Configuring Port as part of Service Registration

[dealproc]

I need to configure a dynamic port as part of my service registration during a generic host startup sequence. According to the dotnet docs, if you say your binding port is "0", then it'll allocate a dynamic port for you. My problem is how do I do this within the registration apis?

[marcin-krystianc]

Hi, as far as I understand your use case you should:

• Bind the service to port "0"
• Start the service
• Read which actual port it was assigned to
• Provide an actual port to the registration API

Is it what you were after?

[bidianqing]

I have the same problem. How to get dynamic port in Startup.ConfigureServices method?

[dealproc]

Yeah, I had to do exactly what you mention @marcin-krystianc. In order to achieve it, I had to build an alternative method to AgentServiceRegistration that looks like this:

namespace Consul.AspNetCore {
    using System.Threading;
    using System.Threading.Tasks;

    using Microsoft.AspNetCore.Hosting.Server;
    using Microsoft.AspNetCore.Hosting.Server.Features;
    using Microsoft.Extensions.DependencyInjection;
    using Microsoft.Extensions.Hosting;
    using Microsoft.Extensions.Logging;

    public class AgentServiceRegistrationWithDynamicPortHostedService : IHostedService {
        private readonly IServer _server;
        private readonly IConsulClient _consulClient;
        private readonly AgentServiceRegistration _serviceRegistration;
        private readonly ILogger _log;
        private readonly IHostApplicationLifetime _hostApplicationLifetime;

        public AgentServiceRegistrationWithDynamicPortHostedService(ILoggerFactory loggerFactory,
            IHostApplicationLifetime hostApplicationLifetime,
            IServer server,
            IConsulClient consulClient,
            AgentServiceRegistration serviceRegistration) {
            _log = loggerFactory.CreateLogger<AgentServiceRegistrationWithDynamicPortHostedService>();
            _hostApplicationLifetime = hostApplicationLifetime;
            _log.LogCritical("Logger instantiated.");
            _server = server;
            _consulClient = consulClient;
            _serviceRegistration = serviceRegistration;
        }

        public Task StartAsync(CancellationToken cancellationToken) {
            _hostApplicationLifetime.ApplicationStarted.Register(() => {
                _log.LogInformation("Registering with Consul.");
                var serverAddressesFeature = _server.Features.Get<IServerAddressesFeature>();
                _log.LogInformation("Number of Uris: {@NumberOfUris}", serverAddressesFeature.Addresses.Count);
                var possiblePorts = serverAddressesFeature.Addresses.Select(a => new Uri(a).Port).Distinct();
                _serviceRegistration.Port = possiblePorts.FirstOrDefault();
                _log.LogInformation("Reporting as bound to port: {@port}", _serviceRegistration.Port);

                _log.LogInformation("Updating endpoints, replacing {port} with actual port number.");
                if (_serviceRegistration.Check != null) {
                    _serviceRegistration.Check.HTTP = (_serviceRegistration.Check.HTTP ?? "").Replace("{port}", _serviceRegistration.Port.ToString());
                    _serviceRegistration.Check.TCP = (_serviceRegistration.Check.TCP ?? "").Replace("{port}", _serviceRegistration.Port.ToString());
                }
                foreach (var x in _serviceRegistration.Checks ?? new AgentServiceCheck[0]) {
                    x.HTTP = (x.HTTP ?? "").Replace("{port}", _serviceRegistration.Port.ToString());
                    x.TCP = (x.TCP ?? "").Replace("{port}", _serviceRegistration.Port.ToString());
                }

                _consulClient.Agent.ServiceRegister(_serviceRegistration, CancellationToken.None).GetAwaiter().GetResult();
            });

            return Task.CompletedTask;
        }

        public Task StopAsync(CancellationToken cancellationToken) {
            return _consulClient.Agent.ServiceDeregister(_serviceRegistration.ID, cancellationToken);
        }
    }

    public static class AdditionalServiceCollectionExtensions {
        public static IServiceCollection AddConsulServiceRegistrationWithDynamicPort(this IServiceCollection services, Action<AgentServiceRegistration> configure) {
            var registration = new AgentServiceRegistration();

            configure.Invoke(registration);

            return services
                .AddSingleton(registration)
                .AddHostedService<AgentServiceRegistrationWithDynamicPortHostedService>();
        }
    }
}

The key point with this... the app needs to be fully online before you can read the resolved IP Port and register. I didn't see an alternative way to gain the resolved IP. If someone has more information on how to better implement this, I'm game to listen and learn.