# Gateway Configuration

This document describes every option bound under the `MxGateway` configuration
section by `GatewayOptions`.

The gateway binds configuration at startup and validates it with
`GatewayOptionsValidator`. Startup fails before the server listens when required
paths, timeouts, queue sizes, enum values, or protocol values are invalid.

## Configuration Shape

```json
{
  "MxGateway": {
    "Authentication": {
      "Mode": "ApiKey",
      "SqlitePath": "C:\\ProgramData\\MxGateway\\gateway-auth.db",
      "PepperSecretName": "MxGateway:ApiKeyPepper",
      "RunMigrationsOnStartup": true
    },
    "Worker": {
      "ExecutablePath": "src\\MxGateway.Worker\\bin\\x86\\Release\\MxGateway.Worker.exe",
      "WorkingDirectory": null,
      "RequiredArchitecture": "X86",
      "StartupTimeoutSeconds": 30,
      "StartupProbeRetryAttempts": 3,
      "StartupProbeRetryDelayMilliseconds": 250,
      "PipeConnectAttemptTimeoutMilliseconds": 2000,
      "ShutdownTimeoutSeconds": 10,
      "HeartbeatIntervalSeconds": 5,
      "HeartbeatGraceSeconds": 15,
      "MaxMessageBytes": 16777216
    },
    "Sessions": {
      "DefaultCommandTimeoutSeconds": 30,
      "MaxSessions": 64,
      "MaxPendingCommandsPerSession": 128,
      "DefaultLeaseSeconds": 1800,
      "LeaseSweepIntervalSeconds": 30,
      "AllowMultipleEventSubscribers": false
    },
    "Events": {
      "QueueCapacity": 10000,
      "BackpressurePolicy": "FailFast"
    },
    "Dashboard": {
      "Enabled": true,
      "PathBase": "/dashboard",
      "RequireAdminScope": true,
      "AllowAnonymousLocalhost": true,
      "SnapshotIntervalMilliseconds": 1000,
      "RecentFaultLimit": 100,
      "RecentSessionLimit": 200,
      "ShowTagValues": false
    },
    "Protocol": {
      "WorkerProtocolVersion": 1,
      "MaxGrpcMessageBytes": 16777216
    },
    "Galaxy": {
      "ConnectionString": "Server=localhost;Database=ZB;Integrated Security=True;TrustServerCertificate=True;Encrypt=False;",
      "CommandTimeoutSeconds": 60,
      "DashboardRefreshIntervalSeconds": 30
    },
    "Alarms": {
      "Enabled": false,
      "SubscriptionExpression": "",
      "DefaultArea": "",
      "ReconcileIntervalSeconds": 30
    }
  }
}
```

Environment variables use the normal .NET double-underscore form. For example,
`MxGateway__Sessions__MaxSessions=20` overrides
`MxGateway:Sessions:MaxSessions`.

## Authentication Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Authentication:Mode` | `ApiKey` | Selects public gRPC authentication. Supported values are `ApiKey` and `Disabled`. `Disabled` bypasses API-key verification and is for local development only. |
| `MxGateway:Authentication:SqlitePath` | `C:\ProgramData\MxGateway\gateway-auth.db` | SQLite database path for API-key records and audit rows when API-key authentication is enabled. |
| `MxGateway:Authentication:PepperSecretName` | `MxGateway:ApiKeyPepper` | Configuration key used to read the HMAC pepper for API-key secret hashing. The dashboard effective configuration redacts this value. |
| `MxGateway:Authentication:RunMigrationsOnStartup` | `true` | Runs SQLite auth schema migrations at gateway startup when API-key authentication is enabled. |

When `Mode` is `ApiKey`, `SqlitePath` and `PepperSecretName` must be present.
`SqlitePath` must be a valid filesystem path.

## Worker Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Worker:ExecutablePath` | `src\MxGateway.Worker\bin\x86\Release\MxGateway.Worker.exe` | Path to the x86 worker executable launched for each gateway session. The path must be valid and point to a `.exe` file. |
| `MxGateway:Worker:WorkingDirectory` | `null` | Optional working directory for the worker process. When set, it must be a valid filesystem path. |
| `MxGateway:Worker:RequiredArchitecture` | `X86` | Required Portable Executable architecture for the worker. Supported values are `X86` and `X64`; MXAccess parity uses `X86`. |
| `MxGateway:Worker:StartupTimeoutSeconds` | `30` | Total startup budget for process launch, startup probe, pipe connect, handshake, and worker readiness. |
| `MxGateway:Worker:StartupProbeRetryAttempts` | `3` | Number of retry attempts for transient worker startup probe failures before pipe connection and handshake continue. |
| `MxGateway:Worker:StartupProbeRetryDelayMilliseconds` | `250` | Delay between transient startup probe retry attempts. |
| `MxGateway:Worker:PipeConnectAttemptTimeoutMilliseconds` | `2000` | Per-attempt timeout used by the worker named-pipe connect retry path. The overall pipe connection still stays under the startup budget. |
| `MxGateway:Worker:ShutdownTimeoutSeconds` | `10` | Grace period for worker shutdown before the gateway treats shutdown as failed and may kill the worker process tree. |
| `MxGateway:Worker:HeartbeatIntervalSeconds` | `5` | Worker heartbeat send interval and gateway heartbeat check cadence input. |
| `MxGateway:Worker:HeartbeatGraceSeconds` | `15` | Maximum age of the last worker heartbeat before the gateway faults the worker. This must be greater than or equal to `HeartbeatIntervalSeconds`. |
| `MxGateway:Worker:MaxMessageBytes` | `16777216` | Maximum worker IPC frame payload size in bytes. The validator allows values from `1024` through `268435456`. |

`StartupProbeRetryAttempts`, `StartupProbeRetryDelayMilliseconds`,
`PipeConnectAttemptTimeoutMilliseconds`, timeout values, heartbeat values, and
`MaxMessageBytes` must be positive. `MaxMessageBytes` is intentionally bounded
to avoid accidental large allocations from malformed or oversized frames.

## Session Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Sessions:DefaultCommandTimeoutSeconds` | `30` | Default timeout used while the gateway waits for a worker command reply when an open-session request does not provide a positive command timeout. |
| `MxGateway:Sessions:MaxSessions` | `64` | Maximum number of concurrently open gateway sessions. Session opens reserve a slot atomically before worker creation. |
| `MxGateway:Sessions:MaxPendingCommandsPerSession` | `128` | Maximum number of pending worker commands for one session. Excess commands fail fast instead of queueing indefinitely. |
| `MxGateway:Sessions:DefaultLeaseSeconds` | `1800` | Initial session lease and refresh duration. Unary client activity extends the lease by this duration. |
| `MxGateway:Sessions:LeaseSweepIntervalSeconds` | `30` | Hosted monitor interval for closing expired leases. Active event-stream subscribers keep a session from expiring while the stream remains attached. |
| `MxGateway:Sessions:AllowMultipleEventSubscribers` | `false` | Controls whether multiple `StreamEvents` subscribers may attach to one session. `true` is rejected until event fan-out is implemented. |

All numeric session options must be greater than zero. The current event stream
implementation supports one active subscriber per session; this preserves event
ordering and avoids competing consumers.

## Event Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Events:QueueCapacity` | `10000` | Capacity for bounded per-session event queues used by the gateway worker event channel and the public gRPC event stream queue. |
| `MxGateway:Events:BackpressurePolicy` | `FailFast` | Event backpressure behavior. `FailFast` faults the session on public stream queue overflow. `DisconnectSubscriber` disconnects only the slow stream. |

`QueueCapacity` must be greater than zero. With `FailFast`, queue overflow
faults the affected worker or session instead of silently dropping MXAccess
events. With `DisconnectSubscriber`, public gRPC stream overflow terminates only
the affected stream while the MXAccess session remains active.

## Dashboard Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Dashboard:Enabled` | `true` | Enables Blazor Server dashboard route mapping. |
| `MxGateway:Dashboard:PathBase` | `/dashboard` | Base path for dashboard routes. When the dashboard is enabled, this value is required and must start with `/`. |
| `MxGateway:Dashboard:RequireAdminScope` | `true` | Requires API keys used for dashboard login to carry the `admin` scope. |
| `MxGateway:Dashboard:AllowAnonymousLocalhost` | `true` | Allows loopback dashboard requests to bypass the dashboard cookie requirement for local development. Remote requests still require dashboard authentication. |
| `MxGateway:Dashboard:SnapshotIntervalMilliseconds` | `1000` | Dashboard snapshot refresh interval used by realtime Blazor pages. |
| `MxGateway:Dashboard:RecentFaultLimit` | `100` | Maximum number of fault summaries projected into each dashboard snapshot. |
| `MxGateway:Dashboard:RecentSessionLimit` | `200` | Maximum number of session summaries projected into each dashboard snapshot. |
| `MxGateway:Dashboard:ShowTagValues` | `false` | Reserved display control for tag values. The dashboard does not show full tag values by default. |

`SnapshotIntervalMilliseconds` must be greater than zero. `RecentFaultLimit`
and `RecentSessionLimit` must be greater than or equal to zero.

## Protocol Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Protocol:WorkerProtocolVersion` | `1` | Worker IPC protocol version expected by the gateway and worker. This must match `GatewayContractInfo.WorkerProtocolVersion`. |
| `MxGateway:Protocol:MaxGrpcMessageBytes` | `16777216` | Public gRPC max send and receive message size in bytes. The same default is used by official clients. The validator allows values from `1024` through `268435456`. |

The protocol option is exposed for diagnostics and explicit deployment
configuration, not for compatibility negotiation. A mismatch fails validation
at startup.

## Galaxy Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Galaxy:ConnectionString` | `Server=localhost;Database=ZB;Integrated Security=True;TrustServerCertificate=True;Encrypt=False;` | SQL Server connection string for the Galaxy Repository (`ZB`) used by the `GalaxyRepository` browse RPCs. Override in production via `MxGateway__Galaxy__ConnectionString`. |
| `MxGateway:Galaxy:CommandTimeoutSeconds` | `60` | Per-command SQL timeout for all Galaxy browse RPCs. |
| `MxGateway:Galaxy:DashboardRefreshIntervalSeconds` | `30` | Interval between background refreshes of the dashboard Galaxy summary cache. SQL is hit at most once per interval regardless of dashboard render rate. |

See [Galaxy Repository Browse](./GalaxyRepository.md) for the RPC surface and
behavior.

## Alarm Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Alarms:Enabled` | `false` | Gates the gateway's always-on central alarm monitor. When `true`, the gateway opens one gateway-owned worker session dedicated to alarms, caches the active-alarm set, and fans it out to every client through the `StreamAlarms` RPC — no client opens its own session to see alarms. |
| `MxGateway:Alarms:SubscriptionExpression` | _(empty)_ | AVEVA alarm-subscription expression the monitor subscribes on startup, in canonical `\\<machine>\Galaxy!<area>` form. The literal `Galaxy` provider is correct regardless of the Galaxy database name. When empty and `Enabled` is `true`, the gateway falls back to `\\<MachineName>\Galaxy!<DefaultArea>` if `DefaultArea` is set. |
| `MxGateway:Alarms:DefaultArea` | _(empty)_ | Area name used to compose a default subscription when `SubscriptionExpression` is empty. If both are empty while `Enabled` is `true`, the monitor faults with a configuration diagnostic. |
| `MxGateway:Alarms:ReconcileIntervalSeconds` | `30` | How often the monitor reconciles its in-process alarm cache against the worker's authoritative active-alarm snapshot, catching transitions the live poll-and-diff feed missed. Floored at 5 seconds. |

The alarm monitor is independent of client sessions: `AcknowledgeAlarm` and
`StreamAlarms` are session-less RPCs served by the monitor. See
[Alarm Client Discovery](./AlarmClientDiscovery.md) for the AVEVA consumer
surface the monitor's worker session drives.

## Related Documentation

- [Gateway Process Detailed Design](./GatewayProcessDesign.md)
- [Gateway Dashboard Detailed Design](./GatewayDashboardDesign.md)
- [Worker Process Launcher](./WorkerProcessLauncher.md)
- [Worker Frame Protocol](./WorkerFrameProtocol.md)
- [Galaxy Repository Browse](./GalaxyRepository.md)