Promotes the two apps' private replacements for ActiveNodeHealthCheck into one
shared primitive, and retires the leader/RoleLeader selection they were written
to avoid.
Both Akka consumers had already hand-rolled a replacement rather than use this
package (ScadaBridge OldestNodeActiveHealthCheck, OtOpcUa
ClusterPrimaryHealthCheck), so the entire active-node surface here —
ActiveNodeHealthCheck, AkkaActiveNodeGate — had ZERO consumers. It was not
merely unused: it was avoided, twice, for the same reason.
Leadership is address-ordered (host, then port) and has no relationship to time;
singleton placement is age-ordered. The two agree on a freshly-formed cluster,
which is why single-node and happy-path tests never caught it. They diverge
permanently after any restart: the restarted node rejoins as the youngest but
keeps its address, so if it holds the lower address it becomes leader while the
singletons — and all the work they own — stay on the other node.
New ClusterActiveNode is the single implementation: oldest Up member, optional
role scope, plus role-preference resolution for a fused node that must answer
for the role its singletons are pinned to. ActiveNodeHealthCheck and
AkkaActiveNodeGate both delegate to it, so an endpoint gate and the
/health/active probe an orchestrator routes by cannot disagree.
BREAKING (behaviour, not signature):
- Selection is by age, not leadership.
- The role-filtered mode no longer reports Healthy for a node LACKING the role.
That "not applicable => Healthy" made the tier answer 200 on every node and
silently broke leader-pinning (lmxopcua#494); it is now Unhealthy by default,
overridable via NoActiveRoleStatus. This case is reachable, not defensive —
OtOpcUa's RoleParser admits dev-only and cluster-role-only nodes.
- Identity compares UniqueAddress, so a node restarted on the same host:port is
correctly a different member during the overlap.
Results now carry activeRole/selfAddress/activeNode in the 0.2.0 per-entry data
object, so a standby reports WHO is active and a dashboard can render a pair
from either node's payload alone.
Tests: 45 Akka (was 39), 76 total. The age-vs-address divergence is pinned
against a real two-node cluster built so the oldest member is not the
lowest-addressed one, with a fixture sanity check so it cannot pass for the
wrong reason.
Joseph Doherty
a61e041e58