fix(GWC-37): grade the alarm subtag watch-list instead of latching it silently
The subtag fallback's coverage was fixed at SubscribeAlarms time and never re-examined. AlarmWatchListResolver deliberately swallows a Galaxy Repository outage and returns whatever configuration contributed, so a discovery failure at startup left the monitor subscribed with an empty watch-list for the rest of its life. In Auto mode the alarmmgr primary keeps working, so nothing looks wrong until the failover that needs the standby finds it covering zero alarms — with a single LogWarning emitted possibly weeks earlier as the only evidence. ResolveAsync now returns an AlarmWatchListResolution (targets + whether discovery was attempted and whether it failed, with the failure message), which is what the caller needed to tell "discovery produced nothing" from "nothing was configured". GatewayAlarmMonitor grades that resolution against the effective mode and folds the verdict into AlarmProviderStatus, so it reaches the feed, the dashboard badge and every late-joining subscriber: - zero targets while the mode can need them (Auto/ForceSubtag) -> degraded with SubtagWatchListEmpty; discovery enabled but failing adds SubtagDiscoveryFailed and the message. ForceAlarmManager builds no subtag consumer and is not graded. - degraded is now the OR of "subtag is serving" and "the watch-list covers nothing", so the Auto case where alarmmgr is healthy and the standby is empty is visible. DashboardAlarmProviderStatus renders that combination as the amber "Alarm Manager (no subtag standby)" badge rather than the failover label, which would have named the wrong live provider. - on the failover edge (ApplyProviderModeChangeAsync, toMode == Subtag) the monitor re-resolves BEFORE publishing the status and reports any difference as SubtagWatchListStale with both counts. The re-resolution is deliberately NOT re-sent. The worker rejects a second SubscribeAlarms while subscribed (AlarmCommandHandler.Subscribe), and the only expressible replacement — UnsubscribeAlarms then SubscribeAlarms — rebuilds FailoverAlarmConsumer, which restarts on the primary that just failed and discards the warm standby state, so it would flap the feed rather than repair it. The finding's other alternative (treat empty coverage as a lifecycle failure) was rejected too: it would crash-loop the monitor every 5 s on a persistent GR outage and take the working alarmmgr feed down with it. A monitor restart re-resolves and re-sends, and the status now says so. Docs: docs/AlarmClientDiscovery.md gains the grading rules and corrects two stale claims (the resolver method name, and "re-runs discovery on its reconcile cadence and pushes an updated watch-list", which never happened); gateway.md gains the standby-coverage visibility paragraph; docs/GatewayConfiguration.md records the consequence on the UseGalaxyRepository and Mode rows. Tests: SubtagCoverage_WhenDiscoveryFailsAtSubscribe_ProviderStatusIsDegradedWith- Reason and SubtagCoverage_WhenDiscoveryRecoversByFailover_ReResolvesAndReportsDrift drive the fake-worker monitor; two resolver cases pin the new provenance fields. The pre-existing dashboard case for degraded+ALARMMGR now asserts the new label.
This commit is contained in:
Joseph Doherty
@@ -57,6 +57,20 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
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private string _providerReason = string.Empty;
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private DateTimeOffset _providerSince = DateTimeOffset.UtcNow;
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// GWC-37 subtag-coverage verdict, guarded by _sync: whether the watch-list the worker is
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// using can actually cover anything, and why not. Independent of _providerDegraded (which
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// means "the subtag provider is the one serving"): in Auto mode the alarm manager can be
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// serving perfectly while the standby behind it covers zero alarms, and that is invisible
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// until the failover that needs it. Folded into BuildProviderStatus so it reaches the feed,
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// the dashboard badge and every late-joining subscriber rather than only a startup log line.
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private bool _subtagCoverageMissing;
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private string _subtagCoverageReason = string.Empty;
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// The watch-list references actually sent to the worker in SubscribeAlarms, guarded by _sync.
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// The worker holds that list for the life of the subscription, so a later re-resolution is
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// compared against this to report drift rather than silently diverging.
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private IReadOnlyCollection<string> _sentWatchListReferences = [];
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// Whether the worker's most recent reconcile fetch was capped, guarded by _sync.
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// Written only by ApplyReconcile (and cleared with the cache), so it describes the last full
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// reconcile — not necessarily the current _alarms contents, which live transitions keep moving
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@@ -329,12 +343,25 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
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private async Task SubscribeAlarmsAsync(string sessionId, string subscription, CancellationToken cancellationToken)
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{
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IReadOnlyList<AlarmSubtagTarget> watchList = await _watchListResolver
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AlarmWatchListResolution resolution = await _watchListResolver
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.ResolveAsync(_options, cancellationToken)
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.ConfigureAwait(false);
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IReadOnlyList<AlarmSubtagTarget> watchList = resolution.Targets;
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AlarmProviderMode forcedMode = MapForcedMode(_options.Fallback.Mode);
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// GWC-37: grade the coverage before the command goes out, so a Galaxy Repository outage at
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// startup is a standing status on the feed instead of one log line an operator reads weeks
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// later — when the failover that needed the watch-list finds it empty. Broadcast because
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// feed subscribers outlive the monitor's worker session and may already be attached.
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lock (_sync)
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{
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_sentWatchListReferences = watchList
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.Select(target => target.AlarmFullReference)
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.ToHashSet(StringComparer.OrdinalIgnoreCase);
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SetSubtagCoverage(GradeSubtagCoverage(forcedMode, resolution, staleAgainstSent: false), broadcast: true);
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}
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_logger.LogInformation(
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"Alarm subscribe: forcedMode={ForcedMode} configMode={ConfigMode} watchList={WatchListCount}.",
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forcedMode, _options.Fallback.Mode, watchList.Count);
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@@ -518,6 +545,20 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
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AlarmProviderMode toMode = change.Mode;
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string reason = change.Reason ?? string.Empty;
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// GWC-37: this is the moment the subtag watch-list stops being theoretical — the provider
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// that is about to serve is the one built from it. Re-resolve BEFORE the status is
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// published so the frame the operator sees on the failover carries the coverage verdict
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// rather than a second frame later, and so a watch-list that has drifted since
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// SubscribeAlarms is reported instead of silently diverging. The re-resolution is NOT
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// re-sent: the worker rejects a second SubscribeAlarms while subscribed, and the only way
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// to replace the list — Unsubscribe then Subscribe — rebuilds the FailoverAlarmConsumer,
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// which restarts on the primary that just failed and discards the warm standby state, so
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// it would flap the feed rather than repair it. A monitor restart re-resolves and re-sends.
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if (toMode == AlarmProviderMode.Subtag)
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{
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await RefreshSubtagCoverageAsync(cancellationToken).ConfigureAwait(false);
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}
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AlarmProviderStatus status;
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int fromModeInt;
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lock (_sync)
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@@ -565,14 +606,141 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
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}
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}
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// GWC-37: re-resolves the subtag watch-list and re-grades the coverage verdict without
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// touching the worker's subscription. Best-effort: a resolver that throws (only cancellation
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// and programming errors do — discovery failure is reported in the resolution) leaves the
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// verdict from the last subscribe in place, because a stale verdict is better than none.
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// Does not broadcast: the callers publish a status frame of their own immediately after.
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private async Task RefreshSubtagCoverageAsync(CancellationToken cancellationToken)
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{
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AlarmProviderMode forcedMode = MapForcedMode(_options.Fallback.Mode);
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AlarmWatchListResolution resolution;
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try
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{
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resolution = await _watchListResolver.ResolveAsync(_options, cancellationToken).ConfigureAwait(false);
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}
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catch (OperationCanceledException)
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{
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throw;
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}
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catch (Exception exception)
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{
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_logger.LogWarning(
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exception,
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"Re-resolving the alarm subtag watch-list failed; keeping the coverage verdict from the last subscribe.");
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return;
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}
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lock (_sync)
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{
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bool stale = !resolution.Targets
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.Select(target => target.AlarmFullReference)
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.ToHashSet(StringComparer.OrdinalIgnoreCase)
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.SetEquals(_sentWatchListReferences);
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SetSubtagCoverage(GradeSubtagCoverage(forcedMode, resolution, stale), broadcast: false);
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}
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}
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// Grades one resolution against the effective mode. Returns the reason the subtag coverage is
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// unsound, or an empty string when it is sound (or irrelevant, as under ForceAlarmManager).
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// Empty targets are the total-loss case; a failed discovery with a usable config-only list is
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// a completeness warning; drift is reported separately because the worker cannot be updated.
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private string GradeSubtagCoverage(
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AlarmProviderMode forcedMode,
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AlarmWatchListResolution resolution,
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bool staleAgainstSent)
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{
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// ForceAlarmManager never builds a subtag consumer, so its watch-list is genuinely unused.
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if (forcedMode == AlarmProviderMode.Alarmmgr)
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{
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return string.Empty;
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}
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// Nothing was asked of discovery and nothing was configured: subtag fallback is simply not
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// in use in this deployment (Auto with an empty list subscribes alarmmgr-only), so there is
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// no coverage to warn about.
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if (resolution.Targets.Count == 0
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&& !resolution.DiscoveryAttempted
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&& _options.Fallback.Discovery.IncludeAttributes.Length == 0
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&& forcedMode != AlarmProviderMode.Subtag)
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{
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return string.Empty;
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}
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List<string> reasons = [];
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if (resolution.Targets.Count == 0)
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{
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reasons.Add(AlarmProviderReasons.SubtagWatchListEmpty);
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}
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if (resolution.DiscoveryFailed)
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{
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reasons.Add(resolution.DiscoveryFailureMessage is { Length: > 0 } message
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? $"{AlarmProviderReasons.SubtagDiscoveryFailed} ({message})"
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: AlarmProviderReasons.SubtagDiscoveryFailed);
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}
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if (staleAgainstSent)
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{
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reasons.Add(
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$"{AlarmProviderReasons.SubtagWatchListStale} ({resolution.Targets.Count} target(s) now "
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+ $"resolve against {_sentWatchListReferences.Count} sent at subscribe); restart the alarm "
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+ "monitor to re-send it");
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}
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return string.Join("; ", reasons);
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}
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// Caller holds _sync. Applies a coverage verdict, logging and (optionally) broadcasting only
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// when it actually changed so a stable degraded state does not repeat a frame every pass.
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private void SetSubtagCoverage(string reason, bool broadcast)
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{
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bool missing = reason.Length > 0;
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if (missing == _subtagCoverageMissing && string.Equals(reason, _subtagCoverageReason, StringComparison.Ordinal))
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{
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return;
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}
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_subtagCoverageMissing = missing;
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_subtagCoverageReason = reason;
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if (missing)
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{
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_logger.LogWarning("Alarm subtag coverage is unsound: {Reason}", reason);
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}
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else
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{
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_logger.LogInformation("Alarm subtag coverage is sound.");
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}
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if (broadcast)
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{
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BroadcastToAll(new AlarmFeedMessage { ProviderStatus = BuildProviderStatus() });
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}
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}
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// Caller holds _sync. Builds an AlarmProviderStatus snapshot of the current state.
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//
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// GWC-37: degraded is the OR of "the subtag provider is the one serving" and "the subtag
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// watch-list cannot cover anything". The second is what makes an empty watch-list visible in
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// Auto mode, where the alarm manager is serving happily and the standby behind it is empty.
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// The reasons are concatenated when both apply, which is the worst case worth naming loudly:
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// failed over to a provider that covers nothing.
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private AlarmProviderStatus BuildProviderStatus()
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{
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bool degraded = _providerDegraded || _subtagCoverageMissing;
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string reason = (_providerReason, _subtagCoverageReason) switch
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{
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("", var coverage) => coverage,
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(var mode, "") => mode,
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(var mode, var coverage) => $"{mode} — {coverage}",
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};
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return new AlarmProviderStatus
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{
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Mode = _providerMode,
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Degraded = _providerDegraded,
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Reason = _providerReason,
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Degraded = degraded,
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Reason = reason,
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Since = Timestamp.FromDateTimeOffset(_providerSince),
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};
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}
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