OldestNodeActiveHealthCheck existed because the shared ActiveNodeHealthCheck
selected by cluster leadership (review 01 [High]): leadership is address-ordered
and diverges from singleton placement after a restart, and during a partition
both sides compute themselves leader so Traefik served both. Health 0.3.0 makes
the shared check age-based — it is now this host's own rule, promoted — so the
private copy is deleted and central registers the shared type.
ActiveNodeEvaluator, the "THE single definition of active node" this repo already
maintained, now delegates to the shared ClusterActiveNode rather than
re-implementing it. That keeps the delivery gate, the heartbeat IsActive stamp,
the inbound-API gate and the /health/active tier on one rule, and it means the
rule is shared with OtOpcUa, which had independently written a third copy.
Communication takes a ZB.MOM.WW.Health.Akka reference for it; the layering
trade-off is recorded at the PackageReference.
SitePairActiveNodeHealthCheck is deliberately KEPT. It is not a duplicate of the
rule — it is a thin adapter over the site's own IClusterNodeProvider, which
scopes to site-{SiteId} and is itself now backed by ClusterActiveNode. Registering
the shared check directly would have to re-derive the site role and would lose the
property that the tier and singleton placement come from the same provider.
Central stays unscoped: every central member competes for one active slot.
No behaviour change on any node — same rule, one implementation instead of two.
Verified: Host.Tests 439/439, Communication ActiveNode 2/2.
Site nodes served no health surface at all — gRPC on the HTTP/2-only listener and
/metrics on the HTTP/1.1 one — so nothing outside the cluster could ask a site
node whether it was ready or which half of the pair was active. The family
overview dashboard probes every instance the same way, and this is the one gap.
Three checks, registered in SiteServiceRegistration.Configure (not Program.cs, so
the composition-root tests that build this graph actually cover them) and mapped
by app.MapZbHealth() on the site's HTTP/1.1 listener (default :8084) alongside
/metrics:
akka-cluster [Ready] the shared AkkaClusterHealthCheck. Also carries the
cluster-view data (leader/memberCount/...) the dashboard
reads, free with ZB.MOM.WW.Health 0.2.0.
localdb [Ready] NEW SiteLocalDbHealthCheck — SELECT 1 through the
registered ILocalDb. Site has no EF context; central's
DatabaseHealthCheck<ScadaBridgeDbContext> is central-only.
Replication state rides along as data ENRICHMENT only:
replication is default-OFF, so failing on it would mark
every correctly-configured node unready.
active-node [Active] NEW SitePairActiveNodeHealthCheck, delegating to
IClusterNodeProvider.SelfIsPrimary. Deliberately NOT
central's OldestNodeActiveHealthCheck: that one calls
SelfIsOldest(cluster) with no role argument and would
compute "oldest" across the wrong member set on a mesh
carrying more than one site.
Anonymous, as central's are: the site pipeline runs no authentication middleware
and has no FallbackPolicy, so nothing extra was needed.
Also bumps ZB.MOM.WW.Health* 0.1.0 -> 0.2.0 (central gains data.leader for free).
Tests: SiteHealthCheckTests builds the REAL site container and activates every
registration through its factory (exact-set names, one tier tag each, resolved
types, central-only checks absent behind a positive control) plus behaviour for
both new checks. SiteHealthEndpointTests boots the real site Program over
WebApplicationFactory and proves the endpoints are MAPPED — without it, deleting
MapZbHealth would leave every registration test green while site nodes 404'd.
Prereq for scadaproj docs/plans/2026-07-22-overview-dashboard-impl-plan.md Phase 1.
Joseph Doherty