Added 'WatchKube' discovery provider

Author: VIMPELCOM_MAIN\NKuksov

src/Ocelot.Provider.Kubernetes/EndPointClientV1.cs

@@ -7,21 +7,24 @@ namespace Ocelot.Provider.Kubernetes
 {
     public class EndPointClientV1 : KubeResourceClient, IEndPointClient
     {
-        private readonly HttpRequest _collection;
+        private readonly HttpRequest _byName;
+        private readonly HttpRequest _watchByName;
 
         public EndPointClientV1(IKubeApiClient client) : base(client)
         {
-            _collection = KubeRequest.Create("api/v1/namespaces/{Namespace}/endpoints/{ServiceName}");
+            _byName = KubeRequest.Create("api/v1/namespaces/{Namespace}/endpoints/{ServiceName}");
+            _watchByName = KubeRequest.Create("api/v1/watch/namespaces/{Namespace}/endpoints/{ServiceName}");
         }
 
-        public async Task<EndpointsV1> GetAsync(string serviceName, string kubeNamespace = null, CancellationToken cancellationToken = default)
+        public async Task<EndpointsV1> GetAsync(string serviceName, string kubeNamespace = null,
+            CancellationToken cancellationToken = default)
         {
             if (string.IsNullOrEmpty(serviceName))
             {
                 throw new ArgumentNullException(nameof(serviceName));
             }
 
-            var request = _collection
+            var request = _byName
                 .WithTemplateParameters(new
                 {
                     Namespace = kubeNamespace ?? KubeClient.DefaultNamespace,
@@ -34,5 +37,23 @@ public async Task<EndpointsV1> GetAsync(string serviceName, string kubeNamespace
                 ? await response.ReadContentAsAsync<EndpointsV1>()
                 : null;
         }
+
+        public IObservable<IResourceEventV1<EndpointsV1>> Watch(string serviceName, string kubeNamespace,
+            CancellationToken cancellationToken = default)
+        {
+            if (string.IsNullOrEmpty(serviceName))
+            {
+                throw new ArgumentNullException(nameof(serviceName));
+            }
+
+            return ObserveEvents<EndpointsV1>(
+                _watchByName.WithTemplateParameters(new
+                {
+                    ServiceName = serviceName,
+                    Namespace = kubeNamespace ?? KubeClient.DefaultNamespace,
+                }),
+                "watch v1/Endpoints '" + serviceName + "' in namespace " +
+                (kubeNamespace ?? KubeClient.DefaultNamespace));
+        }
     }
 }

src/Ocelot.Provider.Kubernetes/Interfaces/IEndPointClient.cs

@@ -6,4 +6,6 @@ namespace Ocelot.Provider.Kubernetes.Interfaces;
 public interface IEndPointClient : IKubeResourceClient
 {
     Task<EndpointsV1> GetAsync(string serviceName, string kubeNamespace = null, CancellationToken cancellationToken = default);
+
+    IObservable<IResourceEventV1<EndpointsV1>> Watch(string serviceName, string kubeNamespace = null, CancellationToken cancellationToken = default);
 }

src/Ocelot.Provider.Kubernetes/Kube.cs

@@ -47,7 +47,7 @@ public virtual async Task<List<Service>> GetAsync()
     }
 
     private Task<EndpointsV1> GetEndpoint() => _kubeApi
-        .ResourceClient(client => new EndPointClientV1(client))
+        .EndpointsV1()
         .GetAsync(_configuration.KeyOfServiceInK8s, _configuration.KubeNamespace);
 
     private bool CheckErroneousState(EndpointsV1 endpoint)

src/Ocelot.Provider.Kubernetes/KubeApiClientExtensions.cs

@@ -0,0 +1,9 @@
+using Ocelot.Provider.Kubernetes.Interfaces;
+
+namespace Ocelot.Provider.Kubernetes;
+
+public static class KubeApiClientExtensions
+{
+    public static IEndPointClient EndpointsV1(this IKubeApiClient client)
+        => client.ResourceClient(x => new EndPointClientV1(client));
+}

src/Ocelot.Provider.Kubernetes/KubernetesProviderFactory.cs

@@ -1,18 +1,20 @@
-using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection;
 using Ocelot.Configuration;
-using Ocelot.Logging;
+using Ocelot.Logging;
 using Ocelot.Provider.Kubernetes.Interfaces;
 
 namespace Ocelot.Provider.Kubernetes
 {
     public static class KubernetesProviderFactory
-    {
-        /// <summary>
-        /// String constant used for provider type definition.
+    {
+        /// <summary>
+        /// String constant used for provider type definition.
         /// </summary>
         public const string PollKube = nameof(Kubernetes.PollKube);
-
-        public static ServiceDiscoveryFinderDelegate Get { get; } = CreateProvider;
+
+        public const string WatchKube = nameof(Kubernetes.WatchKube);
+
+        public static ServiceDiscoveryFinderDelegate Get { get; } = CreateProvider;
 
         private static IServiceDiscoveryProvider CreateProvider(IServiceProvider provider, ServiceProviderConfiguration config, DownstreamRoute route)
         {
@@ -27,11 +29,16 @@ private static IServiceDiscoveryProvider CreateProvider(IServiceProvider provide
                 Scheme = route.DownstreamScheme,
             };
 
+            if (WatchKube.Equals(config.Type, StringComparison.OrdinalIgnoreCase))
+            {
+                return new WatchKube(configuration, factory, kubeClient, serviceBuilder);
+            }
+
             var defaultK8sProvider = new Kube(configuration, factory, kubeClient, serviceBuilder);
- 
-            return PollKube.Equals(config.Type, StringComparison.OrdinalIgnoreCase)
-                ? new PollKube(config.PollingInterval, factory, defaultK8sProvider)
-                : defaultK8sProvider;
+ 
+            return PollKube.Equals(config.Type, StringComparison.OrdinalIgnoreCase)
+                ? new PollKube(config.PollingInterval, factory, defaultK8sProvider)
+                : defaultK8sProvider;
         }
     }
 }

src/Ocelot.Provider.Kubernetes/WatchKube.cs

@@ -0,0 +1,78 @@
+using KubeClient.Models;
+using Ocelot.Logging;
+using Ocelot.Provider.Kubernetes.Interfaces;
+using Ocelot.Values;
+
+namespace Ocelot.Provider.Kubernetes;
+
+// Dispose() won't be called because provider wasn't resolved from DI
+public class WatchKube : IServiceDiscoveryProvider, IDisposable
+{
+    private readonly KubeRegistryConfiguration _configuration;
+    private readonly IOcelotLogger _logger;
+    private readonly IKubeApiClient _kubeApi;
+    private readonly IKubeServiceBuilder _serviceBuilder;
+    
+    private List<Service> _services = null;
+    private readonly IDisposable _subscription;
+
+    public WatchKube(
+        KubeRegistryConfiguration configuration,
+        IOcelotLoggerFactory factory,
+        IKubeApiClient kubeApi,
+        IKubeServiceBuilder serviceBuilder)
+    {
+        _configuration = configuration;
+        _logger = factory.CreateLogger<Kube>();
+        _kubeApi = kubeApi;
+        _serviceBuilder = serviceBuilder;
+        
+        _subscription = CreateSubscription();
+    }
+
+    public virtual async Task<List<Service>> GetAsync()
+    {
+        // need to wait for first result fetching somehow
+        if (_services is null)
+        {
+            await Task.Delay(1000);
+        }
+
+        if (_services is not { Count: > 0 })
+        {
+            _logger.LogWarning(() => GetMessage("Subscription to service endpoints gave no results!"));
+        }
+
+        return _services;
+    }
+
+    private IDisposable CreateSubscription() =>
+        _kubeApi
+            .EndpointsV1()
+            .Watch(_configuration.KeyOfServiceInK8s, _configuration.KubeNamespace)
+            .Subscribe(
+                onNext: endpointEvent =>
+                {
+                    _services = endpointEvent.EventType switch
+                    {
+                        ResourceEventType.Deleted or ResourceEventType.Error => new(),
+                        _ when (endpointEvent.Resource?.Subsets?.Count ?? 0) == 0 => new(),
+                        _ => _serviceBuilder.BuildServices(_configuration, endpointEvent.Resource).ToList(),
+                    };
+                },
+                onError: ex =>
+                {
+                    // recreate subscription in case of exceptions?
+                    _logger.LogError(() => GetMessage("Endpoints subscription error occured"), ex);
+                },
+                onCompleted: () =>
+                {
+                    // called only when subscription is cancelled
+                    _logger.LogWarning(() => GetMessage("Subscription to service endpoints completed"));
+                });
+
+    private string GetMessage(string message)
+        => $"{nameof(WatchKube)} provider. Namespace:{_configuration.KubeNamespace}, Service:{_configuration.KeyOfServiceInK8s}; {message}";
+
+    public void Dispose() => _subscription.Dispose();
+}