一.实现前的准备

• 以下是实现简单负载均衡的思路，图中的服务器均为虚拟机
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• 三台Linux服务器，一台用作Nginx负载均衡（192.168.254.139），另外两台用作Asp.Net Core应用程序承载的服务器（192.168.254.140，192.168.254.141）
• 一台用作于Client的Windows服务器。
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二.环境搭建

1.Asp.Net Core程序

 就是一个新建的空web应用程序，然后修改了下Startup的中间件，分别部署到2台Ubuntu上。

    public class Startup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application,visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app,IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.Run(async (context) =>
            {
                //await context.Response.WriteAsync("this is first web application");
                await context.Response.WriteAsync("this is second web application");
            });
        }
    }

2.配置Nginx服务器

• 安装Nginx
  • 在Ubuntu终端使用 sudo apt-get install Nginx 命令安装Nginx。
  • 然后通过 sudo service Nginx start 命令启动服务
  • 确认浏览器显示Nginx默认登录页。可在http://192.168.254.139/index.Nginx-debian.html 访问登录页面。
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  • 配置Nginx
    • 若要将 Nginx 配置为反向代理以将请求转接到 ASP.NET Core 应用，请修改 /etc/Nginx/sites-available/default。 sudo vi /etc/Nginx/sites-available/default 
    • 设置proxy_pass后面的参数
    • 新增upstream，表示要转接的服务器集合，upstream后面的名字要与proxy_pass后面的参数相对应
    • 修改完之后:wq保存，然后 sudo Nginx -t 来验证配置文件的语法有没有错误，如果配置文件测试成功，可以通过运行  sudo Nginx -s reload  强制 Nginx 选取更改
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    upstream cluster.com{ server 192.168.254.140 weight=1; server 192.168.254.141 weight=1; }       
    
    server {
            listen 80 default_server;
            # listen [::]:80 default_server deferred;
            # SSL configuration
            #
            # listen 443 ssl default_server;
            # listen [::]:443 ssl default_server;
            #
            # Note: You should disable gzip for SSL traffic.
            # See: https://bugs.debian.org/773332
            #
            # Read up on ssl_ciphers to ensure a secure configuration.
            # See: https://bugs.debian.org/765782
            #
            # Self signed certs generated by the ssl-cert package
            # Don‘t use them in a production server!
            #
            # include snippets/snakeoil.conf;
    
            root /var/www/html;
    
            # Add index.PHP to the list if you are using PHP
            index index.html index.htm index.Nginx-debian.html;
    
            server_name _example.com *.example.com;
    
            location / {
                    proxy_pass http://cluster.com;
                    proxy_http_version 1.1;
                    proxy_set_header   Upgrade $http_upgrade;
                    proxy_set_header   Connection keep-alive;
                    proxy_set_header   Host $host;
                    proxy_cache_bypass $http_upgrade;
                    proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
                    proxy_set_header   X-Forwarded-Proto $scheme;
                    # First attempt to serve request as file,then
                    # as directory,then fall back to displaying a 404.
                    try_files $uri $uri/ =404;
            }
    
            # pass PHP scripts to FastCGI server
            #
            #location ~ \.PHP$ {
            #       include snippets/fastcgi-PHP.conf;
            #
            #       # With PHP-fpm (or other unix sockets):
            #       fastcgi_pass unix:/var/run/PHP/PHP7.0-fpm.sock;
            #       # With PHP-cgi (or other tcp sockets):
            #       fastcgi_pass 127.0.0.1:9000;
            #}
    
            # deny access to .htaccess files,if Apache‘s document root
            # concurs with Nginx‘s one
            #
            #location ~ /\.ht {
            #       deny all;
            #}
    }

    2.Client控制台应用程序

        class Program
        {
            static void Main(string[] args)
            {
                HttpClient httpClient = new HttpClient();
                for (int i = 0; i < 1000; i++)
                {
                    string result = httpClient.GetStringAsync("http://192.168.254.139").Result;
                    Console.WriteLine(result);
                }
                Console.ReadKey();
            }
        }

    结果如下：

    

    由结果可知，Nginx服务器会根据我们配置Nginx时的权重进行转向，到现在，一个简单的集群已经搭建。