Keyed Services in .NET 8 Dependency Injection — Azure Functions Example (C#)

An Azure Functions v4 demo on .NET 8 that demonstrates keyed dependency injection (AddKeyedScoped / [FromKeyedServices]) in the isolated worker model. Three HTTP endpoints each receive a different implementation of the same INotification interface, selected by its registered key — a way to choose between email, SMS, and push strategies without writing a factory class.

Overview

.NET 8 introduced first-class keyed service registration in the DI container. This project shows how to register multiple implementations of the same interface under different string keys and inject the correct one into each Azure Function using the [FromKeyedServices("key")] attribute.

Functions

Function	HTTP Method	Key	Notification Type
`emailnotificationfunction`	GET	`"email"`	`EmailNotification`
`pushnotificationfunction`	GET	`"push"`	`PushNotification`
`smsnotificationfunction`	GET	`"sms"`	`SmsNotification`

Each function calls INotification.NotifyAsync(message) on its injected implementation and returns a plain-text response confirming which channel was used.

DI Registration

services.AddKeyedScoped<INotification, EmailNotification>("email");
services.AddKeyedScoped<INotification, PushNotification>("push");
services.AddKeyedScoped<INotification, SmsNotification>("sms");

Injection in Functions

public class EmailNotificationFunction(
    [FromKeyedServices("email")] INotification notification,
    ILogger<EmailNotificationFunction> logger)

Requirements

.NET 8 SDK
Azure Functions Core Tools v4
A local.settings.json file in the project root (not committed to source control)

Minimum `local.settings.json`

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated",
    "APPLICATIONINSIGHTS_CONNECTION_STRING": ""
  }
}

NuGet Packages

Package	Version
`Microsoft.Azure.Functions.Worker`	1.20.1
`Microsoft.Azure.Functions.Worker.Extensions.Http`	3.1.0
`Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore`	1.2.0
`Microsoft.Azure.Functions.Worker.Sdk`	1.16.4
`Microsoft.ApplicationInsights.WorkerService`	2.21.0
`Microsoft.Azure.Functions.Worker.ApplicationInsights`	1.1.0

Running Locally

cd KeyedService
func start --port 7194

Usage

# Email notification
curl http://localhost:7194/api/emailnotificationfunction

# Push notification
curl http://localhost:7194/api/pushnotificationfunction

# SMS notification
curl http://localhost:7194/api/smsnotificationfunction

Each returns a plain-text confirmation such as notification sent [EMAIL].

The EmailNotification, PushNotification, and SmsNotification implementations only log the message (they await Task.CompletedTask); replace them with real email, push, or SMS providers in your own application.

Project Structure

KeyedService/
├── Functions/
│   ├── EmailNotificationFunction.cs   # Injects INotification keyed "email"
│   ├── PushNotificationFunction.cs    # Injects INotification keyed "push"
│   └── SmsNotificationFunction.cs     # Injects INotification keyed "sms"
├── Logic/
│   ├── Contract/
│   │   └── INotification.cs           # Interface: NotifyAsync(string message)
│   └── Manager/
│       ├── EmailNotification.cs       # Email implementation
│       ├── PushNotification.cs        # Push implementation
│       └── SmsNotification.cs         # SMS implementation
├── Properties/
│   └── launchSettings.json            # Default port: 7194
├── Program.cs                         # Host builder with keyed DI registration
├── host.json
└── KeyedService.csproj

FAQ

What are keyed services in .NET? Introduced in .NET 8, keyed services let you register several implementations of one interface under different keys (AddKeyedScoped, AddKeyedSingleton, AddKeyedTransient) and request a specific one with [FromKeyedServices("key")] or GetRequiredKeyedService<T>("key").

Do keyed services work in Azure Functions? Yes — this project uses them in the .NET 8 isolated worker model with constructor injection into function classes.

Documentation links

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