Runtime NodeSets

This guide explains how to load one or more NodeSet2 XML documents into the server's address space at startup without writing a source-generated or hand-coded NodeManager. You configure which files or streams to load; the server imports them in dependency order and registers the resulting nodes.

When to use the runtime NodeSet path

Use AddRuntimeNodeSet when:

• You receive a NodeSet2 XML from a companion-specification vendor and want to host its nodes without regenerating source.
• Your information model changes frequently enough that rebuilding the source-generated manager for every XML update would be disruptive.
• You are prototyping or testing a new NodeSet2 design.

Use the source-generated path when you want compile-time safety, strong typing, and AOT-safe named constants for every node in your model. The runtime path gives you generic NodeState objects and untyped browse-path wiring.

Startup and live lifecycle semantics

AddRuntimeNodeSet on IOpcUaServerBuilder remains the startup path: its factory is created before the server starts and its NodeSet is imported during CreateAddressSpaceAsync.

Running servers also expose INodeManagerLifecycle. Resolve it from dependency injection in a hosted server, or use StandardServer.NodeManagerLifecycle when constructing the server directly. The lifecycle provider can add, reload, shadow-reload, and remove runtime NodeSets without restarting the server.

public sealed class ModelLoader(INodeManagerLifecycle lifecycle)
{
    private NodeManagerRegistration? m_registration;

    public async ValueTask LoadAsync(CancellationToken ct)
    {
        m_registration = await lifecycle.AddRuntimeNodeSetAsync(
            new RuntimeNodeSetOptions
            {
                Sources = [RuntimeNodeSetSource.FromFile("Models/MyMachine.NodeSet2.xml")]
            },
            callerContext: null,
            ct);
    }

    public async ValueTask ReloadAsync(CancellationToken ct)
    {
        m_registration = await lifecycle.ReloadRuntimeNodeSetAsync(
            m_registration!,
            new RuntimeNodeSetOptions
            {
                Sources = [RuntimeNodeSetSource.FromFile("Models/MyMachine.NodeSet2.xml")]
            },
            callerContext: null,
            ct);
    }

    public ValueTask RemoveAsync(CancellationToken ct)
    {
        return lifecycle.RemoveAsync(m_registration!, callerContext: null, ct);
    }
}

Each add returns an immutable NodeManagerRegistration, and reload returns the next generation while invalidating the previous handle.

AddRuntimeNodeSetAsync, ReloadRuntimeNodeSetAsync, and RemoveAsync take the operation the caller is running under. Pass context.GetOperationContext() when calling from a NodeManager or Method callback: a lifecycle operation drains the requests that are in flight, so one started from inside a request would wait for itself and is rejected with an InvalidOperationException. A control-plane caller such as the ModelLoader above is not serving a request and passes null. See Registering NodeManagers.

The rules that apply to every NodeManager registered at runtime -- what happens to MonitoredItems, Browse continuation points, namespace indexes, DataTypes, and change notifications, and which NodeManagers may be reloaded at all -- are described once in Registering NodeManagers. Runtime NodeSets follow those rules, and the built-in runtime NodeSet manager already implements the INodeManagerReloadParticipant contract that reload requires.

Shadow reload

ShadowReloadRuntimeNodeSetAsync (backed by INodeManagerLifecycle.ShadowReloadAsync) replaces a live registration the same way ReloadRuntimeNodeSetAsync does, but without the active-monitored-item guard:

public async ValueTask ShadowReloadAsync(CancellationToken ct)
{
    m_registration = await lifecycle.ShadowReloadRuntimeNodeSetAsync(
        m_registration!,
        new RuntimeNodeSetOptions
        {
            Sources = [RuntimeNodeSetSource.FromFile("Models/MyMachine.NodeSet2.xml")]
        },
        ct);
}

The replacement generation is prepared and published through the same transactional prepare/publish/commit/rollback path as ReloadAsync, so a failure during preparation, publication, or the routing switch leaves the current generation fully active and cleans up the replacement, exactly as a normal reload does. Once committed, every new service request is atomically routed to the replacement generation, including for namespaces the current and replacement generations share.

The current generation is not torn down immediately. It is moved to the same retired-generation bookkeeping used for an ordinary reload, but its existing monitored items and any request or continuation point that already captured it keep being served by it, unaffected by the routing switch. The retired generation is disposed automatically, without deleting any client subscription, once its monitored items and in-flight state drain; a later lifecycle operation (or shutdown) opportunistically retries that cleanup until it succeeds. ShadowReloadAsync returns the replacement NodeManagerRegistration immediately and invalidates the current handle for further lifecycle mutations, the same as ReloadAsync.

Use ShadowReloadAsync when a model update must take effect for new requests without waiting for existing subscriptions to unsubscribe first; use the fail-closed ReloadAsync when a stale generation must never remain reachable, even briefly, for already-open monitored items.

Immediate reload

ImmediateReloadRuntimeNodeSetAsync (backed by INodeManagerLifecycle.ImmediateReloadAsync) performs the same atomic replacement but does not retain the previous generation until monitored items drain. After requests that already captured the old routing generation finish, every affected data-change monitored item is made publishable with BadNodeIdUnknown, event monitored items stop producing events, continuation points are invalidated, and the old NodeManager is disposed. The subscription and monitored-item records remain available so clients can receive the status and delete or recreate the affected items.

Use immediate reload only when continuity through the previous generation is not required. Durable monitored items are not eligible for immediate retirement because their terminal state would have to survive restart; choose shadow reload for any generation that owns them.

Quick-start examples

Single file

services.AddOpcUa()
    .AddServer(o => { /* … */ })
    .AddRuntimeNodeSet("Models/MyMachine.NodeSet2.xml");

Single file with a fluent callback

Wire read/write/method handlers on top of the imported nodes using the existing untyped INodeManagerBuilder surface:

services.AddOpcUa()
    .AddServer(o => { /* … */ })
    .AddRuntimeNodeSet(
        "Models/MyMachine.NodeSet2.xml",
        nodes =>
        {
            nodes.Node("Machines/Machine1/Start")
                .OnCall(StartMachineAsync);

            nodes.Variable<double>("Machines/Machine1/Temperature")
                .OnRead(ReadTemperature);
        });

Group of dependent NodeSets

Register multiple NodeSet2 sources that depend on each other. The factory resolves the import order automatically from the RequiredModel declarations in each document.

services.AddOpcUa()
    .AddServer(o => { /* … */ })
    .AddRuntimeNodeSet(options =>
    {
        options.Sources =
        [
            RuntimeNodeSetSource.FromFile("Models/Opc.Ua.Di.NodeSet2.xml"),
            RuntimeNodeSetSource.FromFile("Models/MyMachine.NodeSet2.xml")
        ];
        options.DefaultNamespaceUri = "urn:example:MyMachine";
        options.Configure = nodes =>
        {
            nodes.Node("Machines/Machine1/Start").OnCall(StartMachineAsync);
        };
    });

Custom stream source

Use RuntimeNodeSetSource.FromStream when you want to open the NodeSet2 document lazily — for example from a database, a blob store, or an assembly resource. The delegate is called for each startup load or live generation and must return a fresh, readable Stream each time.

services.AddOpcUa()
    .AddServer(o => { /* … */ })
    .AddRuntimeNodeSet(options =>
    {
        options.Sources =
        [
            RuntimeNodeSetSource.FromStream(
                name: "MyMachine",
                openStream: ct => OpenNodeSetStreamAsync(ct),
                modelNamespaceUris: ["urn:example:MyMachine"])
        ];
    });

Direct factory registration

If you prefer to create the factory manually — for example to inject it into an existing StandardServer subclass — construct a RuntimeNodeSetNodeManagerFactory directly:

var factory = new RuntimeNodeSetNodeManagerFactory(new RuntimeNodeSetOptions
{
    Sources = [RuntimeNodeSetSource.FromFile("Models/MyMachine.NodeSet2.xml")]
});

// In a StandardServer subclass constructor:
AddNodeManager(factory);

Stream ownership contract

When FromStream is used, the runtime loader calls the openStream delegate while each NodeManager generation is created and closes the returned stream after deserialization. You must ensure that:

1. Each call to openStream returns a new stream positioned at the beginning.
2. The stream is readable and contains a valid NodeSet2 XML document.
3. You do not close the stream yourself; the factory disposes it after UANodeSet.Read.

If the delegate returns null or the stream does not contain valid NodeSet2 XML, server startup fails with a clear InvalidOperationException that names the source.

Default namespace for unqualified browse paths

When the Configure callback uses browse paths without an explicit ns=N; prefix (for example "Machines/Machine1/Start"), the runtime loader must know which namespace index to apply for the first path segment. The resolution is:

1. If RuntimeNodeSetOptions.DefaultNamespaceUri is set, that URI is used.
2. Otherwise the factory infers the unique leaf model — the one model in the loaded group that is not required by any other included source.
3. If inference is ambiguous (multiple leaf models and a Configure callback is present), startup fails with an error message that lists the candidates. In this case, set DefaultNamespaceUri explicitly.

When no Configure callback is registered, DefaultNamespaceUri has no effect and may be omitted.

Dependency sorting

The factory reads the Models/Model/RequiredModel entries from each parsed NodeSet document and performs a topological sort (Kahn's algorithm) before importing. Import order guarantees that a required model's nodes are in the address space before any document that depends on them imports its nodes.

Dependencies on models not included in the group — for example the OPC UA base namespace or a third-party model hosted by a generated NodeManager — are silently allowed and treated as external. The server resolves cross-manager references through the normal AddReverseReferencesAsync mechanism.

Cycles among the included sources cause InvalidOperationException at startup with an error message that lists the participating sources.

Complex types

Runtime complex type loading (structures, enumerations, union types) is on by default and requires no extra configuration. After all NodeManagers have built their address spaces, StandardServer.OnNodeManagerStartedAsync scans every DataType node whose DataTypeDefinition attribute is populated and registers a NativeAOT-safe stand-in encodeable in the server's factory. The same stand-ins are reused for client decode/encode via the OPC UA Part 6 binary protocol.

You can tune this behaviour through the existing ServerComplexTypeOptions:

services.AddOpcUa()
    .AddServer(o => { /* … */ })
    .AddRuntimeNodeSet("Models/MyMachine.NodeSet2.xml")
    .AddComplexTypeSystem(o => o.Enabled = false); // disable if not needed

Setting StandardServer.LoadComplexTypes = false or disabling the complex type system entirely suppresses the stand-in loading without producing a warning. No second complex-type loading path is introduced by the runtime NodeSet feature.

For a complete description of the server-side complex type system, see ComplexTypes.md.

Comparison with source-generated NodeManagers

Aspect	Runtime NodeSet (AddRuntimeNodeSet)	Source-generated ([NodeManager])
Node access in callbacks	Generic NodeState / BaseVariableState via untyped browse paths	Strongly typed, compiler-checked fluent accessors per node
Compilation required on model change	No — reload through INodeManagerLifecycle	Yes — regenerate and rebuild
AOT / trimming compatibility	Full (uses the existing UANodeSet.Read XmlSerializer path)	Full (generated code is static)
Named NodeId constants	Not generated	Generated (Variables.*, Objects.*, etc.)
Multiple namespaces in one manager	Yes — group multiple sources	One namespace per generator run
DI registration	AddRuntimeNodeSet(...)	AddNodeManager<TFactory>()
Stream / file input	Files and custom stream factories	MSBuild AdditionalFiles only

Source-generated managers are the recommended path for production code where type safety and compile-time validation matter. Runtime NodeSets are the recommended path for rapid prototyping, model-file delivery scenarios, and cases where the XML content changes independently of the server binary.

Related documentation

• Source-Generated NodeManagers — strongly typed alternative.
• Dependency Injection — IOpcUaServerBuilder and service registration.
• ComplexTypes.md — server-side complex type loading and client-side decoding.