Akka runs FirstSeedNodeProcess -- the only bootstrap path that can form a NEW
cluster when no peer answers InitJoin -- exclusively when seed-nodes[0] is the
node's own address. Every other node runs JoinSeedNodeProcess and retries
InitJoin forever. That is why "both peers are seeds" never meant "either can
cold-start alone", and it is fixed here the way Akka itself intends: each seed
node lists ITSELF first.
- docker-dev central-2 now lists itself as SeedNodes__0 (central-1 was already
self-first). The site nodes are untouched -- they seed off central-1 only and
are deliberately not seeds.
- AkkaClusterOptionsValidator enforces the invariant at boot via the shared
ZB.MOM.WW.Configuration AddValidatedOptions/ValidateOnStart seam. The rule is
CONDITIONAL -- self must be seed[0] only IF self is in the list at all -- or it
would refuse to boot every driver-only site node. Identity is compared on
PublicHostname (falling back to Hostname when blank) AND port, i.e. the address
Akka puts in SelfAddress: matching the 0.0.0.0 bind address would find no seed
anywhere and leave the rule silently inert on the whole docker-dev rig.
- ClusterBootstrapFallback + Cluster:SelfFormAfter are DELETED. The watchdog sat
outside Akka's join handshake, so it could not distinguish "no seed answered"
from "a seed answered and the join is in flight" -- and Cluster.Join(SelfAddress)
is not ignored mid-handshake, it wins. The live gate (ea45ace1) caught it
islanding a node that a manual failover had bounced: InitJoinAck received, no
Welcome inside the window because the peer's ring still held the old
incarnation, watchdog fired, second cluster. The TCP reachability guard patched
that one shape; the race stayed. It was also inert for every non-seed node, so
after this change it can never usefully fire.
- SelfFormBootstrapTests -> SelfFirstSeedBootstrapTests: real in-process clusters
through the production bootstrap at production failure-detection timings, incl.
a falsifiability control proving the OLD peer-first ordering never forms (that
test failed at 11s against the watchdog, which is what proved the retirement),
the restart-into-a-live-peer case that killed the watchdog, and a simultaneous
cold start converging on ONE cluster.
Mirrors ScadaBridge 4a6341d8; anticipates per-cluster-mesh-program Phase 6, which
had this retirement queued.
Ports the sister project's live-proven fix (ScadaBridge cf3bd52f). OtOpcUa ran
the identical configuration it indicts: keep-oldest with down-if-alone = on.
Akka.NET 1.5.62's KeepOldest.OldestDecision only lets the down-if-alone branch
rescue a side holding >= 2 members. A two-node cluster losing a peer is always a
1-vs-1 split, so the branch never fires, the lone survivor falls through to
DownReachable and downs ITSELF, and run-coordinated-shutdown-when-down then
terminates it. down-if-alone is a 3+-node feature and does not do what its name
suggests for a pair: a crash of the oldest node is a total outage, which is the
exact failure the redundancy pair exists to absorb.
Cluster:SplitBrainResolverStrategy now selects the provider, defaulting to
auto-down: Akka's AutoDowning with auto-down-unreachable-after = 15s, so the
leader among the reachable members downs the unreachable peer and a crash of
either node fails over in place. keep-oldest remains available for deployments
that would rather take an outage than ever run dual-active during a real
partition. An unrecognised value fails the host at startup rather than falling
through to the fatal default.
The tests assert the EFFECTIVE configuration — they start a real host through
WithOtOpcUaClusterBootstrap and read akka.cluster.downing-provider-class back off
the running ActorSystem. This is not incidental. The first draft inlined the
three calls the bootstrap makes instead of calling it, which pinned the test's
own wiring: sabotaging production's HOCON precedence left all 36 green. The
prior file had the same shape at a smaller scale, asserting only that
BuildClusterOptions returned a KeepOldestOption — true, and true of a
configuration that cannot fail over. Positive control: making BuildDowningHocon
emit nothing for auto-down turns exactly the two effective-config guards red.
Measured while verifying rather than assumed: HoconAddMode.Append also wins here,
purely because it is added last, so the mode name is not the guarantee. The
comment now says so instead of asserting a precedence rule that does not hold.
Not yet live-drilled on OtOpcUa. The docker-dev rig is a single six-node mesh
where the 1-vs-1 pathology cannot occur; the kill-the-oldest drill belongs with
the per-cluster mesh work that makes every mesh exactly two nodes (design doc
6.2 / Phase 0a). Recorded as an outstanding gate in docs/Redundancy.md.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Adds <summary>, <param>, <typeparam>, and <inheritdoc/> tags to public
members surfaced by commentchecker — resolves 5,847 of 5,869 issues
(99.6%) across three /fixdocs passes.
Joseph Doherty