scadalink-design/deprecated/lmxproxy/docs/requirements/Component-HealthAndMetrics.md

Component: HealthAndMetrics

Purpose

Provides health checking, performance metrics collection, and an HTTP status dashboard for monitoring the LmxProxy service.

Location

• src/ZB.MOM.WW.LmxProxy.Host/Health/HealthCheckService.cs — basic health check.
• src/ZB.MOM.WW.LmxProxy.Host/Health/DetailedHealthCheckService.cs — detailed health check with test tag read.
• src/ZB.MOM.WW.LmxProxy.Host/Metrics/PerformanceMetrics.cs — operation metrics collection.
• src/ZB.MOM.WW.LmxProxy.Host/Status/StatusReportService.cs — status report generation.
• src/ZB.MOM.WW.LmxProxy.Host/Status/StatusWebServer.cs — HTTP status endpoint.

Responsibilities

• Evaluate service health based on connection state, operation success rates, and test tag reads.
• Track per-operation performance metrics (counts, latencies, percentiles).
• Serve an HTML status dashboard and JSON/health HTTP endpoints.
• Report metrics to logs on a periodic interval.

1. Health Checks

1.1 Basic Health Check (HealthCheckService)

CheckHealthAsync() evaluates:

Check	Healthy	Degraded
MxAccess connected	Yes	—
Success rate (if > 100 total ops)	≥ 50%	< 50%
Client count	≤ 100	> 100

Returns health data dictionary: scada_connected, scada_connection_state, total_clients, total_tags, total_operations, average_success_rate.

1.2 Detailed Health Check (DetailedHealthCheckService)

CheckHealthAsync() performs an active probe:

1. Checks IsConnected — returns Unhealthy if not connected.
2. Reads a test tag (default System.Heartbeat).
3. If test tag quality is not Good — returns Degraded.
4. If test tag timestamp is older than 5 minutes — returns Degraded (stale data detection).
5. Otherwise returns Healthy.

2. Performance Metrics

2.1 Tracking

PerformanceMetrics uses a ConcurrentDictionary<string, OperationMetrics> to track operations by name.

Operations tracked: Read, ReadBatch, Write, WriteBatch (recorded by ScadaGrpcService).

2.2 Recording

Two recording patterns:

• RecordOperation(name, duration, success) — explicit recording.
• BeginOperation(name) — returns an ITimingScope (disposable). On dispose, automatically records duration (via Stopwatch) and success flag (set via SetSuccess(bool)).

2.3 Per-Operation Statistics

OperationMetrics maintains:

• _totalCount, _successCount — running counters.
• _totalMilliseconds, _minMilliseconds, _maxMilliseconds — latency range.
• _durations — rolling buffer of up to 1000 latency samples for percentile calculation.

MetricsStatistics snapshot:

• TotalCount, SuccessCount, SuccessRate (percentage).
• AverageMilliseconds, MinMilliseconds, MaxMilliseconds.
• Percentile95Milliseconds — calculated from sorted samples at the 95th percentile index.

2.4 Periodic Reporting

A timer fires every 60 seconds, logging a summary of all operation metrics to Serilog.

3. Status Web Server

3.1 Server

StatusWebServer uses HttpListener on http://+:{Port}/ (default port 8080).

• Starts an async request-handling loop, spawning a task per request.
• Graceful shutdown: cancels the listener, waits 5 seconds for the listener task to exit.
• Returns HTTP 405 for non-GET methods, HTTP 500 on errors.

3.2 Endpoints

Endpoint	Method	Response
/	GET	HTML dashboard (auto-refresh every 30 seconds)
/api/status	GET	JSON status report (camelCase)
/api/health	GET	Plain text OK (200) or UNHEALTHY (503)

3.3 HTML Dashboard

Generated by StatusReportService:

• Bootstrap-like CSS grid layout with status cards.
• Color-coded status: green = Healthy, yellow = Degraded, red = Unhealthy/Error.
• Operations table with columns: Count, SuccessRate, Avg/Min/Max/P95 milliseconds.
• Service metadata: ServiceName, Version (assembly version), connection state.
• Subscription stats: TotalClients, TotalTags, ActiveSubscriptions.
• Auto-refresh via <meta http-equiv="refresh" content="30">.
• Last updated timestamp.

3.4 JSON Status Report

Fully nested structure with camelCase property names:

• Service metadata, connection status, subscription stats, performance data, health check results.

Dependencies

• MxAccessClient — IsConnected, ConnectionState for health checks; test tag read for detailed check.
• SubscriptionManager — subscription statistics.
• PerformanceMetrics — operation statistics for status report and health evaluation.
• Configuration — WebServerConfiguration for port and prefix.

Interactions

• GrpcServer populates PerformanceMetrics via timing scopes on every RPC.
• ServiceHost creates all health/metrics/status components at startup and disposes them at shutdown.
• External monitoring systems can poll /api/health for availability checks.