How to self register a service with Consul

Question

I'm trying to self register my ASP.NET Core application to Consul registry on startup and deregister it on shutdown.

From here I can gather that calling the http api [put /v1/agent/service/register] might be the way to go (or maybe not!).

From my app, I thought I'll target the Startup class, starting with adding the my .json file

public Startup(IHostingEnvironment env)
{
   var builder = new Configuration().AddJsonFile("consulconfig.json");
   Configuration = builder.Build();
}

But now, I'm stuck as ConfigureServices method tells me thats where I add services to the container, and Configure method is where I configure the Http request pipeline.

Anybody to point me in the right directions, online readings, examples, etc.

Answer 1

First of all I recommend to use Consul.NET to interact with Consul. Using it, a service registration may look like:

var registration = new AgentServiceRegistration
{
    Name = "foo",
    Port = 4242,
    Address = "http://bar"
};

using (var client = new ConsulClient())
{
    await client.Agent.ServiceRegister(registration);
}

Now let's integrate this code into ASP.NET Core startup process with help of DI and loose coupling. Read your json file into ConsulOptions instance (DTO without any logic):

public void ConfigureServices(IServiceCollection services)
{
    services.AddOptions();
    services.Configure<ConsulOptions>(Configuration);
}

Encapsulate all Consul-related logic in class ConsulService accepting ConsulOptions as a dependency:

public class ConsulService : IDisposable
{
    public ConsulService(IOptions<ConsulOptions> optAccessor) { }

    public void Register() 
    {
        //possible implementation of synchronous API
        client.Agent.ServiceRegister(registration).GetAwaiter().GetResult();
    }
}

Add the class itself to the DI container:

services.AddTransient<ConsulService>();

Then create an extention method of IApplicationBuilder and call it:

public void Configure(IApplicationBuilder app)
{
    app.ConsulRegister();
}

In ConsulRegister implementation we add our hooks on application start/stop:

public static class ApplicationBuilderExtensions
{
    public static ConsulService Service { get; set; }

    public static IApplicationBuilder ConsulRegister(this IApplicationBuilder app)
    {
        //design ConsulService class as long-lived or store ApplicationServices instead
        Service = app.ApplicationServices.GetService<ConsulService>();

        var life = app.ApplicationServices.GetService<IApplicationLifetime>();

        life.ApplicationStarted.Register(OnStarted);
        life.ApplicationStopping.Register(OnStopping);

        return app;
    }

    private static void OnStarted()
    {
        Service.Register(); //finally, register the API in Consul
    }
}

Locking absence and static fields are OK because the Startup class is executed exactly once on application start. Don't forget to de-register the API in OnStopping method!