RabbitMQ是以Erlang所編寫的Message broker， 支援的語言相當的廣泛。Spring boot/cloud跟Steeltoe的Message broker也是使用Rabbit MQ，來寫個小小的練習體驗一下非同步通訊跟技術異質性，使用Web API來call另一個Console專案的服務

依據RabbitMQ官網的指示在windows跟專案安裝完RabbitMQ跟相關的nuget套件後，
首先加入一個web api controller名為SayHelloController
然後在RabbitMQ的部分，先建立起connection --> 建立channel-->設定Queue的名字-->publish message

using System.Text;
using Microsoft.AspNetCore.Mvc;
using RabbitMQ.Client;

namespace APIGateway.Controllers
{
    [Produces("application/json")]
    [Route("api/SayHello")]
    public class SayHelloController : Controller
    {        
        // POST: api/SayHello
        [HttpPost]
        public string Post([FromQuery]string name)
        {
            var factory = new ConnectionFactory() { HostName = "localhost" };

            using (var connection = factory.CreateConnection()) {
                using (var channel = connection.CreateModel()) {
                    channel.QueueDeclare(
                        queue: "hello",
                        exclusive: false,
                        autoDelete: false,
                        arguments: null
                        );

                    string message = name;
                    var body = Encoding.UTF8.GetBytes(message);

                    channel.BasicPublish(
                        exchange: "",
                        routingKey: "hello", basicProperties: null,
                        body: body);
                }
            }
            return $"Hello,{name}";
        }
    }
}

加入一個新的Console專案，名為SayHelloService
在Program.cs裡面 編寫consumer相關的代碼

using RabbitMQ.Client;
using RabbitMQ.Client.Events;
using System;
using System.Text;

namespace SayHelloService
{
    class Program
    {
        static void Main(string[] args) {
            SubscribeToAPIGateway();
        }

        private static void SubscribeToAPIGateway() {
            var factory = new ConnectionFactory() { HostName = "localhost" };
            using (var connection = factory.CreateConnection())
            using (var channel = connection.CreateModel()) {
                channel.QueueDeclare(
                    queue: "hello",
                    durable: false,
                    exclusive: false,
                    autoDelete: false,
                    arguments: null);

                var consumer = new EventingBasicConsumer(channel);
                consumer.Received += (model, ea) =>
                {
                    var body = ea.Body;
                    var message = Encoding.UTF8.GetString(body);
                    Console.WriteLine($"Received: {message}");
                    Console.WriteLine($"Hello, {message}");
                };

                channel.BasicConsume(
                    queue: "hello",
                    autoAck: true,
                    consumer: consumer);

                Console.WriteLine("Pess any key to exit");
                Console.ReadLine();
            }
        }
    }
}

補充一點是channel.BasicConsume中的參數將autoAck設為true，RabbitMQ才會將consumer接到的該消息從queue移除。

啟用API gateway的服務後，啟用SayHelloService服務
在browser的網址輸入 http://localhost:{API_Gateway_port}/api/SayHello?name=John
會看到SayHelloService的console印出 Hello, John

ps:看RabbitMQ的文件花掉好多時間，光是RabbitMQ就好多東西了，本來還想試著用RabbitMQ取代之前用的restful wpi來做service registry。