Migrating an ASP.NET Core RC1 Microservice to RC2

In a recent blog post, I talked about how to deploy an ASP.NET Core RC1 service to the cloud. With yesterday’s release of ASP.NET Core RC2, I had to make a number of minor changes to my code in order to get it working both locally and in the cloud.

The biggest change between RC1 and RC2 is an architectural change. In RC1, the thing responsible for prepping the application was inside the dnx tool, and it was tightly coupled to the notion of building web applications. In Rc2, we’re actually returning to a more explicit model with a Program class and a Main(), where we write our own code to construct the WebHostBuilder instead of it being done implicitly on our behalf.

First, there are changes to the structure of the project.json file. Rather than go through them all, I’m just going to point you to the modified project.json for the Zombies service. The easiest thing to do is to take a project.json file created by new RC2 tooling and use that as a template to adapt your existing file.

The next thing I did was add a Program class. You’ll notice that I use the AddStartup() method to invoke all of the old startup code I had from RC1:

using System;
using System.Collections.Generic;
using System.IO;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.Configuration;

namespace SampleMicroservice
{
  public class Program
  {
    public static void Main(string[] args)
    {
      var config = new ConfigurationBuilder()
        .AddCommandLine(args)
        .Build();

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

      host.Run();
    }
  }
}

The next change is that I had to use the AddCommandLine() method. Without this, our application isn’t going to respond to or care about the –server.urls parameter that is going to get passed to it by the buildpack when we push to Cloud Foundry.

I had to make a few tiny little changes to the Startup class, but it remains essentially unchanged:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace SampleMicroservice
{
    public class Startup
    {
        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: true, reloadOnChange: false)
                .AddJsonFile("ZombieConfig.json", optional: true, reloadOnChange: false)
                .AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public IConfigurationRoot Configuration { get; set; }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();
            services.AddOptions();
            services.Configure<ZombieOptions>(Configuration);

            services.AddScoped<IZombieRepository, ZombieRepository>();
            services.AddSingleton<IGlobalCounter, GlobalCounter>();
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();
            app.UseMvc();
        }
    }
}

The Configure<ZombieOptions>() method is supported by the same extension method as in RC1, except this method is in a new package, so we had to add a dependency on Microsoft.Extensions.Options.ConfigurationExtensions to our project.json.

With all this in place, we can simply run dotnet restore then dotnet build and finally cf push and that’s that… our app is now running on RC2 in Cloud Foundry.

All of the code for the RC2 version of this app can be found in my github repository.