Azure Triggered Webjobs Scope for Dependency Injection

Question

I've read and asked some questions on how to use DI using WebJob and especially Triggered Webjobs.

• SimpleInjector - Azure WebJob with TimerTrigger - Register IDisposable
• Dependency injection using Azure WebJobs SDK?

I still try to figure out how to integrate gracefully DI in triggered webjobs and @Steven asked me a good question :

Isn't there a way to wrap the execution of your service in some scope? For instance, MVC and Web API have an IDependencyScope abstraction for this. This notifies the starting and ending of a request. To be able to do scoping, you either need to have such interception point or you need to be able to wrap the call to JobActivator.

I know that I can start a scope inside my triggered function but I would like to know if there are any point of extensibility in the sdk that allow us to do scoping ?

Thanks.

Answer 1

I've opened an request Add IDependencyScope to handle scoping to the Azure Webjob team.

I've create a small library to gather classes around Azure Webjobs and SimpleInjector :

• Nuget download
• GitHub project

For QueueTrigger and ServiceBustrigger, I've come accross these solutions :

• ServiceBusTrigger (from this answer: https://stackoverflow.com/a/33759649/4167200):

  public sealed 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 ScopedMessageProcessor(_config.MessageOptions, _container);
      }
  
      private class ScopedMessageProcessor : MessageProcessor
      {
          private readonly Container _container;
  
          public ScopedMessageProcessor(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)
          {
              _container.GetCurrentExecutionContextScope()?.Dispose();
              return base.CompleteProcessingMessageAsync(message, result, cancellationToken);
          }
      }
  }
  

  You can use your custom MessagingProvider in your JobHostConfiguration like

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

• QueueTrigger:

  public sealed class ScopedQueueProcessorFactory : IQueueProcessorFactory
  {
      private readonly Container _container;
  
      public ScopedQueueProcessorFactory(Container container)
      {
          _container = container;
      }
  
      public QueueProcessor Create(QueueProcessorFactoryContext context)
      {
          return new ScopedQueueProcessor(context, _container);
      }
  
      private class ScopedQueueProcessor : QueueProcessor
      {
          private readonly Container _container;
  
          public ScopedQueueProcessor(QueueProcessorFactoryContext context, Container container)
              : base(context)
          {
              _container = container;
          }
  
          public override Task<bool> BeginProcessingMessageAsync(CloudQueueMessage message, CancellationToken cancellationToken)
          {
              _container.BeginExecutionContextScope();
              return base.BeginProcessingMessageAsync(message, cancellationToken);
          }
  
          public override Task CompleteProcessingMessageAsync(CloudQueueMessage message, FunctionResult result,
              CancellationToken cancellationToken)
          {
              _container.GetCurrentExecutionContextScope()?.Dispose();
              return base.CompleteProcessingMessageAsync(message, result, cancellationToken);
          }
      }
  }
  

  You can use your custom IQueueProcessorFactory in your JobHostConfiguration like this:

   var config = new JobHostConfiguration();
   config.Queues.QueueProcessorFactory = new ScopedQueueProcessorFactory(container);