A caller addressing a standby central node directly (or hitting Traefik inside its
/health/active probe window after a failover) used to get 503 STANDBY_NODE. The
standby now relays the request verbatim to the active peer over HTTP
(IStandbyRequestForwarder / HttpStandbyRequestForwarder) and replays the response;
method scripts and Route.To() still execute only on the active node.
- ScadaBridge:InboundApi:StandbyForwardPeerEndpoints (static list of the OTHER
central node's HTTP base URL; empty = old 503 behaviour) + StandbyForwardTimeout
(60s), both startup-validated.
- Peers tried in order: peer 503 stamped X-ScadaBridge-Standby, connection failure
or timeout → next peer; all fail → 503 ACTIVE_NODE_UNREACHABLE. A 503 without
the marker is the active node's own answer and is replayed.
- One-hop loop guard via X-ScadaBridge-Forwarded; 413 body cap now runs BEFORE
the active-node check so a standby never buffers/relays an oversized body.
- AuditWriteMiddleware skips its own ApiInbound row for a relayed request so a
call is audited once, on the node that executed it.
- Rig + env2 central nodes configured; spec (Component-InboundAPI.md → Standby
forwarding), Component-Host.md options row, CLAUDE.md updated.
- 20 new tests (filter decision + relay mechanics + validator).
Claude-Session: https://claude.ai/code/session_019ZxXT5sxZs5XrtdwYzJDPV
WP2.6 (arch-review remediation, cross-cutting misc):
- SiteExternalSystemRepository: name/ID-indexed ExternalSystemDefinitionCache replaces
the fetch-all + reverse-map scan on every by-ID/method lookup; loaded once per
redeploy, invalidated by DeploymentManagerActor after HandleDeployArtifacts applies
external-system changes. Static JsonSerializerOptions for method-list parsing.
- Inbound API: short-TTL ApiMethodCache fronts the per-request ApiMethod repository
fetch; invalidated by name via the existing ScriptArtifactChangeSubscriber/
IScriptArtifactChangeBus pipeline, self-healing via TTL for changes the bus
doesn't cover (e.g. Management API edits).
- StoreAndForward: the cached-call audit-observer queue — the one unbounded channel
left in the system — is now bounded (ObserverQueueCapacity, default 10,000) with
DropOldest overflow and a dropped-notification counter.
- SiteStreamManager: alarm state changes now travel a dedicated publish
source/broadcast hub, isolated from the (far higher-volume) attribute path, so an
attribute storm can no longer evict a pending alarm transition; the alarm hand-off
queue is bounded with a drop counter surfaced on the site health report
(SiteStreamAlarmDropCount via the new SiteStreamAlarmDropReporter), and publishing
is skipped entirely at zero subscribers on either path.
- CLI ManagementHttpClient: explicit 30s HttpClient.Timeout on the shared
construction (was the 100s framework default), overridable via
SCADABRIDGE_HTTP_TIMEOUT_SECONDS.
Deviation: the failback-probe heartbeat item is NOT included — its only viable
surface (CentralChannelProvider.cs / heartbeat consumers) lives entirely in the
Communication project, explicitly off-limits to this work package this phase.
Tests: SiteRuntime.Tests (550), InboundAPI.Tests (278), StoreAndForward.Tests (133),
CLI.Tests (390), HealthMonitoring.Tests (97) — all green after full solution build.
Joseph Doherty