers to build faster, more scalable, and more flexible serverless applications.

Let’s explore why this update is a big leap forward in cloud-native development on Azure.

🧱 What Is the Isolated Worker Model?

Traditionally, Azure Functions used an in-process model tightly coupled with the Azure runtime. While easy to start, this coupling made advanced customization harder.

The Isolated Worker model, introduced in .NET 5 and matured through .NET 6–8, fully separates:

• The Azure Functions host runtime

• From your application logic

Now, with .NET 9, you can take full advantage of a modern out-of-process architecture with the latest language features.

🚀 What’s New with .NET 9 Support

✅ 1. Latest Language Features

With .NET 9, you get:

• C# 13 support (e.g., primary constructors, collection expressions)

• New APIs for performance-critical code

• Extended support for AI workloads, memory management, and HTTP/JSON handling

This makes Azure Functions ideal for building modern APIs, backend services, and intelligent agents.

⚙️ 2. Improved Dependency Injection & Middleware

The Isolated Worker model continues to leverage ASP.NET Core-style DI, letting you:

• Register custom services

• Inject configuration, logging, telemetry, etc.

• Add middleware logic (e.g., authentication, validation) before the function is invoked

With .NET 9, these pipelines are more efficient and feature-rich—especially for microservice-oriented applications.

⚡ 3. Performance Gains

.NET 9 includes compiler-level enhancements and runtime improvements, leading to:

• Faster cold starts

• Lower memory usage

• Better handling of parallel invocations

Paired with Azure Functions’ dynamic scaling model, this means your apps now respond faster and consume fewer resources.

🔐 4. Enhanced Observability and Tracing

With .NET 9 support:

• Functions apps gain richer OpenTelemetry support

• You can export traces directly to Azure Monitor, Application Insights, or 3rd-party platforms

• Full support for custom log scopes and correlation IDs across requests

This makes debugging, tracing, and SLA reporting much easier.

🛠️ Migration & Getting Started

You can upgrade your Azure Functions app to .NET 9 by:

bash

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func init MyDotNet9App --worker-runtime dotnetIsolated --target-framework net9.0

Make sure:

• Your csproj references .NET 9 SDK

• Your host.json uses the "IsolatedWorker" version aligned with the latest Azure Functions host

Then deploy using:

bash

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az functionapp publish <YourAppName>

Note: .NET 9 is currently in Preview and will reach GA (General Availability) alongside official Azure Functions host support in H1 2025.

💡 Why It Matters

Here’s how the .NET 9 Isolated Worker support empowers developers:

Whether you’re building internal APIs or public-facing serverless microservices, this update makes Azure Functions a first-class platform for high-performance, future-ready apps.

🏁 Final Thoughts

.NET 9 in Azure Functions (Isolated Worker) is more than just a version upgrade—it’s a developer experience overhaul.

You now have:

• Cleaner architecture

• Richer language features

• More control over hosting and execution

This is a must-try for developers aiming to build modern, maintainable, and lightning-fast apps on Azure.