Corrects the #459 finding. 2-node keep-oldest recovery works fine (the ScadaBridge
sister project proves it); OtOpcUa was missing the supervision pieces that make it
automatic, and docs/Redundancy.md wrongly claimed in-place oldest-crash failover.
Mechanism (confirmed on a 2-container rig + by decompiling Akka KeepOldest.OldestDecision):
on an OLDEST-node crash keep-oldest downs the LONE survivor (DownReachable including
myself) — down-if-alone can't rescue a lone survivor (its branch needs >=2 survivors).
Recovery is exit-and-rejoin: run-coordinated-shutdown-when-down terminates the node and
the service supervisor restarts it. My earlier 'total outage' was a docker-dev artifact
(no restart policy); production Install-Services.ps1 already has sc.exe failure restart.
Changes (ScadaBridge parity):
- ActorSystemTerminationWatchdog (Host, registered after AddAkka): watches
ActorSystem.WhenTerminated and on an unexpected self-down calls StopApplication so the
process exits (supervisor restarts it) instead of idling with a dead actor system.
Distinguishes graceful shutdown via _stopRequested + ApplicationStopping. 3 unit tests.
- docker-dev: restart: unless-stopped on the host anchor (models production supervision) +
both redundancy peers in SeedNodes so a restarted node re-forms via either peer.
- docs/Redundancy.md: rewrote the split-brain recovery section — younger-loss = in-place
fast failover; oldest-loss = exit-and-rejoin under supervision (not in-place); the three
requirements (supervisor + watchdog + both-node seeds); flagged HardKillFailoverTests as
non-representative (Transport.Shutdown, not a real crash). Instant in-place takeover on
ANY single loss needs 3+ members.
Cluster.Tests 29/29 (SBR guards), watchdog tests 3/3, full solution builds.
Live re-verify of the watchdog image pending (host docker disk full).
Joseph Doherty
b0eb653bad