package nameresolution

type Resolver interface {
    Init(metadata Metadata) error
    ResolveID(req ResolveRequest) (string, error)
}

type Metadata struct {
    Properties    map[string]string `json:"properties"`
    Configuration interface{}
}

type ResolveRequest struct {
    ID        string
    Namespace string
    Port      int
    Data     map[string]string
}

三、模拟服务注册与负载均衡

public class HomeController: Controller
{
    private static readonly ConcurrentDictionary<string, EndpointCollection> _applications = new();

    [HttpPost("/register")]
    public IActionResult Register([FromBody] RegisterRequest request)
    {
        var appId = request.Id;
        var endpoints = _applications.TryGetValue(appId, out var value) ? value : _applications[appId] = new();
        endpoints.TryAdd(request.HostAddress, request.Port);
        Console.WriteLine($"Register {request.Id} =>{request.HostAddress}:{request.Port}");
        return Ok();
    }

    [HttpPost("/resolve")]
    public IActionResult Resolve([FromBody] ResolveRequest request)
    {
        if (_applications.TryGetValue(request.ID, out var endpoints) && endpoints.TryGet(out var endpoint))
        {
            Console.WriteLine($"Resolve app {request.ID} =>{endpoint}");
            return Content(endpoint!);
        }
        return NotFound();
    }
}

public class EndpointCollection
{
    private readonly List<string> _endpoints = new();
    private int _index = 0;
    private readonly object _lock = new();

    public bool TryAdd(string ipAddress, int port)
    {
        lock (_lock)
        {
            var endpoint = $"{ipAddress}:{port}";
            if (_endpoints.Contains(endpoint))
            {
                return false;
            }
            _endpoints.Add(endpoint);
            return true;
        }
    }

    public bool TryGet(out string? endpoint)
    {
        lock (_lock)
        {
            if (_endpoints.Count == 0)
            {
                endpoint = null;
                return false;
            }
            _index++;
            if (_index >= _endpoints.Count)
            {
                _index = 0;
            }
            endpoint = _endpoints[_index];
            return true;
        }
    }
}

HomeController提供了两个Action方法，Register方法用来注册应用，自定义Resolver的Init方法会调用它。另一个方法Resolve则用来完成根据请求的应用表示得到一个具体的终结点，自定义Resolver的ResolveID方法会调用它。这两个方法的参数类型RegisterRequest和ResolveRequest定义如下，后者和前面给出的同名接口具有一致的定义。两个Action都会在控制台输出相应的文字显示注册的应用信息和解析出来的终结点。

public class RegisterRequest
{
    public string Id { get; set; } = default!;
    public string HostAddress { get; set; } = default!;
    public int Port { get; set; }
}

public class ResolveRequest
{
    public string ID { get; set; } = default!;
    public string? Namespace { get; set; }
    public int Port { get; }
    public Dictionary<string, string> Data { get; } = new();
}

四、自定义NameResolution组件

// Name resolutions.
nr "github.com/dapr/components-contrib/nameresolution"
nr_consul "github.com/dapr/components-contrib/nameresolution/consul"
nr_kubernetes "github.com/dapr/components-contrib/nameresolution/kubernetes"
nr_mdns "github.com/dapr/components-contrib/nameresolution/mdns"
nr_svcreg "github.com/dapr/components-contrib/nameresolution/svcreg"

runtime.WithNameResolutions(
	nr_loader.New("svcreg", func() nr.Resolver {
		return nr_svcreg.NewResolver(logContrib)
	}),
	nr_loader.New("mdns", func() nr.Resolver {
		return nr_mdns.NewResolver(logContrib)
	}),
	nr_loader.New("kubernetes", func() nr.Resolver {
		return nr_kubernetes.NewResolver(logContrib)
	}),
	nr_loader.New("consul", func() nr.Resolver {
		return nr_consul.NewResolver(logContrib)
	}),
),

六、编译部署daprd.exe

replace (
	go.opentelemetry.io/otel => go.opentelemetry.io/otel v0.20.0
	gopkg.in/couchbaselabs/gocbconnstr.v1 => github.com/couchbaselabs/gocbconnstr v1.0.5
	k8s.io/client => github.com/kubernetes-client/go v0.0.0-20190928040339-c757968c4c36
	github.com/dapr/components-contrib => ../components-contrib
)

在将当前目录切换到“dapr/cmd/daprd/”后，以命令行的方式执行“go build”后会在当前目录下生成一个daprd.exe可执行文件。现在我们需要使用这个新的daprd.exe将当前使用使用的替换掉，该文件所在的目录在“%userprofile%.dapr\bin”。

七、配置svcreg

apiVersion: dapr.io/v1alpha1
kind: Configuration
metadata:
  name: daprConfig
spec:
  nameResolution:
    component: "svcreg"
    configuration:
      endpointAddress: http://127.0.0.1:3721
  tracing:
    samplingRate: "1"
    zipkin:
      endpointAddress: http://localhost:9411/api/v2/spans

八、测试效果

 using Microsoft.AspNetCore.Mvc;
 using Shared;

 var app = WebApplication.Create(args);
 app.MapPost("{method}", Calculate);
 app.Run("http://localhost:9999");

 static IResult Calculate(string method, [FromBody] Input input)
 {
     var result = method.ToLower() switch
     {
         "add" => input.X + input.Y,
         "sub" => input.X - input.Y,
         "mul" => input.X * input.Y,
         "div" => input.X / input.Y,
         _ => throw new InvalidOperationException($"Invalid method {method}")
     };
     return Results.Json(new Output { Result = result });
 }
public class Input
{
    public int X { get; set; }
    public int Y { get; set; }
}

public class Output
{
    public int 		Result { get; set; }
    public DateTimeOffset 	Timestamp { get; set; } = DateTimeOffset.Now;
}

具有如下定义的App1是一个控制台程序，它利用Dapr客户端SDK调用了上诉四个API。

 using Dapr.Client;
 using Shared;

 HttpClient client = DaprClient.CreateInvokeHttpClient(appId: "app2");
 var input = new Input(2, 1);

 await InvokeAsync("add", "+");
 await InvokeAsync("sub", "-");
 await InvokeAsync("mul", "*");
 await InvokeAsync("div", "/");

 async Task InvokeAsync(string method, string @operator)
 {
     var response = await client.PostAsync(method, JsonContent.Create(input));
     var output = await response.Content.ReadFromJsonAsync<Output>();
     Console.WriteLine( $"{input.X} {@operator} {input.Y} = {output.Result} ({output.Timestamp})");
 }

在启动ServiceRegistry之后，我们启动App2，控制台上会阐述如下的输出。从输出的NameResolution组件名称可以看出，我们自定义的svcreg正在被使用。

由于应用启动的时候会调用Resolver的Init方法进行注册，这一点也反映在ServiceRegistry如下所示的输出上。可以看出注册实例的AppID为”app2”，对应的终结点为“10.181.22.4:60840”。

然后我们再启动App1，如下所示的输出表明四次服务调用均成功完成。

启动的App1的应用实例同样会在ServiceRegistry中注册。而四次服务调用会导致四次针对Resolver的ResolveID方法的调用，这也体现在ServiceRegistry的输出上。