Instruction file imported from opendsc/opendsc (.github/instructions/lcm.instructions.md). Copyright stays with the author.

LCM Service (OpenDsc.Lcm)

Cross-platform .NET background service that continuously monitors and/or remediates DSC configurations.

Key Components

Operational Modes

• Monitor — periodically runs dsc config test to detect drift, logs results
• Remediate — runs dsc config test then applies dsc config set when drift detected

Configuration Model

public class LcmConfig
{
    public ConfigurationMode ConfigurationMode { get; set; } = ConfigurationMode.Monitor;
    public ConfigurationSource ConfigurationSource { get; set; } = ConfigurationSource.Local;
    public string ConfigurationPath { get; set; }          // Path to main.dsc.yaml (Local mode)
    public TimeSpan ConfigurationModeInterval { get; set; } = TimeSpan.FromMinutes(15);
    public string? DscExecutablePath { get; set; }         // Defaults to 'dsc' in PATH
    public PullServerSettings? PullServer { get; set; }    // Pull mode only
}

Configuration Priority (highest wins)

1. Command-line arguments
2. Environment variables (prefix LCM_)
3. System-wide config file:
   • Windows: %ProgramData%\OpenDSC\LCM\appsettings.json
   • Linux: /etc/opendsc/lcm/appsettings.json
   • macOS: /Library/Preferences/OpenDSC/LCM/appsettings.json
4. Bundled appsettings.json in service directory
5. appsettings.{Environment}.json

Key Patterns

Dynamic mode switching — watches for config changes, gracefully switches without restart:

_configChangeToken = lcmMonitor.OnChange((config, name) => {
    OnConfigurationReloaded(config);  // Cancels current operation, switches mode
});

DSC execution:

var result = await dscExecutor.ExecuteTestAsync(config.ConfigurationPath, config, LogLevel.Information);
// Returns DscResult with messages, results[], hadErrors

Logging — uses LoggerMessage source-generated attributes for performance. All log messages are defined as partial methods in worker classes.

Pull Mode Flow

1. Load/generate client certificate (CertificateSource: Managed auto-generates; Platform loads from store by thumbprint)
2. Register node if not already registered → receives NodeId
3. Check certificate expiry → rotate via RotateCertificateAsync() if needed
4. Check configuration checksum → download if changed
5. Execute dsc config test; apply dsc config set if Remediate mode and drift found
6. Submit compliance report if ReportCompliance: true

Pull Server Configuration

{
  "LCM": {
    "ConfigurationSource": "Pull",
    "PullServer": {
      "ServerUrl": "https://pull-server.example.com",
      "RegistrationKey": "shared-secret",
      "NodeId": null,
      "ReportCompliance": true,
      "CertificateSource": "Managed",
      "CertificateRotationInterval": "60.00:00:00",
      "CertificatePath": "{ConfigDir}/certs/client.pfx"
    }
  }
}

Local Testing

$env:LCM_ConfigurationPath = "C:\configs\local\main.dsc.yaml"
$env:LCM_ConfigurationMode = "Monitor"
$env:LCM_ConfigurationModeInterval = "00:05:00"
.\artifacts\Lcm\OpenDsc.Lcm.exe