feat(host): ClusterActivityEvaluator — oldest-member (singleton-host) active-node definition

2026-07-08 15:43:13 -04:00
parent 6b5c70dd19
commit 6320be9954
2 changed files with 96 additions and 0 deletions
@@ -0,0 +1,42 @@
+using Akka.Cluster;
+
+namespace ZB.MOM.WW.ScadaBridge.Host.Health;
+
+/// <summary>
+/// THE single definition of "active node" (review 01 [High]): a node is active
+/// when it is the OLDEST Up member (optionally within a role scope) — i.e. the
+/// member the ClusterSingletonManager places singletons on. Cluster LEADERSHIP
+/// (lowest address) is an Akka-internal concept that diverges from singleton
+/// placement permanently once the original first node restarts and rejoins;
+/// every product-level active/standby decision must use this evaluator, never
+/// cluster.State.Leader.
+/// </summary>
+public static class ClusterActivityEvaluator
+{
+    /// <summary>True when self is Up and no other Up member (in the role scope) is older.</summary>
+    public static bool SelfIsOldest(Cluster cluster, string? role = null)
+    {
+        var self = cluster.SelfMember;
+        if (self.Status != MemberStatus.Up)
+            return false;
+        if (role != null && !self.HasRole(role))
+            return false;
+
+        return cluster.State.Members
+            .Where(m => m.Status == MemberStatus.Up)
+            .Where(m => role == null || m.HasRole(role))
+            .All(m => m.UniqueAddress.Equals(self.UniqueAddress) || self.IsOlderThan(m));
+    }
+
+    /// <summary>The oldest Up member in the role scope, or null while none is Up. Used for Primary/Standby labelling.</summary>
+    public static Member? OldestUpMember(Cluster cluster, string? role = null)
+    {
+        Member? oldest = null;
+        foreach (var m in cluster.State.Members.Where(m => m.Status == MemberStatus.Up))
+        {
+            if (role != null && !m.HasRole(role)) continue;
+            if (oldest == null || m.IsOlderThan(oldest)) oldest = m;
+        }
+        return oldest;
+    }
+}