ClusterPrimaryHealthCheck was written three days' worth of debugging ago because
the shared ActiveNodeHealthCheck selected by RoleLeader and reported Healthy for
any node lacking the role. Health 0.3.0 fixes the shared check — oldest Up
member, role-preference scoping, Unhealthy when the node owns no active work —
so the private copy is now duplication rather than a workaround, and it is
deleted.
RolePreference [admin, driver] reproduces exactly what it did: a fused central
node answers for admin (where the singletons and the AdminUI are pinned), a
driver-only site node answers for driver.
SelectOldestUpMemberOfRole now delegates to the shared ClusterActiveNode instead
of re-implementing the age ordering. This is the point of the change rather than
a tidy-up: the redundancy snapshot drives the OPC UA ServiceLevel 250/240 split
while the health tier drives Traefik's admin routing, so two copies of "oldest Up
member of a role" would be two chances to advertise one node as authoritative
while gating the data plane on another. ControlPlane takes a ZB.MOM.WW.Health.Akka
reference for it; the layering trade-off is recorded at the PackageReference.
Behaviour note: a node carrying neither admin nor driver now answers 503 on the
active tier instead of 200. That case is reachable — RoleParser admits dev-only
and cluster-role-only nodes — and 503 is correct, since such a node owns no
active work and must not be in an active-tier pool. No docker-dev node is
affected: every rig node is admin+driver or driver-only.
Tests replaced in kind. The rule itself is now pinned in the library against a
real two-node cluster; what stays OtOpcUa's own decision is the wiring, so
ActiveTierRegistrationTests pins which check is on the active tag, that it is
registered on driver-only nodes too, and that it is not on the ready tier.
Verified: Host.Tests 25/25, ControlPlane redundancy 15/15.
Closes the remaining half of #494, and corrects the half fixed in 8dd9da7d.
The shared ActiveNodeHealthCheck(role: "admin") answered the wrong question twice
over. It returns Healthy for any node LACKING the role, so all four driver-only
site nodes called themselves active and no consumer could find the Primary of a
site Cluster. And it selects by RoleLeader - the lowest-ADDRESSED member - which
is not where Akka places singletons.
Replaced with ClusterPrimaryHealthCheck ("cluster-primary"). One rule: this node
is active iff it is the OLDEST Up member carrying its own active role, where the
active role is admin when the node has it and driver otherwise. That serves both
consumers correctly - a fused admin node answers for admin, so Traefik pins the
AdminUI to the node hosting the singletons; a driver-only site node answers for
driver, which is exactly SelectDriverPrimary, the same election behind
IsDriverPrimary and the OPC UA ServiceLevel 250/240 split. Per-mesh scoping is
free after Phase 6: ClusterState.Members already contains only this node's own
Cluster.
SelectDriverPrimary is generalised to SelectOldestUpMemberOfRole so the
age-ordering rule has one implementation. Two copies of "oldest Up member of a
role" would be two chances to silently disagree about who is in charge, and the
tier and the redundancy snapshot must never disagree.
THE ROLE-LEADER HALF MATTERED IN PRACTICE, not just in theory. On the rebuilt rig
the two orderings diverge right now:
akka leader (lowest address) = central-1
oldest admin member = central-2 <- hosts the singletons
8dd9da7d made the tier a real 503 but still selected by RoleLeader, so it would
have pinned Traefik to central-1 - the node NOT hosting the work. With this change
Traefik correctly routes to central-2.
Live-verified, exactly one 200 per mesh:
MAIN central-2 200 central-1 503 traefik: central-2 UP, central-1 DOWN
SITE-A site-a-1 200 site-a-2 503
SITE-B site-b-1 200 site-b-2 503
Tests: role-selection matrix and the startup-safe Degraded path in Host.Tests
(26 pass); parity between the tier's selector and the redundancy snapshot's, plus
role scoping, added to RedundancyPrimaryElectionTests, which forms a real two-node
cluster deliberately built so the oldest member is not the lowest-addressed one
(5 pass).
Joseph Doherty