Integrate with generic host (IHost interface) in asp.net core 2.1

[chuanboz]

asp.net core is refactor with generic host in aspnet/Hosting#1163 that has better support on DI and lifecycle management etc, but I do not see an integration for the ServiceFabric-AspnetCore.

the ask is to provide a ServiceFabricHost that implement IHost interface, to wrap the generic logic to register service type and also creating service instance.

here are specific difference for Service Fabric that deserve its own ServiceFabricHost:

1. different dependency scope of service instance level.

• Host scope (Singleton)
  -- Service instance scope (* unique for Service Fabric)
  ---Request scope
  ----Transient scope

2. different execution and lifecycle for IHostedService.
   for regular console host, the IHostedService shall be started right after host start; but for Service Fabric, it shall be registered with service factory and won't start the IHostedService directly; All IHostedService will be started as part of ICommunicationListener.OpenAsync; and IHostedService could be started multiple times within the same process, each time whenever there is a new service instance created.

here are sample scenario usage:

public static class ServiceFabricHostBuilderExtension
    {
        public static IHostBuilder UseServiceFabricHost(this IHostBuilder hostBuilder, string ServiceTypeName);

        public static IHostBuilder ConfigureWebHost(this IHostBuilder hostBuilder, Action<HostBuilderContext, IWebHostBuilder> configureWebHost);
    }

/// <summary>
        /// This is the entry point of the service host process.
        /// </summary>
        private static void Main()
        {
            var builder = new HostBuilder();

            // required, register service factory with ServiceFabricHost
            builder.UseServiceFabricHost("TestHttpServiceType");

            // config WebHost
            builder.ConfigureWebHost((context, webHostBuilder) => // the same native Startup experience from WebHost
                    webHostBuilder
                    .UseKestrel() // config to use Kestrel or HttpSys
                    .UseStartup<Startup>() // further extension with standard asp.net core Startup extension.
                );

            // optional, standard DI injection, injection here will be used in both host and service instance
            builder.ConfigureServices(sc => { });
            builder.ConfigureAppConfiguration(sc => { }); // configuration that will be applied to service instance.
            builder.ConfigureLogging(loggingBuilder => { }); // optional to config additional logging.

            // required, run the service until cancelled or aborted
            builder.Build().Run();
        }

[amanbha]

• @vturecek for feature request review, @chuanboz Could you also share more details for this feature request on how it would tie with SF and what scenarios you want to use it for, feel free to share a sample code demonstrating this?

[chuanboz]

I will use this feature in Microsoft Intune which builds on top of Service Fabric + Asp.net Core. Within Intune we have many Microservice teams and one common infra team, I want to leverage the flexible extensions support provided by the generic host and hook it up with Service Fabric, so that each Microservice team register their custom logic follow the generic host extension point, while as common infra team we could control certain common function consistently.

I'm still working on get the 2 tied together, I will share some sample code to demonstrating this later this month.

[OlegKarasik]

@chuanboz Can you take a look at this project? Maybe it can be of any use.

[chuanboz]

thanks @OlegKarasik for the link of your implementation on the similar idea to link generic host and service fabric, glad to know that I'm not alone here.

I have implemented above already and is using it in Microsoft Intune, but after discussing with @amanbha and @vturecek from Service Fabric team, they are hesitate to take the contribution for this yet in favor of Service Fabric Mesh as the future. I could understand where they're from for that decision, since Service Fabric Mesh has a complete different app model, in fact with SF Mesh you could just use regular generic host and regular asp.net core directly.

Several of internal Microsoft members from different teams has also reached out to me directly asking about the reference implementation details. I need all of you help to vote for this idea to show enough support, hoping that someday we could publish this as a public reference implementation and with the spirit of open source and community support this could become matual over time.

[chuanboz]

and for reference, here is the core interface that I used to implement this to link generic host with service fabric by translate the host service provider to service replica service provider, rest of interface are just the public one from generic host or from service fabric.

public interface IServiceProviderAdapter
{
        /// <summary>
        /// translate the host service provider to service replica (partition for statefull service or instance for stateless service) service provider
        /// </summary>
        /// <param name="hostServiceProvider">the service provider from process host.</param>
        /// <param name="serviceContext">The service context used to create service replica.</param>
        /// <returns>the service provider used for service replica dependency resolution.</returns>
        IServiceProvider CreateReplicaServiceProvider(IServiceProvider hostServiceProvider, ServiceContext serviceContext);
}

[OlegKarasik]

@chuanboz Thanks for the great comment!

I didn't dive deep into Mesh but as far as I understand (and hope) it isn't a replacement for Service Fabric (because if I am not mistaken there is no way to create stateful services in Mesh). I think when we would have a first release of Mesh then Service Fabric team will have some time to take a look at what community did to integrate generic host and Service Fabric.

[johncrim]

This definitely still needs to be implemented - from https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/generic-host?view=aspnetcore-3.0 :

Starting in ASP.NET Core 3.0, Generic Host is recommended for both HTTP and non-HTTP workloads. An HTTP server implementation, if included, runs as an implementation of IHostedService. IHostedService is an interface that can be used for other workloads as well.

Note that IHostedService is very similar to ICommunicationListener.

While addressing this, I would also like to see separation between building the app (configuration, services, http pipeline) and creating listeners. For example, it should be easy to create both HTTP and HTTPS listeners using the same configuration, DI container, and HTTP pipeline. The current design of AspNetCoreCommunicationListener doesn't support this separation very well.

I'm willing to provide this as a contribution, if it would be considered.

[amanbha]

@johncrim Thanks for offering to contribute, sure, we would consider your contribution as long as tis not a breaking change. Please feel free to create a PR.

[chuanboz]

@johncrim , in your design to use IHostedService as ICommunicationListener, can you clarify the following:

1. does the service fabric host and asp.net core app share the same IServiceProvider or different, and how do you plan to handle the case of multiple service instances hosted on the same process?
2. does asp.net core app and service fabric host share the same lifetime, in other words if the app stopped does it also stop the host, or support the scenario of just stop current instance of app and create a new instance but still keep the host active?

I'm asking because we implemented this already with a different model as your above and want to check if we could possible converge over time and have one shared public supported experience eventually.

[OlegKarasik]

Hi @johncrim @amanbha,
I have worked on the project that does integration with generic host (I was mentioning it about a year ago in the comments above in discussion with @chuanboz).

Does it looks like something you are looking for? (You can check projects Wiki for more detailed information about all the features).