asp.net core监控—引入Prometheus（三）

　　上一篇博文中说到Prometheus有四种指标类型：Counter（计数器）、Gauge（仪表盘）、Histogram（直方图）、Summary（摘要），并且我们做了一个Counter的Demo，接下来看看Gauge。

2、Gauge：仪表盘，有增有减

　　这个指标非常像汽车的车速表，指针是在一定范围内有增有减的。下面我们接着上一篇博文的Sample来说，现在需要实时监控处在下“单完成”，“支付完成”，“发货完成”的单据数据，和各三种状态的占比；我们知道一个订单在一个时刻只能是一种状态，我们可以在下单时增加计数order的指标，但当订单从order转到pay状态后，pay指标会增加，同时order指标会减少，这个场景就会用上了Gauge了。

　　有了这个思路，我们可以上手代码了，BusinessController的代码不变（因为我们实现了业务逻辑代码和监控数据指标采集分离），这里我们需要在MetricsHub.cs中添加Gauge类型的指标收集集合：

 public class MetricsHub
    {
        private static Dictionary<string, Counter> _counterDictionary = new Dictionary<string, Counter>();
        private static Dictionary<string, Dictionary<string, Gauge>> _gaugeDictionary = new Dictionary<string, Dictionary<string, Gauge>>();
        public Counter GetCounter(string key)
        {
            if (_counterDictionary.ContainsKey(key))
            {
                return _counterDictionary[key];
            }
            else
            {
                return null;
            }
        }
        public Dictionary<string, Gauge> GetGauge(string key)
        {
            if (_gaugeDictionary.ContainsKey(key))
            {
                return _gaugeDictionary[key];
            }
            else
            {
                return null;
            }
        }
        public void AddCounter(string key, Counter counter)
        {
            _counterDictionary.Add(key, counter);
        }
        public void AddGauge(string key, Dictionary<string, Gauge> gauges)
        {
            _gaugeDictionary.Add(key, gauges);
        }
    }

　　因为在上面分析中，我们一个动作，比如pay时，会触发两个指标的改变，order指标减少，pay指标增加，所以Gauge是一个Dictionary<string, Dictionary<string, Gauge>>类型，内部的字典存放减少和增加的Gauge的监控指标对象。

　　接下来就要在BusinessMetricsMiddleware的中间件中添加处理Gauge指标增加减少的代码了：

using Microsoft.AspNetCore.Http;
using PrometheusSample.Models;
using System.IO;
using System.Threading.Tasks;

namespace PrometheusSample.Middlewares
{
    /// <summary>
    /// 请求记录中间件
    /// </summary>
    public class BusinessMetricsMiddleware
    {

        private readonly RequestDelegate _next;
        public BusinessMetricsMiddleware(RequestDelegate next)
        {
            _next = next;
        }
        public async Task InvokeAsync(HttpContext context, MetricsHub metricsHub)
        {
            var originalBody = context.Response.Body;
            try
            {
                using (var memStream = new MemoryStream())
                {
                    //从管理返回的Response中取出返回数据，根据返回值进行监控指标计数
                    context.Response.Body = memStream;
                    await _next(context);
                    memStream.Position = 0;
                    string responseBody = new StreamReader(memStream).ReadToEnd();
                    memStream.Position = 0;
                    await memStream.CopyToAsync(originalBody);
                    if (metricsHub.GetCounter(context.Request.Path) != null || metricsHub.GetGauge(context.Request.Path) != null)
                    {
                        //这里约定所有action返回值是一个APIResult类型
                        var result = System.Text.Json.JsonSerializer.Deserialize<APIResult>(responseBody, new System.Text.Json.JsonSerializerOptions { PropertyNameCaseInsensitive = true });
                        if (result != null && result.Result)
                        {
                            //获取到Counter
                            var counter = metricsHub.GetCounter(context.Request.Path);
                            if (counter != null)
                            {
                                //计数
                                counter.Inc();
                            }

                            var gauges = metricsHub.GetGauge(context.Request.Path);
                            if (gauges != null)
                            {
                                //存在增加指标+就Inc
                                if (gauges.ContainsKey("+"))
                                {
                                    gauges["+"].Inc();
                                } 
                                //存在减少指标-就Dec
                                if (gauges.ContainsKey("-"))
                                {
                                    gauges["-"].Dec();
                                }
                            }
                        }
                    }
                }
            }
            finally
            {
                context.Response.Body = originalBody;
            }

        }
    }
}

　　再就是在Starsup中配置对应url的Gauge参数了：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.OpenApi.Models;
using Prometheus;
using PrometheusSample.Middlewares;
using PrometheusSample.Services;
using System.Collections.Generic;
namespace PrometheusSample
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }
        public IConfiguration Configuration { get; }
        public void ConfigureServices(IServiceCollection services)
        {
            MetricsHandle(services);
            services.AddScoped<IOrderService, OrderService>();
            services.AddControllers();
            services.AddSwaggerGen(c =>
            {
                c.SwaggerDoc("v1", new OpenApiInfo { Title = "PrometheusSample", Version = "v1" });
            });
        }
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseSwagger();
                app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "PrometheusSample v1"));
            }
            app.UseRouting();
            //http请求的中间件
            app.UseHttpMetrics();
            app.UseAuthorization();
            //自定义业务跟踪
            app.UseBusinessMetrics();
            app.UseEndpoints(endpoints =>
            {
                //映射监控地址为  /metrics
                endpoints.MapMetrics();
                endpoints.MapControllers();
            });
        }
        /// <summary>
        /// 处理监控事项
        /// </summary>
        /// <param name="services"></param>
        void MetricsHandle(IServiceCollection services)
        {
            var metricsHub = new MetricsHub();
            //counter
            metricsHub.AddCounter("/register", Metrics.CreateCounter("business_register_user", "注册用户数。"));
            metricsHub.AddCounter("/order", Metrics.CreateCounter("business_order_total", "下单总数。"));
            metricsHub.AddCounter("/pay", Metrics.CreateCounter("business_pay_total", "支付总数。"));
            metricsHub.AddCounter("/ship", Metrics.CreateCounter("business_ship_total", "发货总数。"));

            //gauge
            var orderGauge = Metrics.CreateGauge("business_order_count", "当前下单数量。");
            var payGauge = Metrics.CreateGauge("business_pay_count", "当前支付数量。");
            var shipGauge = Metrics.CreateGauge("business_ship_count", "当前发货数据。");
            metricsHub.AddGauge("/order", new Dictionary<string, Gauge> {
                { "+", orderGauge}
            });
            metricsHub.AddGauge("/pay", new Dictionary<string, Gauge> {
                {"-",orderGauge},
                {"+",payGauge}
            });
            metricsHub.AddGauge("/ship", new Dictionary<string, Gauge> {
                {"+",shipGauge},
                {"-",payGauge}
            });
            services.AddSingleton(metricsHub);
        }
    }
}