Failed Build in Visual Studio Team Services after Xamarin upgrade

This week I updated Visual Studio’s version of Xamarin. All was well until I kicked off a build for my Andriod project in Visual Studio Team Services (VSTS). During the Build Xamarin.Android Project step I recieved the following error and my build failed:

C:\Program Files (x86)\Java\jdk1.6.0_45\\bin\javac.exe -J-Dfile.encoding=UTF8 -d obj\Release\android\bin\classes -classpath ....
obj\Release\android\src\android\support\design\R.java:10: cannot access java.lang.Object
bad class file: java\lang\Object.class(java\lang:Object.class)
class file has wrong version 52.0, should be 50.0
Please remove or make sure it appears in the correct subdirectory of the classpath.
 public final class R {

The interesting part in the error message was the class file has wrong version 52.0, should be 50.0 message. This was ultimately what helped me find the error.

After a few minutes of searching, it was obvious that I had the wrong JDK version for building my assembly. Most of the issues were Android Studio specific but I found an issue were this happened in Visual Studio. This wasn’t Visual Studio, instead VSTS but it got me down the right path.

Fix - Setting the Build Version explicitly in Build.Andriod step

Now that I had some idea of what was going on, I headed over to my VSTS Build process and noticed that there was an option in the Build Xamarin.Android step to set the JDK Version. Looking at the output above I noticed I was using JDK 6. I tried JDK 7 and got the message Unsupported major.minor version 52.0. So I tried the only value left which was JDK 8 and it worked. Here is the screen shot of the updated setting:

update jdk version number in vsts

I assume that there is a good explanation for the change but I have not found it yet. Hope this helps!

ASP.NET Core cannot find runtime for Framework '.NETCoreApp'

Today I upgrade my ASP.NET Core application from version 1.0 to version 1.0.1 because of a bug in Entity Framework. Right after updating to the latest ASP.NET Core version, I built the project but ended up with the following error in Visual Studio:

Can not find runtime target for framework '.NETFramework,Version=v4.5.1' compatible with one of the target runtimes: 'win10-x64, win81-x64, win8-x64, win7-x64'. Possible causes:
The project has not been restored or restore failed - run dotnet restore
You may be trying to publish a library, which is not supported. Use dotnet pack to distribute libraries.

Fix - Update project.json

After searching around for a few minutes I found issue #2442 on GitHub. This the issue states that you need to update your project.json and you have two options:

(1). Include the platforms you want to build for explicitly:

"runtimes": {
    "win10-x64": {},
    "win8-x64": {} 
},

(2). Update the reference Microsoft.NETCore.App to include the type as platform:

"Microsoft.NETCore.App": {
    "version": "1.0.1",
    "type": "platform"
}

Conclusion

For more information on .NET Core Application Deployment you can read the docs. This is again another reason I love that all this work is being done out in the open. It really makes finding issues and bugs of this type easier. Hope that Helps!

Service Fabric ASP.NET Core could not load file or assembly ServiceFabricServiceModel

After adding a reference to retrieve a Service Fabric Actor to my ASP.NET Core Web API project I got the following error when making the call to create the actor using IMyActor actor = ActorProxy.Create<IMyActor>(actorId, serviceuri);:

System.IO.FileNotFoundException: Could not load file or assembly 'ServiceFabricServiceModel, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.
File name: 'ServiceFabricServiceModel, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
   at Microsoft.ServiceFabric.Services.Common.FabricServiceConfigSection.Initialize()
   at Microsoft.ServiceFabric.Services.Communication.FabricTransport.Common.FabricTransportSettings.LoadFrom(String sectionName, String filepath, String configPackageName)
   at Microsoft.ServiceFabric.Services.Communication.FabricTransport.Common.FabricTransportSettings.TryLoadFrom(String sectionName, FabricTransportSettings& settings, String filepath, String configPackageName)
   at Microsoft.ServiceFabric.Services.Communication.FabricTransport.Common.FabricTransportSettings.GetDefault(String sectionName)
   at Microsoft.ServiceFabric.Actors.Remoting.FabricTransport.FabricTransportActorRemotingProviderAttribute.CreateServiceRemotingClientFactory(IServiceRemotingCallbackClient callbackClient)
   at Microsoft.ServiceFabric.Actors.Client.ActorProxyFactory.CreateServiceRemotingClientFactory(Type actorInterfaceType)
   at Microsoft.ServiceFabric.Actors.Client.ActorProxyFactory.GetOrCreateServiceRemotingClientFactory(Type actorInterfaceType)
   at Microsoft.ServiceFabric.Actors.Client.ActorProxyFactory.CreateActorProxy[TActorInterface](Uri serviceUri, ActorId actorId, String listenerName)
   at Microsoft.ServiceFabric.Actors.Client.ActorProxy.Create[TActorInterface](ActorId actorId, Uri serviceUri, String listenerName)
   at Web.Controllers.Controller.<Create>d__1.MoveNext() in 

From this stackoverflow answer, it seems that there is currently an issue with the dotnet cli when working with nuget packages that do not explicitly reference assemblies. In this case, it is specifically an issue with Microsoft.ServiceFabric.Services package (version 2.0.217). When the ASP.NET Core publish action occurs, the ServiceFabricServiceModel.dll does not get copied to the publish folder but it is in the packages folder for the library.

Fixing with a postbuild script in project.json

This will likely be fixed but in the mean time you can fix this issue by adding a postbuild script in the ASP.NET Core RC2 project.json file. I used xcopy to copy the file from the packages folder to the publish directory. Once there, Service Fabric was able to package it up for deployment and everything worked.

In the project.json file add a scripts command:

{
  //...

  "scripts": {
     "postpublish": [ "xcopy ..\\packages\\Microsoft.ServiceFabric.Services.2.0.217\\lib\\net45\\ServiceFabricServiceModel.dll %publish:OutputPath%" ]
  }
}

This will locate packages folder (maybe different for your setup) and copy it to the output folder for the publish command.

Running Scripts Pre and Post Publish in ASP.NET Core RC2

This week I ran into an issue when deploying a Service Fabric service where a library file was not being copied to the output directory. Since I am using ASP.NET Core for my API layer in the Service Fabric project, I had to go dig around to figure out how to get the file to copy to the deployment folder during the publishing of the ASP.NET Core application.

note that this solution with project.json may change with as ASP.NET Core moves back to .csproj file

What I learned is that in ASP.NET Core RC 2 you can add scripts to the prepublish and postpublish events by adding a scripts section to the project.json file. In my case I needed to copy a file to the deployment folder after the rest of the project as built.

{
  "buildOptions": {
       // ...
    }
  },

  //...

  "scripts": {
    "prepublish": ["<command1>, <command2>"],
    "postpublish": [ "xcopy <pathtofile> %publish:OutputPath%" ]
  }
}

Note that you can reference variables like %publish:OutputPath%. You can also supply multiple commands by separating them with a comma. As noted above this currently works in ASP.NET Core RC2 but might change when as we transition back to the .csproj file.

Integrating ASP.NET Core with Service Fabric using ICommunicationListener

At the time of writing there is no official template for integrating ASP.NET Core (RC2) with Service Fabric in a Stateless Service so I though I would dive in and see if I could get it to work by looking at the ASP.NET 4.6 Web API Template that is currently available through Visual Studio. There will be a ASP.NET Core template available eventually but I thought this would be a useful exercise to learn more about how Service Fabric integrates with frameworks like ASP.NET.

You can find the full implementation of the solution I came up with on GitHub. There were also a couple examples that I used for reference. The first was a really basic template on GitHub which I used as my starting point to creating an ASP.NET Core Communication Listener. The other was the more advance solution that shows not only how to integrate but also build an API Gateway after the Microservices Gateway pattern.

ICommunicationListener

Lets take a look at the Service Fabric’s ICommunicationListener interface which provides a few basic benefits.

First, it allows for service communication in an agnostic manner. This means you can communicate with HTTP, UDP, or another other custom protocol you might need for your application by implementing this interface. You can even communication with more than one protocol for one service.

Another benefit it offers is allowing for your service to be moved without affecting any clients that are working with it. Any given service can move to another server because of machine failure, upgrade, resource balancing, etc., causing a change in the IP address of the actual service. By implementing this interface you are saved from having to manage any of those situations, instead Service Fabric manages it for you.

The ICommunicationListener interface accomplishes this by registering your service with the Service Fabric Naming Service which will then keep track of the endpoint locations where the services are located. This means a client can ask the Naming Service for a service by name and will be given the correct address without the need to know which machine it is actually running on (think along the same lines as DNS).

It achieves this through a simple interface ICommunicationListener which has three methods:

  • Abort - exit immediately, cancelling current requests
  • CloseAsync - stop taking any new requests, close current requests gracefully and then exit
  • OpenAsync - Open listener to be able to accept and send messages

As you can see it is a fairly simple interface but is a power concept because of the ability to allow for any type of communication and even multiple protocols per service.

Building an ASP.NET Core Communication Listener

The first method we will implement is the OpenAsync Method. In the case of the ASP.NET Core Communication Listener, this method will be responsible for starting the web service and binding it to the correct URL. But first we need to gather some information about where the service is running from Service Fabric.

Gathering Service Fabric Information

Since our service could be running on any server inside our cluster we need to get some of this information from Service Fabric runtime. We use the FabricRuntime class to get the CodePackageActivationContext and NodeContext which contains information like the current service protocol, current IPAddress, and port. We can get this information and format it appropriately by doing the following:

var endpoint = FabricRuntime.GetActivationContext().GetEndpoint(endpointName);

string serverUrl = $"{endpoint.Protocol}://{FabricRuntime.GetNodeContext().IPAddressOrFQDN}:{endpoint.Port}";

The endpointName variable is being passed in from the initial creation of the service in the program.cs file. It is any arbitrary name you decide to give the service. Take a look at how this all come together in the full solution on the GitHub repository.

Starting ASP.NET

At it’s heart ASP.NET Core is actually a command line console application. To start an ASP.NET application we use the WebHostBuilder class. You can find an implementation of this in the ASP.NET Core RC2 template that ships with Visual Studio. We are going to use slightly different setup than that template; The main differences are that we don’t need to use IIS Integration and we need to specify the serverUrl that we just generated with the Service Fabric runtime information:

var host = new WebHostBuilder()
                .UseKestrel()
                .UseContentRoot(Directory.GetCurrentDirectory())
                .UseStartup<Startup>()
                .UseUrls(serverUrl)
                .Build();

host.Run();

Implementing Open

Now that we know have the current URL of the service and know how to start the ASP.NET server, we can finish our implementation of the OpenAsync method.

This is just bringing together the previous two pieces and returning a server Url as a string. The return value of the OpenAsync method will be the address that is registered with the Service Fabric Naming Service allowing for the service to move around in the case of machine failure, upgrades, etc.

Here is what the whole OpenAsync Method looks like:

 public Task<string> OpenAsync(CancellationToken cancellationToken)
{
    var endpoint = FabricRuntime.GetActivationContext().GetEndpoint(endpointName);
    string serverUrl = $"{endpoint.Protocol}://{FabricRuntime.GetNodeContext().IPAddressOrFQDN}:{endpoint.Port}";


    webHost = new WebHostBuilder
                    .UseKestrel()
                    .UseContentRoot(Directory.GetCurrentDirectory())
                    .UseStartup<Startup>()
                    .UseUrls(serverUrl)
                    .Build();

    webHost.Start();

    return Task.FromResult(serverUrl);
}

Implementing Abort and Close

We still need to implement two more methods on the ICommunicationListener before we are finished: Abort and CloseAsync. These are fairly simple implementations and just require us to dispose of the WebHost object. You could get fancier and make sure all requests are handled but for right now we will just shut down the web service as that is what is done in the ASP.NET Web API template currently.

public void Abort()
{
    if (webHost != null)
    {
        webHost.Dispose();
    }

}

public Task CloseAsync(CancellationToken cancellationToken)
{
    if (webHost != null)
    {
        webHost.Dispose();
    }

    return Task.FromResult(true);
}

Register the Asp.Net Core Communication Listener with Service Fabric

We have created the Asp.Net Core Communication Listener but still need to register it with the StatelessService that will be using ASP.NET. There is a method on the StatelessSerivice Class that you can overload to return make the connection.

This is the integration point between Service Fabric and Asp.Net. In the case of Stateless service this returns the an array of ServiceInstanaceListners.

In the StatelessService class, override the CreateServiceInstanceListeners:

internal sealed class WebHostingService : StatelessService
{
    private readonly string _endpointName;

    public WebHostingService(StatelessServiceContext serviceContext, string endpointName)
        : base(serviceContext)
    {
        _endpointName = endpointName;
    }

    protected override IEnumerable<ServiceInstanceListener> CreateServiceInstanceListeners()
    {
        return new[] { new ServiceInstanceListener(serviceContext => new AspnetCoreCommunicationListener(_endpointName)) };
    }
}

Next steps

This is a simple implementation of an Asp.net Core Communication Listener for Service Fabric. If you would like to see the full working sample, check out this GitHub repository. I have implemented everything we talked about but also started to add in the ability to unit test the AspNetCoreCommunicationListener.

Eventually there will be a template that Visual Studio will ship with that will provide a default implementation. The defualt will be a likely good choice for getting started but this exercise of working through how to implement a ICommunicationListner is a good introduction to the ICommunicationListener interface and helps us better understand another aspect of the Service Fabric platform.