feat(scadabridge): wire AddZbTelemetry + /metrics in both composition roots

src/ZB.MOM.WW.ScadaBridge.Host/Program.cs

@@ -21,6 +21,7 @@ using ZB.MOM.WW.ScadaBridge.Security;
 using ZB.MOM.WW.ScadaBridge.SiteCallAudit;
 using ZB.MOM.WW.ScadaBridge.TemplateEngine;
 using ZB.MOM.WW.ScadaBridge.Transport;
+using ZB.MOM.WW.Telemetry;
 using Serilog;
 
 // SCADABRIDGE_CONFIG determines which role-specific config to load (Central or Site)
@@ -248,6 +249,12 @@ try
         // All three are anonymous and use the canonical ZbHealthWriter JSON output.
         app.MapZbHealth();
 
+        // Observability — mount the always-on Prometheus /metrics scrape endpoint.
+        // AddZbTelemetry (in SiteServiceRegistration.BindSharedOptions) wires the OTel
+        // Resource + standard instrumentation + Prometheus exporter; this exposes them.
+        // Requires endpoint routing (app.UseRouting() above).
+        app.MapZbMetrics();
+
         app.MapStaticAssets();
         app.MapCentralUI<ZB.MOM.WW.ScadaBridge.Host.Components.App>();
         app.MapInboundAPI();
@@ -304,6 +311,17 @@ try
 
         var app = builder.Build();
 
+        // Endpoint routing middleware. The gRPC service mapping below and the
+        // /metrics scrape endpoint both run on endpoint routing, so UseRouting()
+        // must be present before the Map* calls on the site role.
+        app.UseRouting();
+
+        // Observability — mount the always-on Prometheus /metrics scrape endpoint.
+        // AddZbTelemetry (in SiteServiceRegistration.Configure → BindSharedOptions)
+        // wires the OTel Resource + standard instrumentation + Prometheus exporter;
+        // this exposes them on the site node too.
+        app.MapZbMetrics();
+
         // Map gRPC service — resolves the singleton SiteStreamGrpcServer from DI
         app.MapGrpcService<ZB.MOM.WW.ScadaBridge.Communication.Grpc.SiteStreamGrpcServer>();
 

src/ZB.MOM.WW.ScadaBridge.Host/SiteServiceRegistration.cs

@@ -11,6 +11,7 @@ using ZB.MOM.WW.ScadaBridge.NotificationService;
 using ZB.MOM.WW.ScadaBridge.SiteEventLogging;
 using ZB.MOM.WW.ScadaBridge.SiteRuntime;
 using ZB.MOM.WW.ScadaBridge.StoreAndForward;
+using ZB.MOM.WW.Telemetry;
 
 namespace ZB.MOM.WW.ScadaBridge.Host;
 
@@ -114,5 +115,19 @@ public static class SiteServiceRegistration
         // writers so they can stamp the SourceNode column. Registered here in
         // shared bootstrap because every node (central + site) needs it.
         services.AddSingleton<INodeIdentityProvider, NodeIdentityProvider>();
+
+        // Observability — shared ZB.MOM.WW.Telemetry. Registered in shared bootstrap so
+        // BOTH the central and site composition roots wire the OTel Resource (the
+        // service.name/site.id/node.role identity triple) + standard instrumentation +
+        // the always-on Prometheus exporter. Mount the /metrics scrape endpoint per role
+        // with app.MapZbMetrics(). The same `?? "central"` SiteId default Program.cs uses
+        // is applied here so the Resource attribute matches the log-enricher value.
+        // Meters left empty — application instruments are a deferred follow-on.
+        services.AddZbTelemetry(o =>
+        {
+            o.ServiceName = "scadabridge";
+            o.SiteId = config["ScadaBridge:Node:SiteId"] ?? "central";
+            o.NodeRole = config["ScadaBridge:Node:Role"];
+        });
     }
 }

tests/ZB.MOM.WW.ScadaBridge.Host.Tests/MetricsEndpointTests.cs

@@ -0,0 +1,79 @@
+using System.Net;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.Extensions.Configuration;
+
+namespace ZB.MOM.WW.ScadaBridge.Host.Tests;
+
+/// <summary>
+/// Observability adoption: verifies the shared ZB.MOM.WW.Telemetry Prometheus
+/// scrape endpoint (<c>/metrics</c>, mounted by <c>app.MapZbMetrics()</c>) is wired into the
+/// Central composition root. <c>AddZbTelemetry</c> (registered in
+/// <see cref="SiteServiceRegistration.BindSharedOptions"/>) always wires the Prometheus
+/// exporter, so the endpoint returns the Prometheus exposition format regardless of DB /
+/// cluster state. This is a pure route assertion — it requires no database, LDAP, or formed
+/// Akka cluster. The Central-role factory bootstrap mirrors <see cref="HealthCheckTests"/>.
+/// </summary>
+public class MetricsEndpointTests : IDisposable
+{
+    private readonly List<IDisposable> _disposables = new();
+
+    public MetricsEndpointTests()
+    {
+        // Host-003: connection strings are externalised; supply them via env vars.
+        _disposables.Add(new CentralDbTestEnvironment());
+    }
+
+    public void Dispose()
+    {
+        foreach (var d in _disposables)
+        {
+            try { d.Dispose(); } catch { /* best effort */ }
+        }
+    }
+
+    private WebApplicationFactory<Program> CreateCentralFactory()
+    {
+        var factory = new WebApplicationFactory<Program>()
+            .WithWebHostBuilder(builder =>
+            {
+                builder.ConfigureAppConfiguration((context, config) =>
+                {
+                    config.AddInMemoryCollection(new Dictionary<string, string?>
+                    {
+                        ["ScadaBridge:Node:NodeHostname"] = "localhost",
+                        ["ScadaBridge:Node:RemotingPort"] = "0",
+                        ["ScadaBridge:Cluster:SeedNodes:0"] = "akka.tcp://scadabridge@localhost:2551",
+                        ["ScadaBridge:Cluster:SeedNodes:1"] = "akka.tcp://scadabridge@localhost:2552",
+                        ["ScadaBridge:Database:SkipMigrations"] = "true",
+                    });
+                });
+                builder.UseSetting("ScadaBridge:Node:Role", "Central");
+                builder.UseSetting("ScadaBridge:Database:SkipMigrations", "true");
+            });
+        _disposables.Add(factory);
+        return factory;
+    }
+
+    [Fact]
+    public async Task Metrics_Endpoint_IsMapped()
+    {
+        var previousEnv = Environment.GetEnvironmentVariable("DOTNET_ENVIRONMENT");
+        try
+        {
+            Environment.SetEnvironmentVariable("DOTNET_ENVIRONMENT", "Central");
+            var factory = CreateCentralFactory();
+            var client = factory.CreateClient();
+            _disposables.Add(client);
+
+            var response = await client.GetAsync("/metrics");
+
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            var body = await response.Content.ReadAsStringAsync();
+            Assert.Contains("# ", body); // Prometheus exposition (HELP/TYPE comments)
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("DOTNET_ENVIRONMENT", previousEnv);
+        }
+    }
+}