Joseph Doherty
40 lines
2.0 KiB
C#
40 lines
2.0 KiB
C#
using Akka.Cluster;
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namespace ZB.MOM.WW.ScadaBridge.Communication.ClusterState;
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/// <summary>
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/// THE single definition of "active node" (review 01 [High]; review 02 round 2 [Critical] N1):
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/// a node is active when it is the OLDEST Up member (optionally within a role scope) — i.e.
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/// the member the ClusterSingletonManager places singletons on. Cluster LEADERSHIP (lowest
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/// address) is an Akka-internal concept that diverges from singleton placement permanently
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/// once the original first node restarts and rejoins; every product-level active/standby
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/// decision must use this evaluator, never <c>cluster.State.Leader</c>.
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/// <para>
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/// Lives in Communication (not Host) so BOTH <c>SiteCommunicationActor</c> and
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/// <c>SiteReplicationActor</c> can default to it — Host cannot be referenced from either.
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/// The Host's <c>ClusterActivityEvaluator.SelfIsOldest</c> delegates here, so the S&F
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/// delivery gate (<c>IClusterNodeProvider.SelfIsPrimary</c>), the resync authority checks,
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/// and the heartbeat IsActive stamp all share one implementation.
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/// </para>
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/// </summary>
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public static class ActiveNodeEvaluator
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{
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/// <summary>True when self is Up and no other Up member (in the role scope) is older.</summary>
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/// <param name="cluster">The Akka cluster to evaluate.</param>
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/// <param name="role">Optional role scope; when set, only members with this role are considered.</param>
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/// <returns><c>true</c> when self is Up and the oldest Up member in the role scope.</returns>
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public static bool SelfIsOldestUp(Cluster cluster, string? role = null)
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{
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var self = cluster.SelfMember;
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if (self.Status != MemberStatus.Up)
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return false;
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if (role != null && !self.HasRole(role))
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return false;
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return cluster.State.Members
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.Where(m => m.Status == MemberStatus.Up)
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.Where(m => role == null || m.HasRole(role))
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.All(m => m.UniqueAddress.Equals(self.UniqueAddress) || self.IsOlderThan(m));
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}
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}
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