Handle registration client failures gracefully

HealthMonitoring/HealthMonitoring.Client/HealthMonitoringRegistrationClient.cs

@@ -28,9 +28,9 @@ public sealed record ServiceRegistrationResult(string ServiceId, string Action,
 
 public interface IHealthMonitoringRegistrationClient
 {
-    Task<ServiceRegistrationResult> RegisterAsync(ServiceRegistrationOptions options, CancellationToken cancellationToken = default);
+    Task<ServiceRegistrationResult?> RegisterAsync(ServiceRegistrationOptions options, CancellationToken cancellationToken = default);
     Task SetDependencyMappingsAsync(string serviceId, IEnumerable<DependencyMappingOptions> mappings, CancellationToken cancellationToken = default);
-    Task<ServiceRegistrationResult> RegisterAndConfigureAsync(ServiceRegistrationOptions options, IEnumerable<DependencyMappingOptions> mappings, CancellationToken cancellationToken = default);
+    Task<ServiceRegistrationResult?> RegisterAndConfigureAsync(ServiceRegistrationOptions options, IEnumerable<DependencyMappingOptions> mappings, CancellationToken cancellationToken = default);
 }
 
 public sealed class HealthMonitoringRegistrationClient(
@@ -39,7 +39,7 @@ public sealed class HealthMonitoringRegistrationClient(
 {
     private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web);
 
-    public async Task<ServiceRegistrationResult> RegisterAsync(ServiceRegistrationOptions options, CancellationToken cancellationToken = default)
+    public async Task<ServiceRegistrationResult?> RegisterAsync(ServiceRegistrationOptions options, CancellationToken cancellationToken = default)
     {
         ArgumentNullException.ThrowIfNull(options);
         var monitorType = ParseMonitorType(options.MonitorType);
@@ -71,12 +71,20 @@ public async Task<ServiceRegistrationResult> RegisterAsync(ServiceRegistrationOp
             "POST /api/services/register body: {RequestBody}",
             JsonSerializer.Serialize(loggedPayload, JsonOptions));
 
-        using var response = await httpClient.PostAsJsonAsync("api/services/register", payload, JsonOptions, cancellationToken);
+        try
+        {
+            using var response = await httpClient.PostAsJsonAsync("api/services/register", payload, JsonOptions, cancellationToken);
 
-        await EnsureSuccessAsync(response, "register service", cancellationToken);
-        var result = await response.Content.ReadFromJsonAsync<ServiceRegistrationResponsePayload>(JsonOptions, cancellationToken)
-            ?? throw new InvalidOperationException("The monitoring server returned an empty registration response.");
-        return new ServiceRegistrationResult(result.ServiceId, result.Action, result.Service.Id);
+            await EnsureSuccessAsync(response, "register service", cancellationToken);
+            var result = await response.Content.ReadFromJsonAsync<ServiceRegistrationResponsePayload>(JsonOptions, cancellationToken)
+                ?? throw new InvalidOperationException("The monitoring server returned an empty registration response.");
+            return new ServiceRegistrationResult(result.ServiceId, result.Action, result.Service.Id);
+        }
+        catch (Exception exception) when (!cancellationToken.IsCancellationRequested)
+        {
+            logger?.LogWarning(exception, "Unable to register service '{ServiceId}' with health monitoring.", options.ServiceId);
+            return null;
+        }
     }
 
     public async Task SetDependencyMappingsAsync(string serviceId, IEnumerable<DependencyMappingOptions> mappings, CancellationToken cancellationToken = default)
@@ -100,9 +108,10 @@ public async Task SetDependencyMappingsAsync(string serviceId, IEnumerable<Depen
         }
     }
 
-    public async Task<ServiceRegistrationResult> RegisterAndConfigureAsync(ServiceRegistrationOptions options, IEnumerable<DependencyMappingOptions> mappings, CancellationToken cancellationToken = default)
+    public async Task<ServiceRegistrationResult?> RegisterAndConfigureAsync(ServiceRegistrationOptions options, IEnumerable<DependencyMappingOptions> mappings, CancellationToken cancellationToken = default)
     {
         var result = await RegisterAsync(options, cancellationToken);
+        if (result is null) return null;
         await SetDependencyMappingsAsync(options.ServiceId, mappings, cancellationToken);
         return result;
     }

HealthMonitoring/HealthMonitoring.Tests/Client/HealthMonitoringRegistrationClientTests.cs

@@ -38,6 +38,7 @@ public async Task RegisterAsync_posts_service_configuration_and_returns_acknowle
             Version = "1.2.3"
         });
 
+        Assert.NotNull(result);
         Assert.Equal("created", result.Action);
         Assert.Equal(Guid.Parse("11111111-1111-1111-1111-111111111111"), result.MonitoredServiceId);
         Assert.Equal(HttpMethod.Post, handler.Request!.Method);
@@ -81,6 +82,29 @@ await client.RegisterAsync(new ServiceRegistrationOptions
         Assert.DoesNotContain("super-secret", logger.Messages.Single());
     }
 
+    [Fact]
+    public async Task RegisterAsync_returns_null_and_logs_when_registration_call_fails()
+    {
+        var handler = new RecordingHandler(_ => new HttpResponseMessage(HttpStatusCode.ServiceUnavailable)
+        {
+            Content = new StringContent("monitoring unavailable")
+        });
+        var logger = new RecordingLogger<HealthMonitoringRegistrationClient>();
+        var client = new HealthMonitoringRegistrationClient(
+            new HttpClient(handler) { BaseAddress = new Uri(MonitoringBaseUrl) },
+            logger);
+
+        var result = await client.RegisterAsync(new ServiceRegistrationOptions
+        {
+            ServiceId = PaymentsApiServiceId,
+            Name = "Payments API",
+            HealthUrl = new Uri("https://payments-api/health")
+        });
+
+        Assert.Null(result);
+        Assert.Contains(logger.Messages, message => message.Contains("register service", StringComparison.OrdinalIgnoreCase));
+    }
+
     [Fact]
     public async Task SetDependencyMappingsAsync_resolves_target_service_and_upserts_mapping()
     {

HealthMonitoring/HealthMonitoring.Tests/Client/HealthMonitoringRegistrationExtensionsTests.cs

@@ -82,7 +82,7 @@ private sealed class RecordingRegistrationClient : IHealthMonitoringRegistration
         public ServiceRegistrationOptions? Service { get; private set; }
         public IEnumerable<DependencyMappingOptions>? Dependencies { get; private set; }
 
-        public Task<ServiceRegistrationResult> RegisterAsync(ServiceRegistrationOptions options, CancellationToken cancellationToken = default)
+        public Task<ServiceRegistrationResult?> RegisterAsync(ServiceRegistrationOptions options, CancellationToken cancellationToken = default)
         {
             cancellationToken.ThrowIfCancellationRequested();
             throw new NotSupportedException($"RegisterAsync is not used for {options.ServiceId}.");
@@ -94,12 +94,12 @@ public Task SetDependencyMappingsAsync(string serviceId, IEnumerable<DependencyM
             throw new NotSupportedException($"SetDependencyMappingsAsync is not used for {serviceId} with {mappings.Count()} mappings.");
         }
 
-        public Task<ServiceRegistrationResult> RegisterAndConfigureAsync(ServiceRegistrationOptions options, IEnumerable<DependencyMappingOptions> mappings, CancellationToken cancellationToken = default)
+        public Task<ServiceRegistrationResult?> RegisterAndConfigureAsync(ServiceRegistrationOptions options, IEnumerable<DependencyMappingOptions> mappings, CancellationToken cancellationToken = default)
         {
             cancellationToken.ThrowIfCancellationRequested();
             Service = options;
             Dependencies = mappings;
-            return Task.FromResult(new ServiceRegistrationResult(options.ServiceId, "created", Guid.NewGuid()));
+            return Task.FromResult<ServiceRegistrationResult?>(new ServiceRegistrationResult(options.ServiceId, "created", Guid.NewGuid()));
         }
     }
 }