Closes Stream C per docs/v2/implementation/phase-6-1-resilience-and-observability.md.
Core.Observability (new namespace):
- DriverHealthReport — pure-function aggregation over DriverHealthSnapshot list.
Empty fleet = Healthy. Any Faulted = Faulted. Any Unknown/Initializing (no
Faulted) = NotReady. Any Degraded or Reconnecting (no Faulted, no NotReady)
= Degraded. Else Healthy. HttpStatus(verdict) maps to the Stream C.1 state
matrix: Healthy/Degraded → 200, NotReady/Faulted → 503.
- LogContextEnricher — Serilog LogContext wrapper. Push(id, type, capability,
correlationId) returns an IDisposable scope; inner log calls carry
DriverInstanceId / DriverType / CapabilityName / CorrelationId structured
properties automatically. NewCorrelationId = 12-hex-char GUID slice for
cases where no OPC UA RequestHeader.RequestHandle is in flight.
CapabilityInvoker — now threads LogContextEnricher around every ExecuteAsync /
ExecuteWriteAsync call site. OtOpcUaServer passes driver.DriverType through
so logs correlate to the driver type too. Every capability call emits
structured fields per the Stream C.4 compliance check.
Server.Observability:
- HealthEndpointsHost — standalone HttpListener on http://localhost:4841/
(loopback avoids Windows URL-ACL elevation; remote probing via reverse
proxy or explicit netsh urlacl grant). Routes:
/healthz → 200 when (configDbReachable OR usingStaleConfig); 503 otherwise.
Body: status, uptimeSeconds, configDbReachable, usingStaleConfig.
/readyz → DriverHealthReport.Aggregate + HttpStatus mapping.
Body: verdict, drivers[], degradedDrivers[], uptimeSeconds.
anything else → 404.
Disposal cooperative with the HttpListener shutdown.
- OpcUaApplicationHost starts the health host after the OPC UA server comes up
and disposes it on shutdown. New OpcUaServerOptions knobs:
HealthEndpointsEnabled (default true), HealthEndpointsPrefix (default
http://localhost:4841/).
Program.cs:
- Serilog pipeline adds Enrich.FromLogContext + opt-in JSON file sink via
`Serilog:WriteJson = true` appsetting. Uses Serilog.Formatting.Compact's
CompactJsonFormatter (one JSON object per line — SIEMs like Splunk,
Datadog, Graylog ingest without a regex parser).
Server.Tests:
- Existing 3 OpcUaApplicationHost integration tests now set
HealthEndpointsEnabled=false to avoid port :4841 collisions under parallel
execution.
- New HealthEndpointsHostTests (9): /healthz healthy empty fleet; stale-config
returns 200 with flag; unreachable+no-cache returns 503; /readyz empty/
Healthy/Faulted/Degraded/Initializing drivers return correct status and
bodies; unknown path → 404. Uses ephemeral ports via Interlocked counter.
Core.Tests:
- DriverHealthReportTests (8): empty fleet, all-healthy, any-Faulted trumps,
any-NotReady without Faulted, Degraded without Faulted/NotReady, HttpStatus
per-verdict theory.
- LogContextEnricherTests (8): all 4 properties attach; scope disposes cleanly;
NewCorrelationId shape; null/whitespace driverInstanceId throws.
- CapabilityInvokerEnrichmentTests (2): inner logs carry structured
properties; no context leak outside the call site.
Full solution dotnet test: 1016 passing (baseline 906, +110 for Phase 6.1 so
far across Streams A+B+C). Pre-existing Client.CLI Subscribe flake unchanged.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Polling chosen over event-driven for initial scope: simpler, matches Admin UI consumer cadence, avoids DriverHost lifecycle-event plumbing that doesn't exist today. Event-driven push for sub-heartbeat latency is a straightforward follow-up.
Admin.Services.HostStatusService left-joins DriverHostStatus against ClusterNode on NodeId so rows persist even when the ClusterNode entry doesn't exist yet (first-boot bootstrap case). StaleThreshold = 30s — covers one missed publisher heartbeat plus a generous buffer for clock skew and GC pauses. Admin Components/Pages/Hosts.razor — FleetAdmin-visible page grouped by cluster (handles the '(unassigned)' case for rows without a matching ClusterNode). Four summary cards (Hosts / Running / Stale / Faulted); per-cluster table with Node / Driver / Host / State + Stale-badge / Last-transition / Last-seen / Detail columns; 10s auto-refresh via IServiceScopeFactory timer pattern matching FleetStatusPoller + Fleet dashboard (PR 27). Row-class highlighting: Faulted → table-danger, Stale → table-warning, else default. State badge maps DriverHostState enum to bootstrap color classes. Sidebar link added between 'Fleet status' and 'Clusters'.
Server csproj adds Microsoft.EntityFrameworkCore.SqlServer 10.0.0 + registers OtOpcUaConfigDbContext in Program.cs scoped via NodeOptions.ConfigDbConnectionString (no Admin-style manual SQL raw — the DbContext is the only access path, keeps migrations owner-of-record).
Tests — HostStatusPublisherTests (4 new Integration cases, uses per-run throwaway DB matching the FleetStatusPollerTests pattern): publisher upserts one row per host from each probe-capable driver and skips non-probe drivers; second tick advances LastSeenUtc without creating duplicate rows (upsert pattern verified end-to-end); state change between ticks updates State AND StateChangedUtc (datetime2(3) rounds to millisecond precision so comparison uses 1ms tolerance — documented inline); MapState translates every HostState enum member. Server.Tests Integration: 4 new tests pass. Admin build clean, Admin.Tests Unit still 23 / 0. docs/v2/lmx-followups.md item #7 marked DONE with three explicit deferred items (event-driven push, failure-count column, SignalR fan-out).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
