# Service Hosting (v2)

## Overview

A production OtOpcUa deployment runs **one binary per node**, plus the optional Wonderware historian sidecar:

| Process | Project | Runtime | Platform | Responsibility |
|---|---|---|---|---|
| **OtOpcUa Host** | `src/Server/ZB.MOM.WW.OtOpcUa.Host` | .NET 10 | AnyCPU | Single fused binary. `OTOPCUA_ROLES` env decides what to mount: `admin` (Blazor + auth + control-plane singletons), `driver` (OPC UA endpoint + per-driver actors), or both. |
| **OtOpcUa Wonderware Historian** *(optional)* | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware` | .NET Framework 4.8 | x86 (32-bit) | Out-of-process sidecar exposing the Wonderware Historian SDK over a named pipe. Required only when `Historian:Wonderware:Enabled=true`. |

Galaxy access still uses the separately-installed **mxaccessgw** sidecar (see `docs/v2/Galaxy.ParityRig.md`); the gateway owns the MXAccess COM bitness constraint (its worker is x86 net48). Nothing in the OtOpcUa repo carries that constraint anymore.

> **v2 change.** v1's separate `OtOpcUa.Server` + `OtOpcUa.Admin` Windows services merged into a single role-gated `OtOpcUa.Host` binary. Two installers became one (with a `-Roles` parameter). The whole DI graph is composed in `OtOpcUa.Host/Program.cs`; per-role wiring is conditional on the env var.

## Role gating

`Program.cs` reads `OTOPCUA_ROLES`, parses it with `RoleParser`, and conditionally registers services:

| Role present | Wires |
|---|---|
| `admin` | `AddOtOpcUaAuth`, `AddAdminUI`, `AddSignalR`, `AddOtOpcUaAdminClients`, `MapOtOpcUaAuth`, `MapAdminUI<App>`, `MapOtOpcUaHubs`, `WithOtOpcUaControlPlaneSingletons` (5 admin singletons via `Akka.Hosting`) |
| `driver` | `WithOtOpcUaRuntimeActors` (DriverHostActor + DbHealthProbeActor) — and the OPC UA endpoint on port 4840 |
| Either / both | `AddOtOpcUaConfigDb`, `AddOtOpcUaCluster`, `AddOtOpcUaHealth` (`/health/ready`, `/health/active`, `/healthz`) |

Single-node dev: `OTOPCUA_ROLES=admin,driver`. Production: typically two admin nodes (HA pair) + N driver nodes.

### Per-role configuration overlays

`Program.cs:33-35` builds a role suffix by joining the parsed roles **alphabetically** with `-` and loads `appsettings.{roleSuffix}.json` as an optional overlay on top of base `appsettings.json`. Three overlays ship in `src/Server/ZB.MOM.WW.OtOpcUa.Host/`:

- `appsettings.admin.json` — admin-only nodes
- `appsettings.driver.json` — driver-only nodes
- `appsettings.admin-driver.json` — fused single-node dev / small deployments

All three carry Serilog log-level overrides + `Security:Ldap:DevStubMode = false`. Loading order is **base `appsettings.json` → role overlay (`appsettings.{role}.json`) → environment overlay (`appsettings.{Environment}.json`)** — later layers win. Overlays are optional; the base file boots a node on its own.

## Akka cluster

The host joins an Akka.NET cluster bound to the address in `appsettings.json::Cluster`:

```json
{
  "Cluster": {
    "Hostname": "0.0.0.0",
    "Port": 4053,
    "PublicHostname": "node-a.lan",
    "SeedNodes": ["akka.tcp://otopcua@node-a.lan:4053"],
    "Roles": ["admin", "driver"]
  }
}
```

- `WithOtOpcUaClusterBootstrap` (in `OtOpcUa.Cluster`) loads the embedded HOCON (split-brain resolver, pinned dispatcher, failure detector tuning) and overlays remote endpoint + cluster options.
- All cluster singletons + per-node actors live on this single ActorSystem — there is no second Akka instance.

See [Redundancy.md](Redundancy.md) for the role-leader + ServiceLevel story.

## Health endpoints

Both admin and driver nodes expose:

| Path | Status meaning |
|---|---|
| `/healthz` | Process alive. |
| `/health/ready` | ConfigDb reachable + cluster member state is `Up`. |
| `/health/active` | Admin-role leader (the node Traefik or an HA LB should route traffic to). |

Used by Traefik for the active-leader-only routing pattern (see [Task 63 traefik docs](v2/Architecture-v2.md) — TODO).

## OtOpcUa Wonderware Historian (optional)

Unchanged from v1. Pipe IPC contract lives in `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Client/Contracts/`; sidecar pipe handler in `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Pipe/`. Install via `scripts/install/Install-Services.ps1 -InstallWonderwareHistorian`.

## Install / Uninstall

- `scripts/install/Install-Services.ps1 -Roles admin,driver` — installs `OtOpcUaHost`. v2 rewrite tracked as plan Task 62.
- `scripts/install/Uninstall-Services.ps1` — stops + removes the host service (and the historian sidecar if installed).

## Logging

Serilog with rolling-daily file sinks. Each host writes to `logs/otopcua-*.log` plus stdout (NSSM/systemd-friendly). Per-environment log level overrides go in `appsettings.{Environment}.json`.

## Depth reference

For the full host-architecture rationale (why fused vs. split, role-gating tradeoffs, multi-node deployment shapes), see `docs/plans/2026-05-26-akka-hosting-alignment-design.md` §3-4.
