UA-.NETStandard/docs/MigrationGuide.md

Migration Guide

This document is the landing page for migrating your application between versions of the OPC UA .NET Standard Stack. The detailed per-version content lives in the migrate/ sub-folder; this page is the index that points you at the right version folder and keeps the small legacy migration notes inline.

General principles

1. All API that is replaced with newer API is marked [Obsolete] and code should compile and work albeit of the warnings (which can be suppressed). [Obsolete] API will be cleaned up in the next minor version increment. We therefore recommend upgrading from minor version to minor version and fixing all [Obsolete] warnings as you go along.
2. API that cannot be supported anymore will be removed in a minor version and migration steps documented in the version sub-folder. We try to keep this to an absolute minimum.
3. Bugs or issues found in obsoleted API are not supported.
4. We follow semver, but do not use the major version indicator to denote breaking changes like (1) or (2) as we should if we followed related conventions. We are a small team and cannot afford to maintain previous major versions, therefore we try to keep cases of (2) to a minimum and expect you to upgrade to the next minor version within 6 months of release.

Pro TIP. Point your favourite coding agent at this guide and let it do the migration work for you. The opcua-v20-migration agent skill knows when to load which sub-doc and runs the migration-analyzer codefixer end-to-end.

Per-version migration index

From	To	Where to read
1.5.378	2.0.x	migrate/2.0.x/ — landing page + 13 thematic sub-docs (telemetry, packages, source-generation, types, encoders, node-states, identity, certificates, configuration, sessions-subscriptions, pubsub, alarms-model-change, timeprovider).
1.05.377	1.05.378	§ inline below — small enough to keep on this page.
1.04	1.05	§ inline below — small enough to keep on this page.

Looking for the broader narrative (non-prescriptive overview of what changed in a release)? See What's New in 2.0.

Migrating code that used the exposed diagnostics locks

IServerInternal, ISession and ISubscription no longer expose their synchronization primitives. The removed members are:

Interface	Removed
IServerInternal	DiagnosticsLock, DiagnosticsWriteLock
ISession	DiagnosticsLock
ISubscription	DiagnosticsLock, DiagnosticsWriteLock

A caller could not reason about these locks: it could not see what else took them, in what order, or for how long, and holding one across a call back into the stack could deadlock. Each owner now applies the mutation itself, so the critical section stays inside the object that understands it.

// was
lock (server.DiagnosticsLock)
{
    server.ServerDiagnostics.RejectedSessionCount++;
}

// now
server.UpdateServerDiagnostics(diagnostics => diagnostics.RejectedSessionCount++);

The same shape applies to sessions and subscriptions:

session.UpdateDiagnostics(diagnostics => diagnostics.ClientLastContactTime = now);
subscription.UpdateDiagnostics(diagnostics => diagnostics.NextSequenceNumber = next);

To read a value derived from the session or subscription diagnostics, use the read counterpart, which holds the same lock for the duration of the projection:

uint count = session.ReadDiagnostics(diagnostics => diagnostics.RepublishRequestCount);

Do not let the diagnostics object escape the callback. Once the callback returns the lock is released, so any field read from a captured reference is unsynchronized. Project the values you need inside the callback and return those.

IServerInternal.ServerDiagnostics was removed for the same reason: it handed out the mutable structure that the lock protects. UpdateServerDiagnostics and the diagnostic node manager are the supported paths.

Analyzer UA0024 flags each removed member and names its replacement. It reports rather than auto-fixes: turning a lock statement body into a lambda is not a transformation that can be applied safely without understanding what the body captures and returns.

Why there is no [Obsolete] shim

Every other removal in this guide keeps an [Obsolete] member for a release. These do not, and deliberately so. A lock is only useful if it is the lock the owner takes. A shim would have to hand back either a lock nobody else takes - silently turning a working critical section into no synchronization at all - or the real lock, which is exactly the coupling being removed. A missing member is a compile error the analyzer explains; a shim would be a race that shows up in production. ISession and ISubscription are also implemented by downstream code, and re-adding an interface member would break every implementer.

Migrating code that used ILocalNode.DataLock

ILocalNode.DataLock (implemented by Node) was removed. It returned the node instance itself, so lock (node.DataLock) was lock (node): one lock shared between the stack, the node and every caller, taken in an order none of them could see.

// was
lock (node.DataLock)
{
    value = node.Value;
}

// now - the node guards its own state
value = node.Value;

If the surrounding operation has to stay atomic across several calls, take a lock the calling component owns. Do not reach for one that is reachable from a shared node. Analyzer UA0025 flags the removed member.

Migrating code that used BaseVariableValue.Lock

BaseVariableValue.Lock was removed, and the constructor now takes a System.Threading.Lock instead of an object.

A derived value class - which is what the source generator emits for every structure variable - synchronizes through the protected EnterLock() / ExitLock() pair:

EnterLock();
try
{
    // read or write the value fields
}
finally
{
    ExitLock();
}

A component that has to make its own state atomic with the value passes a lock it already owns to the constructor and takes that one directly. This is how the server keeps its status and its diagnostics mutually exclusive:

private readonly Lock m_diagnosticsLock = new();

// the value is constructed with the lock its owner already holds elsewhere
m_status = new ServerStatusValue(statusNode, status, m_diagnosticsLock);

// so the owner synchronizes against the value without the value handing anything out
lock (m_diagnosticsLock)
{
    ...
}

Analyzer UA0026 flags the removed member. Note that regenerating the model sources with the 2.0 generator produces the EnterLock() / ExitLock() form already, so this only affects hand-written derived value classes and callers.

Migrating code that locked on a NodeState or a NodeBrowser

A NodeState guards its own attributes, children, notifiers and references, and NodeState.CreateBrowser guards the browser it builds. Nothing in the stack takes a lock on a node instance any more, so neither should a caller:

// was — the node manager reached for the node's monitor from outside the node
lock (source)
{
    browser = source.CreateBrowser(context, view, referenceType, includeSubtypes,
        browseDirection, default, null, false);
}

// now
INodeBrowser browser = source.CreateBrowser(context, view, referenceType,
    includeSubtypes, browseDirection, default, null, false);

lock (node) was also the only way to make a check-then-act pair atomic. Use NodeState.AddReferenceIfMissing instead, which does the check and the insert under the node's own lock:

// was
lock (node)
{
    if (!node.ReferenceExists(ReferenceTypeIds.HasNotifier, true, ObjectIds.Server))
    {
        node.AddReference(ReferenceTypeIds.HasNotifier, true, ObjectIds.Server);
    }
}

// now
node.AddReferenceIfMissing(ReferenceTypeIds.HasNotifier, true, ObjectIds.Server);

NodeBrowser.DataLock is gone with it. A browser is single-consumer: it belongs to whoever created it and performs no synchronization of its own. A derived browser that took DataLock inside its Next() override drops the lock statement and keeps the body. Where a browser genuinely outlives one service call — the instance parked in a continuation point for BrowseNext — its owner serializes it, as the stack does for its own continuation points.

A node type that overrides CreateBrowser and builds its own browser instead of delegating to the base implementation must fill it through PopulateBrowserSynchronized rather than calling PopulateBrowser directly, otherwise its browser is assembled from separately locked reads and can observe a node halfway through a change.

Analyzer UA0027 flags NodeBrowser.DataLock. See migrate/2.0.x/node-states.md.

Migrating code that used ApplicationConfiguration.PropertiesLock

ApplicationConfiguration.PropertiesLock was removed. It returned the properties dictionary itself, so lock (configuration.PropertiesLock) was lock (configuration.Properties): the lock was the data it guarded, shared between the configuration and every caller, taken in an order none of them could see.

Properties is now a concurrent dictionary, so each individual operation is already atomic and most callers simply drop the lock:

// was
lock (configuration.PropertiesLock)
{
    configuration.Properties["MyKey"] = value;
}

// now
configuration.Properties["MyKey"] = value;

The one combination that needs more than a single operation is get-or-add, which has its own member:

// was
lock (configuration.PropertiesLock)
{
    if (configuration.Properties.TryGetValue("MyKey", out object? existing))
    {
        return (MyType)existing;
    }
    var created = Build();
    configuration.Properties["MyKey"] = created;
    return created;
}

// now
return configuration.GetOrAddProperty("MyKey", Build);

GetOrAddProperty deliberately does not invoke the factory under a lock, so a caller cannot hold a critical section across a callback. Under contention the factory may run more than once; only one result is published and every caller receives that same instance, so keep the factory free of side effects that would matter if it ran twice.

One behaviour change is worth knowing: enumerating Properties while another thread writes no longer throws InvalidOperationException. It yields a moment-in-time view instead. Code that relied on the exception to detect concurrent modification has to detect it some other way.

Analyzer UA0028 flags the removed member.

Migrating node types that override FindChild or CreateChild

NodeState.FindChild and NodeState.CreateChild take assignInstanceNodeIds as their last parameter, and the four argument FindChild / two argument CreateChild virtuals are gone. The parameter defaults to true, so call sites are unaffected; an override fails to compile (CS0115) until the parameter is added and passed on.

Behaviour note: a node copy — NodeState.Create(context, source) and the Initialize(ISystemContext, NodeState) path behind it — now passes assignInstanceNodeIds: false. It no longer asks ISystemContext.NodeIdFactory for identifiers that the copy overwrites from the source on the very next statement. If your INodeIdFactory counts, reserves or audits every allocation, expect fewer calls than in 1.5.378 for the same address space; the resulting NodeIds are unchanged. Any NodeState subclass you own must thread the argument into its CreateOrReplace<Child> calls to get that benefit.

See Node states § FindChild and CreateChild for the before/after and Custom node types and assignment control for the runtime rules.

Removed members on ISession

ISession.SessionDiagnostics is removed. It handed out the whole mutable SessionDiagnosticsDataType — the structure the session's diagnostics lock protects — so a caller could read a field while the owner was writing it.

Every server-side reader wanted one value out of it, and those two values are now on the interface directly:

// was
string? uri = session.SessionDiagnostics?.ClientDescription?.ApplicationUri;
string name = session.SessionDiagnostics?.SessionName ?? string.Empty;

// now
string? uri = session.ClientApplicationUri;
string name = session.SessionName;

For anything else in the structure, project it inside ReadDiagnostics, which holds the lock for the duration of the projection:

uint reads = session.ReadDiagnostics(diagnostics => diagnostics.ReadCount.TotalCount);

SessionName is read from the field it was always a copy of rather than from the diagnostics, because it is assigned once during construction and a value that cannot change should not cost a lock.

The concrete Session still exposes SessionDiagnostics; only the interface loses it.

ISession.ValidateBeforeActivate — the synchronous overload with out IUserIdentityTokenHandler? and out UserTokenPolicy? parameters — is removed. It had no caller anywhere in the stack, its samples or its tests other than tests written for it, and it had been [Obsolete] since 1.5.378.

Use ValidateBeforeActivateAsync, which returns the same two values as a tuple:

(IUserIdentityTokenHandler identityToken, UserTokenPolicy? userTokenPolicy) =
    await session.ValidateBeforeActivateAsync(
        context, clientSignature, userIdentityToken, userTokenSignature, ct)
    .ConfigureAwait(false);

The synchronous overload could not verify a user token that required decryption, so on a secure endpoint it failed closed and directed callers to the asynchronous path anyway.

The history continuation points moved off ISession onto ISession.ContinuationPoints, and no longer pass object. SaveHistory and RestoreHistory use IHistoryContinuationPoint, which carries the point's own Guid Id and extends IDisposable:

// was
session.SaveHistoryContinuationPoint(state.Id, state);
object? restored = session.RestoreHistoryContinuationPoint(bytes);

// now
session.ContinuationPoints.SaveHistory(state);   // the point carries its Id
IHistoryContinuationPoint? restored = session.ContinuationPoints.RestoreHistory(bytes);

Implement IHistoryContinuationPoint on whatever type you store. The session previously disposed only those points that happened to implement IDisposable and silently leaked the rest; every point is now disposed.

Migrating code that called IServerInternal.Set* mutators

IServerInternal no longer exposes the twelve Set* binding methods or CreateServerObjectAsync. They were startup plumbing: StandardServer calls each exactly once, in one block, to carry a Create* factory result into the datastore. Publishing them on the interface let any holder rewire a running server, which would leave every component that had already resolved a subsystem holding the previous instance.

The supported seam is the factory seam, which already existed for every subsystem here:

Instead of	Override	Or register in DI
SetRoleManager	StandardServer.CreateRoleManager	IRoleManager
SetUserManagement	StandardServer.CreateUserManagement (new)	IUserManagement
SetMonitoredItemQueueFactory	StandardServer.CreateMonitoredItemQueueFactory	IMonitoredItemQueueFactory
SetSubscriptionStore	StandardServer.CreateSubscriptionStore	ISubscriptionStore
SetMainNodeManagerFactory	StandardServer.CreateMainNodeManagerFactory	—
SetNodeManager	StandardServer.CreateMasterNodeManager	—
SetSessionManager	StandardServer.CreateSessionManager / CreateSubscriptionManager	ISessionManager, ISubscriptionManager
SetAggregateManager	StandardServer.CreateAggregateManagerAsync	—
SetModellingRulesManager	StandardServer.CreateModellingRulesManagerAsync	—
SetConformanceUnitsManager	StandardServer.CreateConformanceUnitsManagerAsync	—

CreateUserManagement is new in this release, because user management was the one subsystem with no factory seam. Registering an IUserManagement in the container also switches on the username/password authenticator; override CreateUserManagement if you want the Part 18 §5 model without that.

SetIdentityRegistry is removed with no replacement. Nothing ever called it: the supported route has always been ServerIdentityRegistryExtensions.RegisterDefaultAuthenticators, which adds authenticators to the default registry rather than replacing it.

The methods remain on the concrete ServerInternalData, so code that already held that type keeps compiling. Binding is now refused once the server has finished starting — a late Set* throws ServiceResultException with BadInvalidState naming the operation.

Migrating IServerStartupTask implementations to IServerContext

IServerStartupTask.OnServerStartedAsync now receives an IServerContext instead of an IServerInternal. IServerInternal derives from IServerContext, so the host still passes the same object; only the declared parameter type changes and an implementation fails to compile (CS0535) until its signature is updated.

IServerContext is the ambient view of a running server. It carries what is genuinely server-wide and nothing else — it deliberately does not hand out the server's subsystems. A startup task that needs a subsystem takes it as a constructor dependency, which every implementation in this repository already did for its other dependencies.

Rewrite the member reads that no longer resolve:

Was	Now
server.Telemetry	server.DefaultSystemContext.Telemetry
server.NamespaceUris	server.DefaultSystemContext.NamespaceUris
server.ServerUris	server.DefaultSystemContext.ServerUris
server.TypeTree	server.DefaultSystemContext.TypeTable
server.Factory	server.DefaultSystemContext.EncodeableFactory
server.DiagnosticsNodeManager.FindPredefinedNode<T>(id)	server.FindPredefinedNode<T>(id)
server.NodeManager.NodeManagers + a type test	server.FindNodeManagers<TCapability>()
server.SessionManager, server.SubscriptionManager, server.RequestManager, server.AggregateManager, server.RoleManager, server.IdentityRegistry, …	constructor injection

server.MessageContext is unchanged and remains on IServerContext. Do not substitute server.DefaultSystemContext.AsMessageContext() for it: that conversion produces a context with default decoding limits rather than the server's configured MaxStringLength, MaxArrayLength and MaxByteStringLength, which silently widens what your component accepts.

Tests that hand a Mock<IServerInternal> to a startup task keep compiling, because the mock still satisfies IServerContext. Stub the members the task actually reads now — typically DefaultSystemContext and any FindNodeManagers<T>() — or the mock returns null and the task fails at run time rather than at build time.

Removed members on IServerInternal

The following members had no consumer anywhere in the stack, its samples or its tests, and have been removed. Each has a direct replacement:

Removed	Use instead
CloseSession(OperationContext, NodeId, bool)	CloseSessionAsync(…)
Status	CurrentState to read, UpdateServerStatus to write
ServerDiagnostics	UpdateServerDiagnostics(Action<…>)
DiagnosticsEnabled	IDiagnosticsNodeManager.DiagnosticsEnabled
ModellingRulesManager, ConformanceUnitsManager	the concrete ServerInternalData, which owns them

MessageContext, DefaultSystemContext, CurrentState, ServerObject, ReportEventAsync, CloseSessionAsync, DeleteSubscriptionAsync and UpdateServerDiagnostics all moved down to IServerContext, the ambient view of a running server that IServerInternal now derives from. They remain reachable through IServerInternal unchanged, so no call site has to move. CurrentState is read-only on the ambient interface; the server itself still sets it.

Migrating servers that relied on unserved history advertisement

Server startup now reconciles variables that advertise history with the historian providers actually wired into the server. If a variable has Historizing=true or HistoryRead / HistoryWrite access-level bits from a NodeSet but no IHistorianProvider resolves for it, the server clears the advertisement and masks the attribute read callbacks before accepting clients. Variables with a provider keep their NodeSet-declared history surface.

If a client or CTT setup expected HistoryRead solely because the NodeSet declared it, wire a historian instead of relying on the static flag: use builder.UseHistorian() and .Historize(...), register a provider through the server-wide historian registry, or override GetHistorianProvider(NodeState) in the node manager. See Server address-space metadata and Historical Access.

Migrating custom ISessionManager implementations to ShutdownAsync

ISessionManager.Shutdown() is gone, replaced by ShutdownAsync(CancellationToken). SessionManager previously started its session monitor loop with a discarded Task.Factory.StartNew(...), so Shutdown() only signalled the loop and returned: the server could finish tearing down while the monitor was still closing expired sessions and raising keep-alive events against half-disposed state. There is no correct synchronous way to wait for that loop — blocking on it would be sync-over-async — so the synchronous overload was removed rather than kept as a trap. ShutdownAsync cancels the loop and awaits it before disposing the sessions, matching ISubscriptionManager.ShutdownAsync.

Callers await instead of calling:

// before
server.SessionManager.Shutdown();

// after
await server.SessionManager.ShutdownAsync(cancellationToken)
    .ConfigureAwait(false);

Implementers of ISessionManager (for example a manager registered through services.AddSessionManager<T>()) replace Shutdown with ShutdownAsync. If your implementation has no background work, return a completed task:

public ValueTask ShutdownAsync(CancellationToken cancellationToken = default)
{
    CloseAllSessions();
    return default;
}

Deriving from SessionManager requires no change beyond renaming any Shutdown override: ShutdownAsync is virtual and the base implementation already awaits the monitor loop.

Migrating callers of the synchronous MonitoredNode2 notification wrappers

MonitoredNode2.OnReportEvent and MonitoredNode2.OnMonitoredNodeChanged are [Obsolete]; use OnReportEventAsync and OnMonitoredNodeChangedAsync. Nothing in the stack wires the synchronous pair any more — notifiers are attached through NodeState.OnReportEventAsync and NodeState.OnStateChangedAsync — and both wrappers block the calling thread whenever the bounded notification channel is full, or whenever the node has an asynchronous read handler. Blocking there occupies a thread while waiting for a consumer that needs a thread of its own, which starves the thread pool under load.

// before
monitoredNode.OnReportEvent(context, node, e);

// after
await monitoredNode.OnReportEventAsync(context, node, e, cancellationToken)
    .ConfigureAwait(false);

The wrappers still work and are unchanged in behaviour, so this is a warning to act on rather than a break.

Migrating from 1.05.377 to 1.05.378

Asynchronous as default

The server now supports AsyncNodeManagers; see Server Async (TAP) Support. The client APIs are async by default and all synchronous and APM-based API has been deprecated. To migrate, update your code to use the Async version of every API where possible. Not recommended but for expedience you can call the Async version synchronously with GetAwaiter().GetResult().

Observability

Observability is now plumbed through ITelemetryContext. The legacy static Utils.SetLogger / Utils.Trace* model has been removed in 2.0. See migrate/2.0.x/telemetry.md for OLD vs NEW snippets, the per-type constructor matrix, and the full inventory of removed / [Obsolete] Utils APIs.

Configuration-level trace apply APIs were removed as well: TraceConfiguration.ApplySettings() and ApplicationConfigurationBuilder trace setters (SetOutputFilePath, SetDeleteOnLoad, SetTraceMasks). Configure logging through ITelemetryContext instead.

Migrating from 1.04 to 1.05

A few features are still missing to fully comply with 1.05, but certification for v1.04 is still possible with the 1.05 release.

Support

For additional migration support:

• Review sample applications in the repository.
• Check unit tests for usage patterns.
• Use the OPCFoundation.NetStandard.Opc.Ua.MigrationAnalyzer package — analyzer rules UA0001-UA0020 map to the patterns in migrate/2.0.x/types.md and apply most edits via a code-fixer.
• Open an issue on OPCFoundation/UA-.NETStandard.