SCADA System — Design Documentation
Overview
This document serves as the master index for the SCADA system design. The system is a centrally-managed, distributed SCADA configuration and deployment platform built on Akka.NET, running across a central cluster and multiple site clusters in a hub-and-spoke topology.
Technology Stack
| Layer | Technology |
|---|---|
| Runtime | .NET, Akka.NET (actors, clustering, remoting, persistence, streams) |
| Central UI | Blazor Server (ASP.NET Core + SignalR) |
| Inbound API | ASP.NET Core Web API (REST/JSON) |
| Central Database | MS SQL Server, Entity Framework Core |
| Site Storage | SQLite (deployed configs, S&F buffer, event logs) |
| Authentication | Direct LDAP/AD bind (LDAPS/StartTLS), JWT sessions |
| Notifications | SMTP with OAuth2 Client Credentials (Microsoft 365) |
| Hosting | Windows Server, Windows Service |
| Cluster | Akka.NET Cluster (active/standby, keep-oldest SBR) |
| Logging | Serilog (structured) |
Scale
- ~10 site clusters, each with 50–500 machines, 25–75 live tags per machine.
- Central cluster: 2-node active/standby behind a load balancer.
- Site clusters: 2-node active/standby, headless (no UI).
Document Map
Requirements
- HighLevelReqs.md — Complete high-level requirements covering all functional areas.
Component Design Documents
| # | Component | Document | Description |
|---|---|---|---|
| 1 | Template Engine | Component-TemplateEngine.md | Template modeling, inheritance, composition, path-qualified member addressing, override granularity, locking, alarms, flattening, semantic validation, revision hashing, and diff calculation. |
| 2 | Deployment Manager | Component-DeploymentManager.md | Central-side deployment pipeline with deployment ID/idempotency, per-instance operation lock, state transition matrix, all-or-nothing site apply, system-wide artifact deployment with per-site status. |
| 3 | Site Runtime | Component-SiteRuntime.md | Site-side actor hierarchy with explicit supervision strategies, staggered startup, script trust model (constrained APIs), Tell/Ask conventions, concurrency serialization, and site-wide Akka stream with per-subscriber backpressure. |
| 4 | Data Connection Layer | Component-DataConnectionLayer.md | Common data connection interface (OPC UA, custom), Become/Stash connection actor model, auto-reconnect, immediate bad quality on disconnect, transparent re-subscribe, synchronous write failures, tag path resolution retry. |
| 5 | Central–Site Communication | Component-Communication.md | Akka.NET remoting/cluster topology, 8 message patterns with per-pattern timeouts, application-level correlation IDs, transport heartbeat config, message ordering, connection failure behavior. |
| 6 | Store-and-Forward Engine | Component-StoreAndForward.md | Buffering (transient failures only), fixed-interval retry, parking, async best-effort replication, SQLite persistence at sites. |
| 7 | External System Gateway | Component-ExternalSystemGateway.md | HTTP/REST + JSON, API key/Basic Auth, per-system timeout, dual call modes (Call/CachedCall), transient/permanent error classification, dedicated blocking I/O dispatcher, ADO.NET connection pooling. |
| 8 | Notification Service | Component-NotificationService.md | SMTP with OAuth2 (M365) or Basic Auth, BCC delivery, plain text, transient/permanent SMTP error classification, store-and-forward integration. |
| 9 | Central UI | Component-CentralUI.md | Blazor Server with SignalR real-time push, load balancer failover with JWT, all management workflows. |
| 10 | Security & Auth | Component-Security.md | Direct LDAP bind (LDAPS/StartTLS), JWT sessions (HMAC-SHA256, 15-min refresh, 30-min idle), role-based authorization, site-scoped permissions. |
| 11 | Health Monitoring | Component-HealthMonitoring.md | 30s report interval, 60s offline threshold, monotonic sequence numbers, raw error counts, tag resolution counts, dead letter monitoring. |
| 12 | Site Event Logging | Component-SiteEventLogging.md | SQLite storage, 30-day retention + 1GB cap, daily purge, paginated remote queries with keyword search. |
| 13 | Cluster Infrastructure | Component-ClusterInfrastructure.md | Akka.NET cluster, keep-oldest SBR with down-if-alone, min-nr-of-members=1, 2s/10s/15s failure detection, CoordinatedShutdown, automatic dual-node recovery. |
| 14 | Inbound API | Component-InboundAPI.md | POST /api/{methodName}, X-API-Key header, flat JSON, extended type system (Object/List), script-based implementations, failures-only logging. |
| 15 | Host | Component-Host.md | Single deployable binary, role-based component registration, per-component config binding (Options pattern), readiness gating, dead letter monitoring, Akka.NET bootstrap, ASP.NET Core hosting for central. |
| 16 | Commons | Component-Commons.md | Namespace/folder convention (Types/Interfaces/Entities/Messages), shared data types, POCOs, repository interfaces, message contracts with additive-only versioning, UTC timestamp convention. |
| 17 | Configuration Database | Component-ConfigurationDatabase.md | EF Core data access, per-component repositories, unit-of-work, optimistic concurrency on deployment status, audit logging (IAuditService), migration management. |
| 18 | Management Service | Component-ManagementService.md | Akka.NET ManagementActor on central, ClusterClientReceptionist registration, programmatic access to all admin operations, CLI interface. |
| 19 | CLI | Component-CLI.md | Standalone command-line tool, System.CommandLine, Akka.NET ClusterClient transport, LDAP auth, JSON/table output, mirrors all Management Service operations. |
Reference Documentation
- AkkaDotNet/ — Akka.NET reference notes covering actors, remoting, clustering, persistence, streams, serialization, hosting, testing, and best practices.
- docs/plans/ — Design decision documents from refinement sessions.
Architecture Diagram (Logical)
Users (Blazor Server)
│
Load Balancer
│
┌────────────────────────┼────────────────────────────┐
│ CENTRAL CLUSTER │
│ (2-node active/standby) │
│ │
│ ┌──────────┐ ┌──────────┐ ┌──────────┐ │
│ │ Template │ │Deployment│ │ Central │ │
│ │ Engine │ │ Manager │ │ UI │ Blazor Svr │
│ └──────────┘ └──────────┘ └──────────┘ │
│ ┌──────────┐ ┌──────────┐ ┌──────────┐ │
│ │ Security │ │ Config │ │ Health │ │
│ │ & Auth │ │ DB │ │ Monitor │ │
│ │ (JWT/LDAP)│ │ (EF+IAud)│ │ │ │
│ └──────────┘ └──────────┘ └──────────┘ │
│ ┌──────────┐ │
│ │ Inbound │ ◄── External Systems (X-API-Key) │
│ │ API │ POST /api/{method}, JSON │
│ └──────────┘ │
│ ┌──────────┐ │
│ │ Mgmt │ ◄── CLI (ClusterClient) │
│ │ Service │ ManagementActor + Receptionist │
│ └──────────┘ │
│ ┌───────────────────────────────────┐ │
│ │ Akka.NET Communication Layer │ │
│ │ (correlation IDs, per-pattern │ │
│ │ timeouts, message ordering) │ │
│ └──────────────┬────────────────────┘ │
│ ┌──────────────┴────────────────────┐ │
│ │ Configuration Database (EF) │──► MS SQL │
│ └───────────────────────────────────┘ (Config DB)│
│ │ Machine Data DB│
└─────────────────┼───────────────────────────────────┘
│ Akka.NET Remoting
┌────────────┼────────────┐
▼ ▼ ▼
┌─────────┐ ┌─────────┐ ┌─────────┐
│ SITE A │ │ SITE B │ │ SITE N │
│ (2-node)│ │ (2-node)│ │ (2-node)│
│ ┌─────┐ │ │ ┌─────┐ │ │ ┌─────┐ │
│ │Data │ │ │ │Data │ │ │ │Data │ │
│ │Conn │ │ │ │Conn │ │ │ │Conn │ │
│ │Layer │ │ │ │Layer │ │ │ │Layer │ │
│ ├─────┤ │ │ ├─────┤ │ │ ├─────┤ │
│ │Site │ │ │ │Site │ │ │ │Site │ │
│ │Runtm│ │ │ │Runtm│ │ │ │Runtm│ │
│ ├─────┤ │ │ ├─────┤ │ │ ├─────┤ │
│ │S&F │ │ │ │S&F │ │ │ │S&F │ │
│ │Engine│ │ │ │Engine│ │ │ │Engine│ │
│ ├─────┤ │ │ ├─────┤ │ │ ├─────┤ │
│ │ExtSys│ │ │ │ExtSys│ │ │ │ExtSys│ │
│ │Gatwy │ │ │ │Gatwy │ │ │ │Gatwy │ │
│ └─────┘ │ │ └─────┘ │ │ └─────┘ │
│ SQLite │ │ SQLite │ │ SQLite │
└─────────┘ └─────────┘ └─────────┘
│ │ │
OPC UA / OPC UA / OPC UA /
Custom Custom Custom
Protocol Protocol Protocol
Site Runtime Actor Hierarchy
Deployment Manager Singleton (Cluster Singleton)
├── Instance Actor (one per deployed, enabled instance)
│ ├── Script Actor (coordinator, one per instance script)
│ │ └── Script Execution Actor (short-lived, per invocation)
│ ├── Alarm Actor (coordinator, one per alarm definition)
│ │ └── Alarm Execution Actor (short-lived, per on-trigger invocation)
│ └── ... (more Script/Alarm Actors)
├── Instance Actor
│ └── ...
└── ... (more Instance Actors)
Site-Wide Akka Stream (attribute + alarm state changes)
├── All Instance Actors publish to the stream
└── Debug view subscribes with instance-level filtering