Dependency injection using Azure WebJobs SDK?

Question

The problem is that the Azure WebJobs SDK supports only public static methods as job entry-points which means there is no way of implementing constructor/property injection.

I am unable to find anything about this topic in official WebJobs SDK documentation/resources. The only solution that I came across is based on service locator (anti) pattern described on this post here.

Is there a good way to use "proper" dependency injection for projects based on Azure WebJobs SDK?

Answer 1

Azure WebJobs SDK now supports instance methods. Combining this with a custom IJobActivator allows you to use DI.

First, create the custom IJobActivator that can resolve a job type using your favourite DI container:

public class MyActivator : IJobActivator
{
    private readonly IUnityContainer _container;

    public MyActivator(IUnityContainer container)
    {
        _container = container;
    }

    public T CreateInstance<T>()
    {
        return _container.Resolve<T>();
    }
}

You need to register this class using a custom JobHostConfiguration:

var config = new JobHostConfiguration
{
    JobActivator = new MyActivator(myContainer)
};
var host = new JobHost(config);

Then, you can use a simple class with instance methods for your jobs (here I'm using Unity's constructor injection feature):

public class MyFunctions
{
    private readonly ISomeDependency _dependency;

    public MyFunctions(ISomeDependency dependency)
    {
        _dependency = dependency;
    }

    public Task DoStuffAsync([QueueTrigger("queue")] string message)
    {
        Console.WriteLine("Injected dependency: {0}", _dependency);

        return Task.FromResult(true);
    }
}

Answer 2

This is how I handled scoping using the new SDK. Using the IJobactivator as described by Alexander Molenkamp.

public class ScopedMessagingProvider : MessagingProvider
{
    private readonly ServiceBusConfiguration _config;
    private readonly Container _container;

    public ScopedMessagingProvider(ServiceBusConfiguration config, Container container)
        : base(config)
    {
        _config = config;
        _container = container;
    }

    public override MessageProcessor CreateMessageProcessor(string entityPath)
    {
        return new CustomMessageProcessor(_config.MessageOptions, _container);
    }

    private class CustomMessageProcessor : MessageProcessor
    {
        private readonly Container _container;

        public CustomMessageProcessor(OnMessageOptions messageOptions, Container container)
            : base(messageOptions)
        {
            _container = container;
        }

        public override Task<bool> BeginProcessingMessageAsync(BrokeredMessage message, CancellationToken cancellationToken)
        {
            _container.BeginExecutionContextScope();
            return base.BeginProcessingMessageAsync(message, cancellationToken);

        }

        public override Task CompleteProcessingMessageAsync(BrokeredMessage message, FunctionResult result, CancellationToken cancellationToken)
        {
            var scope = _container.GetCurrentExecutionContextScope();
            if (scope != null)
            {
                scope.Dispose();
            }

            return base.CompleteProcessingMessageAsync(message, result, cancellationToken);
        }
    }
}

You can the use your custom MessagingProvider in your JobHostConfiguration like

var serviceBusConfig = new ServiceBusConfiguration
{ 
    ConnectionString = config.ServiceBusConnectionString
};
serviceBusConfig.MessagingProvider = new ScopedMessagingProvider(serviceBusConfig, container);
jobHostConfig.UseServiceBus(serviceBusConfig);

Answer 3

After asking my own question about how to handle scoping ... I've just came up to this solution: I don't think this is ideal but I couldn't find any other solution for the moment.

In my example I am dealing with ServiceBusTrigger.

As I am using SimpleInjector, the implementation of the IJobActivator interface looks like that:

public class SimpleInjectorJobActivator : IJobActivator
{
    private readonly Container _container;

    public SimpleInjectorJobActivator(Container container)
    {
        _container = container;
    }

    public T CreateInstance<T>()
    {
        return (T)_container.GetInstance(typeof(T));
    }
}

Here, I am dealing with Triggered webjobs.

So I have two dependencies:

• A singleton:

  public interface ISingletonDependency { }
  
  public class SingletonDependency : ISingletonDependency { }
  

• And another that need to live only the time my function is triggered:

  public class ScopedDependency : IScopedDependency, IDisposable
  {
      public void Dispose()
      {
           //Dispose what need to be disposed...
      }
  }
  

So in order to have a process that run independently from the webjob. I've encapsulated my process into a class :

public interface IBrokeredMessageProcessor
{
    Task ProcessAsync(BrokeredMessage incommingMessage, CancellationToken token);
}

public class BrokeredMessageProcessor : IBrokeredMessageProcessor
{
    private readonly ISingletonDependency _singletonDependency;
    private readonly IScopedDependency _scopedDependency;

    public BrokeredMessageProcessor(ISingletonDependency singletonDependency, IScopedDependency scopedDependency)
    {
        _singletonDependency = singletonDependency;
        _scopedDependency = scopedDependency;
    }

    public async Task ProcessAsync(BrokeredMessage incommingMessage, CancellationToken token)
    {
        ...
    }
}

So now when the webjob starts, I need to register my dependencies depending their scopes:

class Program
{
    private static void Main()
    {
        var container = new Container();
        container.Options.DefaultScopedLifestyle = new ExecutionContextScopeLifestyle();
        container.RegisterSingleton<ISingletonDependency, SingletonDependency>();
        container.Register<IScopedDependency, ScopedDependency>(Lifestyle.Scoped);
        container.Register<IBrokeredMessageProcessor, BrokeredMessageProcessor>(Lifestyle.Scoped);
        container.Verify();

        var config = new JobHostConfiguration
        {
            JobActivator = new SimpleInjectorJobActivator(container)
        };

        var servicebusConfig = new ServiceBusConfiguration
        {
            ConnectionString = CloudConfigurationManager.GetSetting("MyServiceBusConnectionString")
        };

        config.UseServiceBus(servicebusConfig);
        var host = new JobHost(config);
        host.RunAndBlock();
    }
}

And this is the triggered job:

• Only have one dependency : the IoC container. Because this class is part of my composition root, it should be ok.

• It handle the scope into the triggered function.

  public class TriggeredJob
  {
      private readonly Container _container;
  
      public TriggeredJob(Container container)
      {
          _container = container;
      }
  
      public async Task TriggeredFunction([ServiceBusTrigger("queueName")] BrokeredMessage message, CancellationToken token)
      {
          using (var scope = _container.BeginExecutionContextScope())
          {
              var processor = _container.GetInstance<IBrokeredMessageProcessor>();
              await processor.ProcessAsync(message, token);
          }
      }
  }
  

Answer 4

All answers to the question are outdated now. Using the latest packages you can easily get constructor injection right out of the box. Two steps are only required:

1. Create the event handler function as an instance method in a non-static class. Let's call the class QueueFunctions.

2. Add your class to the list of services.

    builder.ConfigureServices(services =>
    {
        // Add 
        // dependencies
        // here
   
        services.AddScoped<QueueFunctions>();
    });
   

Now, you'll be able to inject dependencies through the constructor.

Answer 5

I've used a couple patterns that rely on the concept of child containers/scopes (depending on the terminology of your IoC container of choice). Not sure which ones support it, but I can tell you that StructureMap 2.6.x and AutoFac do.

The idea is to spin up a child scope for each message coming in, inject any context that's unique to that request, resolve the top-level object from the child scope, and then run your process.

Here's some generalized code showing it with AutoFac. It does do a direct resolve from the container, similar to the anti-pattern you're attempting to avoid, but it's been isolated to one place.

In this case, it's using a ServiceBusTrigger to fire the job, but could be anything - a job host could potentially have a list of these for the different queues/processes.

public static void ServiceBusRequestHandler([ServiceBusTrigger("queuename")] ServiceBusRequest request)
{
   ProcessMessage(request);
}

This method is called by all instances of the above methods. It wraps creation of the child scope in a using block to make sure things are cleaned up. Then, any objects that would vary per request and contain context used by other dependencies (user/client information, etc) would be created and injected into the child container (in this example, the IRequestContext). Finally, the component doing the work would be resolved from the child container.

private static void ProcessMessage<T>(T request) where T : IServiceBusRequest
{
    try
    {
        using (var childScope = _container.BeginLifetimeScope())
        {
            // create and inject things that hold the "context" of the message - user ids, etc

            var builder = new ContainerBuilder();
            builder.Register(c => new ServiceRequestContext(request.UserId)).As<IRequestContext>().InstancePerLifetimeScope();
            builder.Update(childScope.ComponentRegistry);

            // resolve the component doing the work from the child container explicitly, so all of its dependencies follow

            var thing = childScope.Resolve<ThingThatDoesStuff>();
            thing.Do(request);
        }
    }
    catch (Exception ex)
    {

    }
}