Service Discovery (Consul) in ASP .NET Core API with Ocelot Gateway

Service Discovery (Consul) in ASP .NET Core API with Ocelot Gateway.

This article will show how to setup API Gateway using Ocelot.Net and Consul.

Step 1

• Set up the Consul Service in Windows, From the below link "https://developer.hashicorp.com/consul/downloads" (Click Here for Download).
• Place in a Directory, open the command prompt, and type the below command to start the development server agent "consul agent -dev".
• Open the Browser and type the following URL "http://127.0.0.1:8500/". If the console UI opens, we set up the Consul properly. 

Step 2

In C# Rest Services (Each service needs to be configured like below).

Install Nuget Packages,

• Consul
• Ocelot.Provider.Consul (Gateway Service)

Inject like this in all services (we need to configure service discovery)

services.AddSingleton<IConsulClient, ConsulClient>(p => new ConsulClient(consulConfig =>
{
    consulConfig.Address = new Uri("http://127.0.0.1:8500");
}));

Using the Consul,

public static IApplicationBuilder UseConsul(this IApplicationBuilder app)
{

    var consulClient = app.ApplicationServices.GetRequiredService<IConsulClient>();
    var lifetime = app.ApplicationServices.GetRequiredService<IApplicationLifetime>();
    var settings = app.ApplicationServices.GetRequiredService<ConfigurationMaster>();


    if (!(app.Properties["server.Features"] is FeatureCollection features))
    {
        return app;
    } 
     
    var serviceName = settings.ServiceDiscoveryConfig.NameOfService;
    var serviceId = settings.ServiceDiscoveryConfig.IdOfService;
    var uri = new Uri($"http://{settings.ServiceDiscoveryConfig.Host}");

    var registration = new AgentServiceRegistration()
    {
        ID = serviceId,
        Name = serviceName,
        Address = $"localhost",
        Port = uri.Port,
        Tags = new[] { $"urlprefix-/{settings.ServiceDiscoveryConfig.IdOfService}" }
    };

   var result= consulClient.Agent.ServiceDeregister(registration.ID).Result;
    result = consulClient.Agent.ServiceRegister(registration).Result;

    lifetime.ApplicationStopping.Register(() =>
    {
        consulClient.Agent.ServiceDeregister(registration.ID).Wait();
    });

    return app;
}

Update App Settings (JSON) File:

"ServiceDiscoveryConfig": {
  "Host": "localhost:7201",
  "Port": {Hosted Service Port},
  "NameOfService": "{Service Name Unique}",
  "IdOfService": "{Service ID Our Wish}"
}

Update the Gateway Settings File as Follow in (GlobalConfiguration):

"ServiceDiscoveryProvider": {
  "Host": "localhost",
  "Port": 8500,
  "Type": "PollConsul",
  "PollingInterval": 100
  //"Type": "Consul" - Each Request it will update information
  /*
    Type
      Consul, means that Ocelot will get service information from consul per request
      PollConsul, means that Ocelot will poll Consul for latest service information
  */
}

Sample Gateway End Point Configuration:

{
  "Routes": [
    {
      "UseServiceDiscovery": true,
      "DownstreamPathTemplate": "/v1/{everything}",
      "DownstreamScheme": "http",
      "ServiceName": "Sample API",
      "UpstreamPathTemplate": "/v1/{everything}",
      "UpstreamHttpMethod": [ "GET" ],
      "Priority": 1,
      "ReRoutesCaseSensitive": false,
      "LoadBalancerOptions": {
        "Type": "LeastConnection"
      }
    },
    {
      "DownstreamPathTemplate": "/v1/{everything}",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 7201
        }
      ],
      "UpstreamPathTemplate": "/api/v2/{everything}",
      "UpstreamHttpMethod": [ "GET", "POST" ],
      "Priority": 1
    }
  ],
  "GlobalConfiguration": {
    "BaseUrl": "https://localhost:7123",
    "ServiceDiscoveryProvider": {
      "Host": "localhost",
      "Port": 8500,
      "Type": "PollConsul",
      "PollingInterval": 100
      //"Type": "Consul" - Each Request it will update information
      /*
        Type
          Consul, means that Ocelot will get service information from consul per request
          PollConsul, means that Ocelot will poll Consul for latest service information
      */
    }
  }
}