HystrixCommand看名字就知道是Command pattern

原本UI會直接call後端的service，現在插入一個command將UI跟service解耦，同時在command中判斷service是否異常決定是否要執行callbackㄝ, 以及丟出監測的資料

把練習的APIGateway專案加入Hystrix

首先加入nuget package

• Steeltoe.CircuitBreaker.Hystrix;
• Steeltoe.CircuitBreaker.Hystrix;

在appsettings.json加入設定

  "hystrix": {
    "stream": {
      "validate_certificates": false
    },
    "command": {
      "FortuneService": {
        "threadPoolKeyOverride": "FortuneServiceTPool"
      }
    }

在Startup.cs加入HystrixCommand跟Dashboard用的設定

        public void ConfigureServices(IServiceCollection services) {
           .........................................
           .........................................
            // Add services for Hystrix
            services.AddHystrixCommand<GetProductCommand>("ProductService", Configuration);
            services.AddHystrixCommand<GetProductsCommand>("ProductService", Configuration);
            services.AddHystrixMetricsStream(Configuration);
        }
        
       public void Configure(IApplicationBuilder app, IHostingEnvironment env,
            IApplicationLifetime appLifetime) {
            ........................................
            ........................................
            app.UseHystrixRequestContext(); 
            app.UseHystrixMetricsStream();
        }         

Sample code是用非同步寫的，這邊改用同步來寫。

在資料夾Services底下新增一個GetProductCommand.cs來處理依據ID取值的request

    public class GetProductCommand : HystrixCommand<string>
    {
        private readonly IHystrixCommandOptions options;
        private readonly IProductService productService;
        private int id;
        public GetProductCommand(IHystrixCommandOptions options, IProductService productService) : base(options) {
            this.options = options;
            this.productService = productService;
            IsFallbackUserDefined = true;
        }

        public string GetProduct(int id) {
            this.id = id;
            return Execute();
        }

        protected override string Run() {

            return productService.GetValue(this.id);
        }

        protected override string RunFallback() {
            return "Error";
        }
    }

在資料夾Services底下另新增一個GetProductsCommand.cs來處理取回全部Product的request

    public class GetProductsCommand:HystrixCommand<string[]>
    {
        private readonly HystrixCommandOptions options;
        private readonly IProductService productService;

        public GetProductsCommand(HystrixCommandOptions options, IProductService productService) : base(options) {
            this.options = options;
            this.productService = productService;
            IsFallbackUserDefined = true;
        }

        public string[] GetProducts() {
            return Execute();
        }

        protected override string[] Run() {

            return productService.GetValues();
        }

        protected override string[] RunFallback() {
            return new string[] { "Error", "Error" };
        }
    }

將ValuesController更名為ProductsController然後注入command使用

    [Route("api/[controller]")]
    public class ProductsController : Controller
    {
    private readonly GetProductCommand getProductCommand;
    private readonly GetProductsCommand getProductsCommand;

    // GET: api/products
    public ProductsController(GetProductCommand getProductCommand, GetProductsCommand getProductsCommand) {
      this.getProductCommand = getProductCommand;
      this.getProductsCommand = getProductsCommand;
    }

    [HttpGet]
    public IEnumerable<string> Get()
    {
      return getProductsCommand.GetProducts();
    }

    // GET api/products/5
    [HttpGet("{id}")]
        public string Get(int id) {
            Console.WriteLine("Execute Get Product");
            return getProductCommand.GetProduct(id);
        }
    }

啟動APIGateway,不啟動ProdutsService這時候開browser會看到下面

證明fallback有作用

ps: 跟Dashboard的通訊又有問題了...抓到了在回頭修改文章....