Per-cluster mesh Phase 6 merged to OtOpcUa master 2839deb5 (pushed 2026-07-24).
Records the split into one 2-node mesh per application Cluster, the consumer-visible
per-Cluster ServiceLevel/Primary scoping (two+ Primaries fleet-wide by design, no
wire-contract change), the SplitTopologyTransportValidator, pair-local secrets, and
the deferred live gate.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Phase 4 merged + pushed (tip 3a590a0c): driver-only nodes run with no ConfigDb
connection string. Consumer-visible ServiceLevel change — a DB-less site node
now holds 240/250 with central SQL down (survive-alone), where a DB-backed node
would drop to 0/100. Phases 0a/0b/1/2/3/4 done; 5-7 not started.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Update the OtOpcUa entry: the per-cluster mesh election-scoping fix now has Phases
0a/0b/1/2/3 merged + pushed (tip d01b0695). Phase 2 = ClusterClient command transport
(MeshTransport:Mode dark switch). Phase 3 = config fetch-and-cache — a FetchAndCache
driver node boots + serves last-known-good with central SQL down (extends the #485
availability guarantee consumers like ScadaBridge rely on); a failed fetch is 'no answer',
never an empty config. Live gate caught + fixed a Status==Sealed serve-gate deadlock.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Options investigation (Aspire standalone/HealthChecks.UI/Gatus/Homepage/
Grafana vs custom) → decision: custom ZB.MOM.WW.Overview Blazor app in the
family look. Design: anonymous read-only single pane, appsettings registry
of all four apps' instances, cache-first poller on a configurable timer,
configurable staleness timeout, Active/Standby from /health/active, and
per-cluster Akka leader chips (needs Health 0.2.0 optional per-entry data).
Impl plan: phased + code-verified — Phase 0 Health 0.2.0 (writer data field
+ AkkaClusterHealthCheck cluster view), Phase 1 ScadaBridge site-node
MapZbHealth PR (:8084; role-scoped active check), Phase 2 OtOpcUa bump,
Phase 3 the app (:5320), Phase 4 live rig acceptance. Mockup is the visual
reference: real Theme tokens + embedded IBM Plex, all card states incl.
stale + split-brain. Ready to execute in a fresh session.
Corrects the same-day report: PR searches for 'quic' missed work named
'artery'. Artery is landing rapidly on upstream dev as Artery-TCP (openspec
#8313; framing/handshake G1-G2; parallel lanes #8356/#8357; large-message
streamId 3 #8352; MNTR/CI for both transports), with Serialization.V2 in
parallel. TCP-first resolves §7's forward note: pipeline benefits arrive
without libmsquic, dropping the §6 platform constraints from the 1.6
adoption path. No previews or public benchmarks yet.
Two research reports (2026-07-22):
- akka_msquic_transport.md: what a QUIC transport on Akka 1.5.62 would take,
the 1.5-vs-1.6 pipeline delta that gates the benefits, .NET-native
alternatives (managed sockets ranked first), and measured throughput
evidence (PR #4594: transport swap is throughput-neutral).
- akka_multidc_clusters.md: JVM multi-DC semantics mapped onto the
central-pair + site-pairs topology, the stalled Akka.NET port (#3261 /
PR #4111), per-system fit vs the OtOpcUa mesh program, and the
before-Phase-2 decision point.
Recommendation in both: don't build; track upstream.
Both are consumer-visible, so they belong in the index rather than only in the
repo. The downing strategy moved to AutoDowning because a two-node OtOpcUa pair
on keep-oldest could not survive a crash of the oldest node — the same defect and
the same fix as ScadaBridge cf3bd52f, which is where the analysis came from. And
the redundancy Primary is now the oldest Up driver member rather than the role
leader, which changes which node advertises ServiceLevel 250 after a restart —
relevant to anything selecting a server by ServiceLevel.
Also notes that the four NU1903 advisories which broke ScadaBridge's fresh
restores were breaking OtOpcUa's too, and that the election remains scoped per
Akka cluster until the per-cluster mesh work lands.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
The #485/#486 fixes changed nothing structural about OtOpcUa — same drivers,
same dual-namespace scheme, same Galaxy flow — so the row is mostly untouched.
What DID change is a fact any OPC UA consumer depends on, and ScadaBridge is
mid-cutover onto exactly this address space: a transient ConfigDb error used to
empty the served address space (a PureRemove of every node, observed live and it
stayed empty), stop every driver and clear every subscription, while still
reporting the deploy Applied. A consumer would have seen all bindings go bad
with nothing upstream admitting a problem. Recorded on the OtOpcUa row.
Also fixes real drift found while checking: the OtOpcUa LocalDb adoption design
was sitting UNTRACKED here and unreferenced by the index, even though the
LocalDb row claims the adoption designs live in this repo. Now committed,
referenced alongside the ScadaBridge one, and its stale header corrected —
it still said Phase 1 was "not yet executed" against lib 0.1.1, when Phase 1
shipped and merged against 0.1.3. Phase 2 designed but not executed, on both
the doc and the row.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Two defects about a node whose LocalDb file is lost, the second only reachable
once the first was fixed:
- 0.1.2 — a converged pair prunes its oplog to empty on ack, and snapshot
detection read an empty oplog as 'no gap possible'. The steady state of a
healthy pair was the one state from which a rebuilt node could never be
back-filled.
- 0.1.3 — with back-fill working, the rebuilt node's OWN writes were silently
dropped: last_applied_remote_seq is a watermark in the peer's seq space and a
rebuilt peer numbers from 1, so the healthy node's stale watermark made the
sending side skip its whole oplog.
Both found by the OtOpcUa LocalDb Phase 1 live gate on the docker-dev rig and
reproduced offline as RED tests first. 149/149 pass.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
The other half of the rebuilt-peer story, and only reachable once 0.1.2 made
back-fill work: with the wiped node repopulated and writing again, its writes
never reached its peer.
last_applied_remote_seq is a watermark in the PEER's seq space, and a rebuilt
peer is a new database whose oplog numbers from 1. Two things then went wrong,
and both had to be fixed — the first alone leaves data stuck:
- The healthy node kept advertising the OLD peer's watermark, and the sending
side seeds its pump from exactly that number, so the rebuilt node skipped its
entire oplog. The watermark (and the observed peer clock) is now reset when
the peer's node id changes. last_acked_seq is deliberately NOT reset: it
describes our own oplog's pruned horizon and is what tells a rebuilt peer it
needs a snapshot — clearing it would turn 0.1.2's back-fill back off.
- A peer claiming to have applied more of our stream than we have ever produced
can only be remembering a previous incarnation of us. That claim is now
rejected in favour of starting from the beginning; LWW makes the re-send
harmless. This mirrors the clamp RecordPeerAckAsync already applies to acks.
Found on the OtOpcUa docker-dev rig, where the healthy node held watermark 10
while the rebuilt peer's oplog was seqs 1-3 and its last_acked stayed 0 — the
peer never accepted a single one. Covered by a test that converges with one
peer, replaces it with a fresh database, and requires a write on the new peer
to arrive: RED before this fix, green after. 149/149 pass.
Version 0.1.3.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
The lib row still claimed ScadaBridge was the only consumer (verified
2026-07-20); OtOpcUa's Phase 1 adoption merged 2026-07-21. Records 0.1.2 and
the wiped-peer snapshot fix it carries.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
A converged pair prunes its oplog on ack, so "no oplog rows at all" is the
steady state of a healthy pair — not an anomaly. ComputeSnapshotRequiredAsync
measured the peer's gap against the oldest surviving oplog row and treated an
empty oplog as "no gap possible", which made that steady state the one state
from which a wiped peer could never be healed: it reconnected with an empty
database and a zero watermark, was told it needed no snapshot, and stayed
empty indefinitely.
With an empty oplog the oldest seq we could still stream is one past
last_acked_seq — ack-pruning is the only thing that empties the oplog without
also flagging needs_snapshot, and it deletes exactly seq <= last_acked_seq.
Measuring the gap against that heals the wiped peer and leaves every other
case identical: a converged peer's watermark equals last_acked_seq (no
snapshot), and a pair that has never written anything has both at zero.
Found by the OtOpcUa LocalDb Phase 1 live gate (check 4), which recorded it as
a documented limitation. Covered by a test that reproduces the live-gate
scenario through the real session stack: RED before this fix (the wiped side
never converges, 15 s timeout), green after. 148/148 pass.
Version 0.1.2.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Phases 1 and 2 landed on ScadaBridge main together as PR #23
(merge 28ca04d7) on 2026-07-20 and were pushed to origin. The
component row still described both as unmerged branches.
Verified before editing: main..feat/localdb-phase1 and
main..feat/localdb-phase2 are both empty, main == origin/main,
and SiteReplicationActor/ReplicationService have no hits left in
main's tree.
Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts
The row still said "Adopted by ScadaBridge (Phase 1 only)" and "Phase 2 is NOT
started". Both phases are now complete with a 10-check live gate PASS.
Also records what the row could not have said before: the 0.1.1 parent-
directory boot fix, that ScadaBridge is the library's ONLY consumer (verified —
OtOpcUa, mxgw and HistorianGateway have no LocalDb reference at all), the
deliberate never-registered status of notification_lists/smtp_configurations
and why, and the three operational constraints an operator has to know
(stop/start a pair together, the TombstoneRetention resurrection bound, and
MaxBatchSize batching by row count against a 4 MB gRPC cap).
Replication remains default-OFF and no production deployment has it enabled.
Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts
Closes criterion 5 of ScadaBridge/docs/known-issues/2026-07-20-localdb-disk-io-
error-under-load.md §9: Phase 1 shipped only correctness and convergence tests,
so nothing exercised many pooled per-operation connections writing a REGISTERED
table (capture trigger + zb_hlc_next UDF) concurrently — which is exactly the
shape the ScadaBridge site nodes run under load.
8 writers x 250 inserts, one fresh pooled connection per operation, with
concurrent readers churning the pool and the WAL index throughout. Asserts both
that every write lands and that the oplog captured each exactly once, so a
trigger that dropped or double-counted under contention fails it.
Written during the 2026-07-20 disk-I/O incident investigation and left
uncommitted; the incident itself was root-caused to host-side sqlite3 access on
a bind-mounted WAL database, not a library defect.
Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts
SQLite creates the database FILE on demand but never its parent DIRECTORY, and
SqliteLocalDb opens the file eagerly in its constructor — so a configured path
under a not-yet-existing directory was a hard startup failure ("SQLite Error
14: unable to open database file") rather than a first run that just worked.
Relative defaults like ./data/app.db hit it routinely; a containerized consumer
escapes only when a volume mount happens to create the directory first.
ScadaBridge found this during LocalDb Phase 2 and worked around it app-side
(SiteLocalDbDirectory.Ensure). Every other consumer still had the gap, so the
guarantee belongs here.
The standing objection to a library that creates directories is that it can
mask a mis-typed path by silently starting an empty database. That does not
apply: SQLite ALREADY does exactly that for a mis-typed file NAME. Refusing to
create the directory protects nothing — it only makes the two halves of one
path behave inconsistently and turns the directory half into an opaque error.
A creation failure (permissions, read-only mount) now throws an
InvalidOperationException naming the directory and the cause, instead of
surfacing as SQLite error 14. That is a change of exception type, but only on a
path that already failed hard.
Both behaviours are pinned and verified to fail with the call removed.
147 tests pass, 0 warnings. Published to the Gitea feed at 0.1.1.
Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts
Environment.SetEnvironmentVariable/GetEnvironmentVariable mutate the
process-wide environ; concurrent setenv/getenv across parallel xunit test
classes is a documented crash/flake source on glibc even with unique
variable names. Group the six classes that touch process env vars into a
DisableParallelization=true collection so they run serially against each
other while everything else keeps running in parallel.
Was 'no app adoption yet'. Now records the honest state: ScadaBridge site nodes
adopted Phase 1 on an UNMERGED branch, replication wired but default-OFF and
live-proven on the docker rig's site-a pair only, Phase 2 not started, no other
app adopted, no production deployment replicating.
Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts
Joseph Doherty