lmxopcua/docs/OpcUaServer.md

OPC UA Server

The OPC UA server component hosts the Galaxy-backed namespace on a configurable TCP endpoint and exposes deployed System Platform objects and attributes to OPC UA clients.

Configuration

OpcUaConfiguration defines the server endpoint and session settings. All properties have sensible defaults:

Property	Default	Description
Port	4840	TCP port the server listens on
EndpointPath	/LmxOpcUa	URI path appended to the base address
ServerName	LmxOpcUa	Application name presented to clients
GalaxyName	ZB	Galaxy name used in the namespace URI
MaxSessions	100	Maximum concurrent client sessions
SessionTimeoutMinutes	30	Idle session timeout
AlarmTrackingEnabled	false	Enables AlarmConditionState nodes for alarm attributes

The resulting endpoint URL is opc.tcp://0.0.0.0:{Port}{EndpointPath}, e.g., opc.tcp://0.0.0.0:4840/LmxOpcUa.

The namespace URI follows the pattern urn:{GalaxyName}:LmxOpcUa and serves as both the ApplicationUri and ProductUri.

Programmatic ApplicationConfiguration

OpcUaServerHost builds the entire ApplicationConfiguration in code. There are no XML configuration files. This keeps deployment simple on factory floor machines where editing XML is error-prone.

The configuration covers:

• ServerConfiguration -- base address, session limits, security policies, and user token policies
• SecurityConfiguration -- certificate store paths under %LOCALAPPDATA%\OPC Foundation\pki\, auto-accept enabled
• TransportQuotas -- 4 MB max message/string/byte-string size, 120-second operation timeout, 1-hour security token lifetime
• TraceConfiguration -- OPC Foundation SDK tracing is disabled (output path null, trace masks 0); all logging goes through Serilog instead

Security Policy

The server runs with MessageSecurityMode.None and SecurityPolicies.None:

SecurityPolicies = { new ServerSecurityPolicy
{
    SecurityMode = MessageSecurityMode.None,
    SecurityPolicyUri = SecurityPolicies.None
} }

This is intentional for plant-floor deployments where the server sits on an isolated OT network. Galaxy-level security classification controls write access per attribute rather than at the transport layer.

User token policies

UserTokenPolicies are dynamically configured based on the Authentication settings in appsettings.json:

• An Anonymous user token policy is added when AllowAnonymous is true (the default).
• A UserName user token policy is added when the Users list contains at least one entry.

Both policies can be active simultaneously, allowing clients to connect with or without credentials.

Session impersonation

When a client presents UserName credentials, the server validates them through IUserAuthenticationProvider. If the credentials do not match any entry in the configured Users list, the session is rejected.

On successful validation, the session identity is set to a RoleBasedIdentity that carries the user's granted role IDs. Authenticated users receive the WellKnownRole_AuthenticatedUser role. Anonymous connections receive the WellKnownRole_Anonymous role. These roles are used downstream by the write override to enforce AnonymousCanWrite restrictions.

Certificate handling

On startup, OpcUaServerHost.StartAsync calls CheckApplicationInstanceCertificate(false, 2048) to locate or create a 2048-bit self-signed certificate. The certificate subject follows the format CN={ServerName}, O=ZB MOM, DC=localhost. Certificate stores use the directory-based store type under %LOCALAPPDATA%\OPC Foundation\pki\:

Store	Path suffix
Own	pki/own
Trusted issuers	pki/issuer
Trusted peers	pki/trusted
Rejected	pki/rejected

AutoAcceptUntrustedCertificates is set to true so the server does not reject client certificates.

Server class hierarchy

LmxOpcUaServer extends StandardServer

LmxOpcUaServer inherits from the OPC Foundation StandardServer base class and overrides two methods:

• CreateMasterNodeManager -- Instantiates LmxNodeManager with the Galaxy namespace URI, the IMxAccessClient for runtime I/O, performance metrics, and an optional HistorianDataSource. The node manager is wrapped in a MasterNodeManager with no additional core node managers.
• LoadServerProperties -- Returns server metadata: manufacturer ZB MOM, product LmxOpcUa Server, and the assembly version as the software version.

Session tracking

LmxOpcUaServer exposes ActiveSessionCount by querying ServerInternal.SessionManager.GetSessions().Count. OpcUaServerHost surfaces this for status reporting.

Startup and Shutdown

OpcUaServerHost.StartAsync performs the following sequence:

1. Build ApplicationConfiguration programmatically
2. Validate the configuration via appConfig.Validate(ApplicationType.Server)
3. Create ApplicationInstance and check/create the application certificate
4. Instantiate LmxOpcUaServer and start it via ApplicationInstance.Start

OpcUaServerHost.Stop calls _server.Stop() and nulls both the server and application instance references. The class implements IDisposable, delegating to Stop.

Key source files

• src/ZB.MOM.WW.LmxOpcUa.Host/OpcUa/OpcUaServerHost.cs -- Application lifecycle and programmatic configuration
• src/ZB.MOM.WW.LmxOpcUa.Host/OpcUa/LmxOpcUaServer.cs -- StandardServer subclass and node manager creation
• src/ZB.MOM.WW.LmxOpcUa.Host/Configuration/OpcUaConfiguration.cs -- Configuration POCO