Joseph Doherty
f862804a35
Design for review, mirroring the ScadaBridge hub-and-spoke shape. Researched from
the ScadaBridge tree directly rather than from its CLAUDE.md, which understates
the boundary in five ways: there are THREE transports (ClusterClient, gRPC, plus
token-gated HTTP), the gRPC direction is inverted (central dials INTO each site),
active node is the OLDEST Up member and explicitly never the cluster leader, all
clusters share one ActorSystem name, and site nodes carry two roles.
Records a defect worth fixing regardless of the topology decision: OtOpcUa uses
two different node-selection rules at once. SBR is keep-oldest and singletons are
placed on the oldest member, but RedundancyStateActor elects Primary from
RoleLeader("driver") — lowest address. Those diverge permanently after a
restart-and-rejoin, so the node the SBR protects and hosts every singleton on need
not be the node the data-plane gates consider Primary. ScadaBridge forbids that
rule by name, for the reason it gives: both sides claim leadership during a
partition, which is the dual-primary shape archreview 03/S4 exists to prevent.
Three open questions are left explicitly undecided: whether to adopt their
autonomous-site data architecture or keep the shared ConfigDb; what to do about
the registered two-node keep-oldest total-outage gap they acknowledge but have not
closed; and whether to authenticate transports they left unauthenticated.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
OtOpcUa documentation
Two tiers of documentation live here:
- Current reference at the top level (
docs/*.md) — describes what's shipped today. Start here for operator + integrator reference. - Implementation history + design notes at
docs/v2/*.md— the authoritative plan + decision log the current reference is built from. Start here when you need the why behind an architectural choice, or when a top-level doc says "see plan.md § X".
The project was originally called LmxOpcUa (a single-driver Galaxy/MXAccess OPC UA server) and has since become OtOpcUa, a multi-driver OPC UA server platform. Any lingering LmxOpcUa-string in a path you see in docs is a deliberate residual (executable name lmxopcua-cli, client PKI folder {LocalAppData}/LmxOpcUaClient/) — fixing those requires migration shims + is tracked as follow-ups.
Platform overview
v2 (2026-05-26): the separate
OtOpcUa.Server+OtOpcUa.Adminservices fused into a single role-gatedOtOpcUa.Hostbinary, joined by an Akka.NET cluster. See v2 design for the architectural decision.
- Core owns shared abstractions (driver capability contracts, scripting, virtual tags, alarm historian).
- Drivers plug in via capability interfaces in
ZB.MOM.WW.OtOpcUa.Core.Abstractions:IDriver,IReadable,IWritable,ITagDiscovery,ISubscribable,IHostConnectivityProbe,IAlarmSource,IHistoryProvider,IPerCallHostResolver. Each driver opts into whichever it supports. - Host (
src/Server/ZB.MOM.WW.OtOpcUa.Host) is the single fused binary (.NET 10, AnyCPU).OTOPCUA_ROLESenv decides what to mount:admin(Blazor + control-plane singletons),driver(OPC UA endpoint + per-node actors), or both. See ServiceHosting.md. - Cluster + ControlPlane + Runtime + AdminUI + Security sit between Core and Host. The cluster glues per-node actors into one logical fleet; the control-plane singletons (deploy coordinator, audit writer, redundancy state) live on the admin role-leader. See Redundancy.md.
- The Galaxy driver still reaches MXAccess via gRPC to a separately-installed mxaccessgw sidecar (sibling repo).
Where to find what
Architecture + data-path reference
| Doc | Covers |
|---|---|
| OpcUaServer.md | Top-level server architecture — Core, driver dispatch, Config DB, generations |
| AddressSpace.md | GenericDriverNodeManager + ITagDiscovery + IAddressSpaceBuilder |
| ReadWriteOperations.md | OPC UA Read/Write → CapabilityInvoker → IReadable/IWritable |
| DriverLifecycle.md | Server-side driver lifecycle + infrastructure contracts (IDriverFactory, IDriverProbe, IDriverSupervisor, IDriverHealthPublisher, IDriverConfigEditor, IHistorianDataSource) + the Commons library |
| Subscriptions.md | Monitored items → ISubscribable + per-driver subscription refcount (v1 archive) |
| AlarmTracking.md | IAlarmSource + AlarmSurfaceInvoker + OPC UA alarm conditions — native Galaxy alarms end-to-end (live) |
| AlarmTracking.md | Original alarm-tracking write-up (v1 archive) |
| AlarmHistorian.md | Core.AlarmHistorian store-and-forward sink — LocalDbStoreAndForwardSink, the replicated alarm_sf_events buffer + Primary-only drain, IAlarmHistorianWriter, dead-letter/retry/eviction |
| DataTypeMapping.md | Per-driver DriverAttributeInfo → OPC UA variable types (v1 archive — live mapping is in src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Browse/DataTypeMap.cs) |
| IncrementalSync.md | Address-space rebuild on redeploy + sp_ComputeGenerationDiff |
| HistoricalDataAccess.md | IHistoryProvider as a per-driver optional capability (v1 archive) |
| VirtualTags.md | Core.Scripting + Core.VirtualTags — Roslyn script sandbox, engine, dispatch alongside driver tags |
| ScriptEditor.md | Monaco script editor — Roslyn-backed IntelliSense (completions, diagnostics, hover, tag-path) for C# virtual-tag scripts; AdminUI/ScriptAnalysis/ backend |
| ScriptedAlarms.md | Core.ScriptedAlarms — script-predicate IAlarmSource + Part 9 state machine |
One Core subsystem is shipped without a dedicated top-level doc; see the section in the linked doc:
| Project | See |
|---|---|
Analyzers (Roslyn OTOPCUA0001) |
security.md § OTOPCUA0001 Analyzer |
Drivers
| Doc | Covers |
|---|---|
| drivers/README.md | Index of the eight shipped drivers + capability matrix |
| drivers/Galaxy.md | Galaxy driver — in-process gRPC client to the mxaccessgw sidecar |
| v1/drivers/Galaxy-Repository.md | Galaxy-specific discovery via the ZB SQL database (v1 archive — the gateway owns this path now) |
For Modbus / S7 / AB CIP / AB Legacy / TwinCAT / FOCAS / OPC UA Client specifics, see v2/driver-specs.md.
Operational
| Doc | Covers |
|---|---|
| Configuration.md | Live appsettings + environment-variable reference (current state) |
| Configuration.md | appsettings bootstrap + Config DB + Admin UI draft/publish (v1 archive — OTOPCUA_GALAXY_* env vars now live in mxaccessgw config) |
| Uns.md | The global /uns master tree — manage Area/Line/Equipment/Tag/VirtualTag fleet-wide; replaces the per-cluster UNS/Equipment/Tags tabs |
| security.md | Transport security profiles, LDAP auth, ACL trie, role grants, OTOPCUA0001 analyzer |
| Redundancy.md | RedundancyCoordinator, ServiceLevelCalculator, apply-lease, Prometheus metrics |
| Reservations.md | Fleet-wide ZTag / SAPID external-ID reservations — publish-time claim, release flow |
| ServiceHosting.md | Single fused OtOpcUa.Host binary install/uninstall with OTOPCUA_ROLES gating; the historian backend is the external HistorianGateway |
| StatusDashboard.md | Pointer — superseded by v2/admin-ui.md |
Client tooling
| Doc | Covers |
|---|---|
| Client.CLI.md | otopcua-cli — OPC UA command-line client |
| Client.UI.md | Avalonia desktop client |
| DriverClis.md | Driver test-client CLIs — index + shared commands |
| Driver.Modbus.Cli.md | otopcua-modbus-cli — Modbus-TCP |
| Driver.AbCip.Cli.md | otopcua-abcip-cli — ControlLogix / CompactLogix / Micro800 / GuardLogix |
| Driver.AbLegacy.Cli.md | otopcua-ablegacy-cli — SLC / MicroLogix / PLC-5 (PCCC) |
| Driver.S7.Cli.md | otopcua-s7-cli — Siemens S7-300 / S7-400 / S7-1200 / S7-1500 |
| Driver.TwinCAT.Cli.md | otopcua-twincat-cli — Beckhoff TwinCAT 2/3 ADS |
| Driver.FOCAS.Cli.md | otopcua-focas-cli — Fanuc FOCAS/2 CNC |
Requirements
| Doc | Covers |
|---|---|
| reqs/HighLevelReqs.md | HLRs — numbered system-level requirements |
| reqs/OpcUaServerReqs.md | OPC UA server-layer reqs |
| v1/reqs/ServiceHostReqs.md | Per-process hosting reqs (v1 archive — only OtOpcUa server hosting remains in scope post-PR-7.2) |
| reqs/ClientRequirements.md | Client CLI + UI reqs |
| v1/reqs/GalaxyRepositoryReqs.md | Galaxy-scoped repository reqs (v1 archive — owned by mxaccessgw today) |
| v1/reqs/MxAccessClientReqs.md | Galaxy-scoped MXAccess reqs (v1 archive — owned by mxaccessgw today) |
| reqs/StatusDashboardReqs.md | Pointer — superseded by Admin UI |
Implementation history (docs/v2/)
Design decisions + phase plans + execution notes. Load-bearing cross-references from the top-level docs:
- v2/plan.md — authoritative v2 vision doc + numbered decision log (referenced as "decision #N" elsewhere)
- v2/admin-ui.md — Admin UI spec
- v2/acl-design.md — data-plane ACL + permission-trie design (Phase 6.2)
- v2/config-db-schema.md — Config DB schema reference
- v2/driver-specs.md — per-driver addressing + quirks for every shipped protocol
- v2/dev-environment.md — dev-box bootstrap
- v2/test-data-sources.md — integration-test simulator matrix (includes the pinned libplctag
ab_serverversion for AB CIP tests) - v2/multi-host-dispatch.md — per-PLC circuit breakers (Phase 6.1 decision #144)
- v2/v2-release-readiness.md — release-readiness tracker
- v2/phase-7-status.md — Phase 7 reconciliation: what shipped vs. the plan, and the five remaining gaps
- v2/implementation/phase--.md — per-phase execution plans with exit-gate evidence
v1 archive
The v1 in-process MXAccess architecture (Galaxy.Host + Galaxy.Proxy + Galaxy.Shared, .NET 4.8 x86 COM, the OtOpcUaGalaxyHost Windows service) was retired in PR 7.2 (2026-04-30, commit ae7106d). Docs that described that shape are kept under v1/ as historical record — see v1/README.md for the index.