一直以來都知道.netcore可以開始跨平台運作在linux上，因此運作在 docker的container中也是可行的

不過最近因為要研究apigateway，需要模擬infra的架構 ，因此需要在本機環境buildup起來多台主機的模式

沒想到入坑玩了一下，就發現，其實眉眉角角也不少，但來來回回操作後，其實是相對會愈來愈熟悉

首頁，我solution的構成包含了以下幾層 (apigateway還可做loadbalance，再加個nginx就可以, 不是這次的重點)

1.Redis(多台 instance作counter的cache)
2.WebApp(.net core)
3.ApiGateway(.net core + ocelot.net sdk)
4.Consul(service discovery service 作ha)

這次主要研究的機制為 3跟4之間的協作機制
基本上，有了3，預設走configuration就可以手動配置 ，但若要能做到動態ha的話，就必須加入service discovery的機制，剛好ocelot框架有支援 consul(還有其他套，但預設consul)

docker-compose

為了方便 重建，這次採用 docker-compose的yaml來維護(以下情境的container -name 都一般化了，只需要區分角色就好)

version: "3"

services:
  nginx:
    build: ./nginx
    container_name: core-app.local
    ports:
      - "80:80"
      - "443:443"
    depends_on:
      - core-app-gateway1
    # network_mode: "host"
    networks:
      - backend

  consul1:
    image: consul
    container_name: node1
    command: agent -server -bootstrap-expect=2 -node=node1 -bind=0.0.0.0 -client=0.0.0.0 -datacenter=dc1
    # network_mode: "host"
    networks:
      - backend

  consul2:
    image: consul
    container_name: node2
    command: agent -server -retry-join=node1 -node=node2 -bind=0.0.0.0 -client=0.0.0.0 -datacenter=dc1
    depends_on:
      - consul1
    # network_mode: "host"
    networks:
      - backend

  consul3:
    image: consul
    hostname: discover-center
    container_name: node3
    command: agent -retry-join=node1 -node=node3 -bind=0.0.0.0 -client=0.0.0.0 -datacenter=dc1 -ui
    ports:
      - 8500:8500
    depends_on:
      - consul1
      - consul2
    #network_mode: "host"
    networks:
      - backend

  redis:
    container_name: myredis
    image: redis:6.0.6
    restart: always
    ports:
      - 6379:6379
    privileged: true
    command: redis-server /etc/redis/redis.conf --appendonly yes
    volumes:
      - $PWD/data:/data
      - $PWD/conf/redis.conf:/etc/redis/redis.conf
    networks:
      - backend

  core-app-discover-a1:
    build: ./dotnetapp/dotnetapp-discover
    hostname: webapp1
    environment:
      - HOSTNAME=http://0.0.0.0:40001
      - SERVER_HOSTNAME=http://192.168.1.115
      - SERVER_PORT=8500
      - CLIENT_HOSTNAME=http://core-app-discover-a1
      - CLIENT_PORT=40001
      - SERVICE_NAME=core-app-discover-a
      - RedisConnection=redis:6379,password=12345678,allowAdmin=true
    depends_on:
      - redis
      - consul3
    ports:
      - "40001"
    networks:
      - backend

  core-app-discover-a2:
    build: ./dotnetapp/dotnetapp-discover
    hostname: webapp2
    environment:
      - HOSTNAME=http://0.0.0.0:40001
      - SERVER_HOSTNAME=http://192.168.1.115
      - SERVER_PORT=8500
      - CLIENT_HOSTNAME=http://core-app-discover-a2
      - CLIENT_PORT=40001
      - SERVICE_NAME=core-app-discover-a
      - RedisConnection=redis:6379,password=12345678,allowAdmin=true
    depends_on:
      - redis
      - consul3
    ports:
      - "40001"
    networks:
      - backend

  core-app-discover-a3:
    build: ./dotnetapp/dotnetapp-discover
    hostname: webapp3
    environment:
      - HOSTNAME=http://0.0.0.0:40001
      - SERVER_HOSTNAME=http://192.168.1.115
      - SERVER_PORT=8500
      - CLIENT_HOSTNAME=http://core-app-discover-a3
      - CLIENT_PORT=40001
      - SERVICE_NAME=core-app-discover-a
      - RedisConnection=redis:6379,password=12345678,allowAdmin=true
    depends_on:
      - redis
      - consul3
    ports:
      - "40001"
    networks:
      - backend

  core-app-discover-b:
    build: ./dotnetapp/dotnetapp-discover
    hostname: webapp-b
    environment:
      - HOSTNAME=http://0.0.0.0:50001
      - SERVER_HOSTNAME=http://192.168.1.115
      - SERVER_PORT=8500
      - CLIENT_HOSTNAME=http://core-app-discover-b
      - CLIENT_PORT=50001
      - SERVICE_NAME=core-app-discover-b
      - RedisConnection=192.168.1.115:6379,password=xxxxxxx
    depends_on:
      - redis
      - consul3
    ports:
      - "50001:50001"
    networks:
      - backend

  core-app-discover-c:
    build: ./dotnetapp/dotnetapp-discover
    hostname: webapp-c
    environment:
      - HOSTNAME=http://0.0.0.0:50002
      - SERVER_HOSTNAME=http://192.168.1.115
      - SERVER_PORT=8500
      - CLIENT_HOSTNAME=http://core-app-discover-c
      - CLIENT_PORT=50002
      - SERVICE_NAME=core-app-discover-c
      - RedisConnection=192.168.1.115:6379,password=xxxxxxx
    depends_on:
      - redis
      - consul3
    ports:
      - "50002:50002"
    networks:
      - backend

  core-app-gateway1:
    build: ./dotnetapp/dotnetapp-gateway
    hostname: gateway1
    environment:
      - HOSTNAME=http://0.0.0.0:20001
      - SERVER_HOSTNAME=http://192.168.1.115
      - SERVER_PORT=8500
      - CLIENT_HOSTNAME=http://192.168.1.115
      - CLIENT_PORT=20001
      - SERVICE_NAME=core-app-gateway1
    depends_on:
      - consul3
    ports:
      - 20001:20001
    networks:
      - backend

networks:
  backend:
    driver: bridge

以上yaml就會建立一個network讓 container之前可以用 hostname來通訊。

這次研究的過程，會發現一件事情就是若要綁service discovery，那麼每個末端的webapp都需要跟register center做註冊，並提供一個health接口。但是若要做到auto scale，那依賴docker-compose所做的scale就會綁定動態的host_name(有序號)，因此在此不建議 用scale直接長n台容器，而是先用多個端點來建置(如我的a1、a2、a3三台)
這樣就可以指定 hostname跟port給 webapp，而不會被scaling的機制而無法抓到動態的port跟名稱

.netcore application的Dockerfile

以下是webapp的dockerfile (gateway的打包方式差不多，就不貼了)

FROM mcr.microsoft.com/dotnet/sdk:6.0-alpine AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443

FROM mcr.microsoft.com/dotnet/sdk:6.0-alpine AS build
WORKDIR /src
COPY ["dotnetapp-discover.csproj", "dotnetapp-discover/"]
RUN dotnet restore "dotnetapp-discover/dotnetapp-discover.csproj"
COPY . ./dotnetapp-discover
WORKDIR "/src/dotnetapp-discover"
RUN dotnet build "dotnetapp-discover.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "dotnetapp-discover.csproj" -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "dotnetapp-discover.dll"]

為了計數器功能與多台sharing cache，因此這次 還 模擬了一下連redis
而redis的connection string 可以透過 environment variable 注入進來(docker-compose可以另外用.env的檔案來管理不同環境，有興趣可以看 官方文件)，而在.netcore的c#程式中，要抓到docker的參數的話可以使用GetEnvironmentVariable來取得設定值

    public static IServiceCollection AddCacheService(this IServiceCollection services)
    {
        var redisConnection = Environment.GetEnvironmentVariable("RedisConnection");
#if DEBUG
        redisConnection = "192.168.1.115:6379,password=xxxxxx,allowAdmin=true";
#endif
        
        services.AddSingleton<IConnectionMultiplexer>(
            ConnectionMultiplexer.Connect(redisConnection)
        );
        return services;
    }

註∶為了反覆測試，才加上allow admin，不然這個開關是很危險的，可以直接flush掉你的所有快取(清空)

Redis記錄的Log型態

註冊Service Discovery

ApiGateway跟WebApp我都有跟Consul註冊Service Discovery
因此這次主要的寫法也是follow consul client sdk的套件，Consul的註冊管理上，同一個Name的會被Grouping起來，ID要給不一樣的，若ServiceName都不一樣，就算是一樣的程式，還是會被視為不同節點，這樣會無法作HA的判斷

static void RegisterConsul(string serviceName, string serverHostName , string serverPort, string clientHostName , string clientPort, IHostApplicationLifetime appLifeTime)
{
    using var consulClient = new Consul.ConsulClient(p => 
        { p.Address = new Uri($"{serverHostName}:{serverPort}"); });
    var registration = new AgentServiceRegistration()
    {
        Check = new AgentServiceCheck()
        {
            Interval = TimeSpan.FromSeconds(10),
            HTTP = $"{clientHostName}{(clientPort == string.Empty ? "" : $":{clientPort}")}/health",
            Timeout = TimeSpan.FromSeconds(5),
            Method = "GET",
            Name = "check",
        },
        ID = Guid.NewGuid().ToString(),
        Name = serviceName,
        Address = Dns.GetHostName(),
        Port = int.Parse(clientPort),
        
    };

    try
    {
        consulClient.Agent.ServiceRegister(registration).Wait();
    }
    catch (Exception e)
    {
        Console.WriteLine(e);
    }

    //web服務停止時，向Consul解註冊
    consulClient.Agent.ServiceDeregister(registration.ID).Wait();
}

以上function可以在program.cs的startup時期先進行註冊，而這個function所有的參數一樣可以來自於 docker-compose
範例∶

自動生成HealthCheck端點

在webapp的startup可以使用以下語法就長出health接口

builder.Services.AddHealthChecks();

app.MapHealthChecks("/health",  new HealthCheckOptions()
{
    ResultStatusCodes =
    {
        [Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus.Healthy] = StatusCodes.Status200OK,
        [Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus.Degraded] = StatusCodes.Status200OK,
        [Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus.Unhealthy] = StatusCodes.Status503ServiceUnavailable
    }
});

但還是要視服務加上MapHealthChecks的ResultStatus的設定，以consul來說，就是回200就好了，若沒有加上這個設定，其實health的回應並不是200，所以會被視為失敗

正常情況打 health的接口

Ocelot的設定檔

最後就是ocelot的json設定，傳統的Ocelot自已就有Load-Balance機制，因此若有多台Downstream的服務，本來就可以用以下設定去管理服務

不過這樣做的缺點就是若隨時要增減 容器/主機時，都要再去重新配置設定檔。造成主機可能的reset與維運上的難度，因此透過Service Discovery的好處就浮上了臺面！以下的配置，只需要注意，不用定義DownStream的Host，只要給一個ServiceName，這個ServiceName要跟WebApp在Startup的時候註冊的一樣。並在最後GloablConfiguration有註冊Service DiscoveryProvider的設定，就可以打通ApiGateway跟Service Discovery之間的便利機制。

{
  "Routes": [
    {
      "DownstreamPathTemplate": "/test",
      "DownstreamScheme": "http",
      "UpstreamPathTemplate": "/newapi/get",
      "UpstreamHttpMethod": [
        "Get"
      ],
      "ServiceName": "core-app-discover-a",
      "LoadBalancerOptions": {
        "Type": "LeastConnection"
      }
    },
    {
      "DownstreamPathTemplate": "/test/list",
      "DownstreamScheme": "http",
      "UpstreamPathTemplate": "/newapi/list",
      "UpstreamHttpMethod": [
        "Get"
      ],
      "ServiceName": "core-app-discover-a",
      "LoadBalancerOptions": {
        "Type": "LeastConnection"
      }
    },
    {
      "DownstreamPathTemplate": "/test",
      "DownstreamScheme": "http",
      "DownstreamHttpMethod": "DELETE",
      "UpstreamPathTemplate": "/newapi/reset",
      "UpstreamHttpMethod": [
        "Get"
      ],
      "ServiceName": "core-app-discover-a"
    }, 
    {
      "Key": "api1",
      "DownstreamPathTemplate": "/test/list",
      "DownstreamScheme": "http",
      "UpstreamPathTemplate": "/newapi/list1",
      "UpstreamHttpMethod": [
        "Get"
      ],
      "ServiceName": "core-app-discover-a"
    },
    {
      "Key": "api2",
      "DownstreamPathTemplate": "/test/list",
      "DownstreamScheme": "http",
      "UpstreamPathTemplate": "/newapi/list2",
      "UpstreamHttpMethod": [
        "Get"
      ],
      "ServiceName": "core-app-discover-a"
    }
  ],
  "Aggregates": [
    {
      "RouteKeys": [
        "api1",
        "api2"
      ],
      "UpstreamPathTemplate": "/newapi/listall"
    }
  ],
  "GlobalConfiguration": {
    "BaseUrl": "http://0.0.0.0:20001",
    "ServiceDiscoveryProvider": {
      "Scheme": "http",
      "Host": "192.168.1.115",
      "Port": 8500,
      "Type": "PollConsul",
      "PollingInterval": 100
    },
    "QoSOptions": {
      "ExceptionsAllowedBeforeBreaking": 0,
      "DurationOfBreak": 0,
      "TimeoutValue": 0
    },
    "LoadBalancerOptions": {
      "Type": "LeastConnection",
      "Key": null,
      "Expiry": 0
    },
    "DownstreamScheme": "http",
    "HttpHandlerOptions": {
      "AllowAutoRedirect": false,
      "UseCookieContainer": false,
      "UseTracing": false
    }
  }
}

上述的ApiGateway一樣用DockerFile把專案包成Image

整合測試

docker-compose up -d –force-recreate

會看到一次起來這麼多服務

http://localhost:20001/newapi/get(透過api gateway打到downstream的service)

這邊多請求幾次會發現machineName一直在webapp1~3跳來跑去，採用load-balance的機制，ocelot會採用你設定的策略進行請求分派

ApiGateway有Aggregation的功能，就是可以把多個Api請求Combine在一起，讓請求變成1次，減少頻寬的消耗，這邊我也做了配置，來試看看吧

出於Ocelot.json的設定檔段落：

透過api gateway的組合讓 多個 Api可以一次 回傳

最後，打了很多次請求後，來總覽一下所有的請求摘要(程式是自已另外撈Redis的Request記錄來統計)

http://localhost:20001/newapi/list(透過api gateway打到down stream的service)

嘗試Docker Stop某一台 Discover-a1的服務，Consul DashBoard馬上就看的到紅點了！

這個時候再去打 之前load-balance的端點http://localhost:20001/newapi/get，會發現machineName會避開stop掉的服務只剩下 webapp1跟webapp3在輪循，因此做到了後端服務品質的保護

小插曲

ID不小心用成了Guid.New，所以會導致重新啟動就又拿到新的ID，造成了多一個Instance。但舊的也活了，因為他們的HealthCheck是一樣的

其實ApiGateway的議題，從Infra的角度上，可以玩的東西還有很多。

像是他也支援RateLimiting, QualityOfService(Polly) , 服務聚合(Aggregation)等機制，都可以從他們的官方文件看到設定方式，算是配置上不算太複雜。

不過 Ocelot在.net這邊發展一陣子後，近一年好像停更了！取而代之的好像是其他語言寫的更強的Apigateway: Envoy。

Envoy資源
https://www.envoyproxy.io/docs/envoy/latest/intro/what_is_envoy
https://www.netfos.com.tw/Projects/netfos/pages/solution/plan/20210111_plan.html

若只是要輕量級的，或是想參考其架構設計的，倒是可以翻github出來看看~

Github∶ https://github.com/ThreeMammals/Ocelot

這次Lab程式碼

若要拿去玩的，請把Ip, Password自行調整一下

一些文章的參考

https://ocelot.readthedocs.io/en/latest/features/servicediscovery.html?highlight=ServiceDiscoveryProvider

https://ocelot.readthedocs.io/en/latest/features/servicediscovery.html?highlight=ServiceDiscoveryProvider#

https://www.uj5u.com/net/232249.html

ASP.NET Core中Ocelot的使用：基于服务发现的负载均衡