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.NET Isolated Worker Model

This guide explains the .NET isolated worker model for Azure Functions, including host startup, dependency injection, trigger attributes, bindings, and migration-safe coding patterns.

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Why isolated worker is the default

The isolated worker model runs your function code in a separate process from the Functions host. This gives clearer versioning boundaries, modern .NET hosting patterns, and easier dependency control.

flowchart TD
    A[Functions Host Runtime] --> B[gRPC worker channel]
    B --> C[.NET isolated worker process]
    C --> D[Function methods]

Host startup with Program.cs

Use a standard HostBuilder startup:

using Microsoft.Extensions.Hosting;

var host = new HostBuilder()
    .ConfigureFunctionsWebApplication()
    .Build();

host.Run();

HTTP trigger pattern

Use HttpRequestData and HttpResponseData with the trigger attribute:

using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;
using Microsoft.Extensions.Logging;
using System.Net;

public class HttpFunctions
{
    private readonly ILogger<HttpFunctions> _logger;

    public HttpFunctions(ILogger<HttpFunctions> logger)
    {
        _logger = logger;
    }

    [Function("GetStatus")]
    public HttpResponseData GetStatus(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = "status/{id?}")] HttpRequestData req)
    {
        _logger.LogInformation("Status endpoint called.");
        HttpResponseData response = req.CreateResponse(HttpStatusCode.OK);
        response.WriteString("{\"status\":\"ok\"}");
        return response;
    }
}

Trigger and binding examples

  • Queue input: [QueueTrigger("queue-name", Connection = "AzureWebJobsStorage")]
  • Blob input: [BlobTrigger("container/{name}", Connection = "AzureWebJobsStorage")]
  • Timer trigger: [TimerTrigger("0 */5 * * * *")]
  • Queue output: [QueueOutput("queue-name", Connection = "AzureWebJobsStorage")]
  • Blob output: [BlobOutput("container/{name}", Connection = "AzureWebJobsStorage")]
[Function("QueueCopy")]
[QueueOutput("processed-items", Connection = "AzureWebJobsStorage")]
public string Run(
    [QueueTrigger("incoming-items", Connection = "AzureWebJobsStorage")] string message)
{
    return $"processed: {message}";
}

Dependency injection and logging

Use constructor injection for ILogger<T> and services. Do not use in-process patterns such as context.GetLogger().

public class TimerFunctions
{
    private readonly ILogger<TimerFunctions> _logger;

    public TimerFunctions(ILogger<TimerFunctions> logger)
    {
        _logger = logger;
    }

    [Function("Heartbeat")]
    public void Heartbeat([TimerTrigger("0 */5 * * * *")] TimerInfo timer)
    {
        _logger.LogInformation("Heartbeat executed at {Timestamp}", DateTime.UtcNow);
    }
}

project-root/
├── Functions/
│   ├── HttpFunctions.cs
│   ├── TimerFunctions.cs
│   └── QueueFunctions.cs
├── Program.cs
├── host.json
├── local.settings.json
└── MyProject.csproj

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See Also

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