feat: add workflow client updater for updating workflow client

src/Temporalio.Extensions.Hosting/README.md

@@ -99,4 +99,48 @@ start instead of expecting a `ITemporalClient` to be present on the service coll
 Some users may prefer to manually create the `TemporalWorker` without using host support, but still make their
 activities created via the service provider. `CreateTemporalActivityDefinitions` extension methods are present on
 `IServiceProvider` that will return a collection of `ActivityDefinition` instances for each activity on the type. These
-can be added to the `TemporalWorkerOptions` directly.
+can be added to the `TemporalWorkerOptions` directly.
+
+## Worker Client Refresh
+
+Some users may need to update the worker's connection to Temporal. It's desirable to do this without stopping the worker entirely, as that will evict the sticky workflow cache.
+
+This can be done by using the `IWorkerClientUpdater`.
+
+```csharp
+using Temporalio.Extensions.Hosting;
+
+var builder = Host.CreateApplicationBuilder(args);
+
+// Register a worker client updater.
+builder.Services.AddSingleton<TemporalWorkerClientUpdater>();
+
+// Add a hosted Temporal worker which returns a builder to add activities and workflows, along with the worker client updater.
+builder.Services.
+    AddHostedTemporalWorker(
+        "my-temporal-host:7233",
+        "my-namespace",
+        "my-task-queue").
+    AddScopedActivities<MyActivityClass>().
+    AddWorkflow<MyWorkflow>().
+    ConfigureOptions().
+    Configure<TemporalWorkerClientUpdater>((options, workerClientUpdater) => options.WorkerClientUpdater = workerClientUpdater);
+
+var host = builder.Build();
+
+// You can have a BackgroundService periodically refresh the worker client like this.
+TemporalWorkerClientUpdater workerClientUpdater = host.Services.GetRequiredService<TemporalWorkerClientUpdater>();
+
+// Can update the TLS options if you need.
+TemporalClientConnectOptions clientConnectOptions = new("my-other-temporal-host:7233")
+{
+    Namespace = "default"
+};
+
+ITemporalClient updatedClient = await TemporalClient.ConnectAsync(clientConnectOptions).ConfigureAwait(false);
+
+workerClientUpdater.UpdateClient(updatedClient);
+
+// Make sure you use RunAsync and not Run, see https://github.com/temporalio/sdk-dotnet/issues/220
+await host.RunAsync();
+```

src/Temporalio.Extensions.Hosting/TemporalWorkerClientUpdater.cs

@@ -0,0 +1,48 @@
+using System;
+using Temporalio.Worker;
+
+namespace Temporalio.Extensions.Hosting
+{
+    /// <summary>
+    /// Notification hub that can be used to push Temporal worker client updates to subscribing Temporal workers.
+    /// </summary>
+    public class TemporalWorkerClientUpdater
+    {
+        private readonly object clientLock = new();
+
+        private event EventHandler<IWorkerClient>? OnClientUpdatedEvent;
+
+        /// <summary>
+        /// Dispatches a notification to all subscribers that a new worker client should be used.
+        /// </summary>
+        /// <param name="client">The new <see cref="IWorkerClient"/> that should be pushed out to all subscribing workers.</param>
+        public void UpdateClient(IWorkerClient client)
+        {
+            OnClientUpdatedEvent?.Invoke(this, client);
+        }
+
+        /// <summary>
+        /// Adds a new subscriber that will be notified when a new worker client should be used.
+        /// </summary>
+        /// <param name="eventHandler">The event handler to add to the event listeners.</param>
+        internal void Subscribe(EventHandler<IWorkerClient> eventHandler)
+        {
+            lock (clientLock)
+            {
+                OnClientUpdatedEvent += eventHandler;
+            }
+        }
+
+        /// <summary>
+        /// Removes an existing subscriber from receiving notifications when a new worker client should be used.
+        /// </summary>
+        /// <param name="eventHandler">The event handler to remove from the event listeners.</param>
+        internal void Unsubscribe(EventHandler<IWorkerClient> eventHandler)
+        {
+            lock (clientLock)
+            {
+                OnClientUpdatedEvent -= eventHandler;
+            }
+        }
+    }
+}

src/Temporalio.Extensions.Hosting/TemporalWorkerService.cs

@@ -15,10 +15,11 @@ namespace Temporalio.Extensions.Hosting
     /// </summary>
     public class TemporalWorkerService : BackgroundService
     {
-        // These two are mutually exclusive
+        // These two (newClientOptions and existingClient) are mutually exclusive
         private readonly TemporalClientConnectOptions? newClientOptions;
         private readonly ITemporalClient? existingClient;
         private readonly TemporalWorkerOptions workerOptions;
+        private readonly TemporalWorkerClientUpdater? workerClientUpdater;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="TemporalWorkerService"/> class using
@@ -30,8 +31,11 @@ public class TemporalWorkerService : BackgroundService
         /// <param name="options">Options to use to create the worker service.</param>
         public TemporalWorkerService(TemporalWorkerServiceOptions options)
         {
-            newClientOptions = options.ClientOptions ?? throw new ArgumentException(
-                "Client options is required", nameof(options));
+            if (options.ClientOptions == null)
+            {
+                throw new ArgumentException("Client options is required", nameof(options));
+            }
+
             workerOptions = options;
         }
 
@@ -156,6 +160,11 @@ public TemporalWorkerService(
             if (newClientOptions != null && workerOptions.LoggerFactory != null)
             {
                 newClientOptions.LoggerFactory = workerOptions.LoggerFactory;
+            }
+
+            if (options.WorkerClientUpdater != null)
+            {
+                this.workerClientUpdater = options.WorkerClientUpdater;
             }
         }
 
@@ -166,7 +175,28 @@ protected override async Task ExecuteAsync(CancellationToken stoppingToken)
             // Call connect just in case it was a lazy client (no-op if already connected)
             await client.Connection.ConnectAsync().ConfigureAwait(false);
             using var worker = new TemporalWorker(client, workerOptions);
-            await worker.ExecuteAsync(stoppingToken).ConfigureAwait(false);
+
+            if (workerClientUpdater != null)
+            {
+                void SubscribeToClientUpdates(object? sender, IWorkerClient updatedClient)
+                {
+                    worker!.Client = updatedClient;
+                }
+
+                try
+                {
+                    workerClientUpdater.Subscribe(SubscribeToClientUpdates);
+                    await worker.ExecuteAsync(stoppingToken).ConfigureAwait(false);
+                }
+                finally
+                {
+                    workerClientUpdater.Unsubscribe(SubscribeToClientUpdates);
+                }
+            }
+            else
+            {
+                await worker.ExecuteAsync(stoppingToken).ConfigureAwait(false);
+            }
         }
     }
 }

src/Temporalio.Extensions.Hosting/TemporalWorkerServiceOptions.cs

@@ -31,6 +31,12 @@ public TemporalWorkerServiceOptions(string taskQueue)
         /// </summary>
         public TemporalClientConnectOptions? ClientOptions { get; set; }
 
+        /// <summary>
+        /// Gets or sets the <see cref="TemporalWorkerClientUpdater"/> that can be used to push Temporal worker client updates to the underlying <see cref="TemporalWorker"/>.
+        /// If not set, the worker service will not be updateable with a new Temporal worker client.
+        /// </summary>
+        public TemporalWorkerClientUpdater? WorkerClientUpdater { get; set; }
+
         /// <inheritdoc />
         public override object Clone()
         {
@@ -39,6 +45,7 @@ public override object Clone()
             {
                 options.ClientOptions = (TemporalClientConnectOptions)ClientOptions.Clone();
             }
+
             return options;
         }
 

src/Temporalio/Worker/TemporalWorker.cs

@@ -108,7 +108,7 @@ public TemporalWorker(IWorkerClient client, TemporalWorkerOptions options)
         /// </summary>
         /// <remarks>
         /// When this property is set, it actually replaces the underlying client that is being used
-        /// by the worker. This means the next calls by the worker to Temporal (e.g. responding
+        /// by the worker. This means subsequent calls by the worker to Temporal (e.g. responding
         /// task completion, activity heartbeat, etc) will be on this new client, but outstanding
         /// calls will not be immediately interrupted.
         /// </remarks>
@@ -255,6 +255,7 @@ protected virtual void Dispose(bool disposing)
             {
                 activityWorker?.Dispose();
                 BridgeWorker.Dispose();
+
                 // Remove task tracing if not disabled and there are workflows present
                 if (workflowTracingEventListenerEnabled)
                 {

tests/Temporalio.Tests/AssertMore.cs

@@ -1,11 +1,67 @@
 using System.Text;
 using System.Text.Json;
+using Temporalio.Api.History.V1;
+using Temporalio.Client;
 using Xunit;
 
 namespace Temporalio.Tests
 {
     public static class AssertMore
     {
+        public static Task TaskFailureEventuallyAsync(WorkflowHandle handle, Action<WorkflowTaskFailedEventAttributes> assert)
+        {
+            return AssertMore.EventuallyAsync(async () =>
+            {
+                WorkflowTaskFailedEventAttributes? attrs = null;
+                await foreach (var evt in handle.FetchHistoryEventsAsync())
+                {
+                    if (evt.WorkflowTaskFailedEventAttributes != null)
+                    {
+                        attrs = evt.WorkflowTaskFailedEventAttributes;
+                    }
+                }
+                Assert.NotNull(attrs);
+                assert(attrs!);
+            });
+        }
+
+        public static Task StartedEventuallyAsync(WorkflowHandle handle)
+        {
+            return HasEventEventuallyAsync(handle, e => e.WorkflowExecutionStartedEventAttributes != null);
+        }
+
+        public static async Task ChildStartedEventuallyAsync(WorkflowHandle handle)
+        {
+            // Wait for started
+            string? childId = null;
+            await HasEventEventuallyAsync(
+                handle,
+                e =>
+                {
+                    childId = e.ChildWorkflowExecutionStartedEventAttributes?.WorkflowExecution?.WorkflowId;
+                    return childId != null;
+                });
+            // Check that a workflow task has completed proving child has really started
+            await HasEventEventuallyAsync(
+                handle.Client.GetWorkflowHandle(childId!),
+                e => e.WorkflowTaskCompletedEventAttributes != null);
+        }
+
+        public static Task HasEventEventuallyAsync(WorkflowHandle handle, Func<HistoryEvent, bool> predicate)
+        {
+            return EventuallyAsync(async () =>
+            {
+                await foreach (var evt in handle.FetchHistoryEventsAsync())
+                {
+                    if (predicate(evt))
+                    {
+                        return;
+                    }
+                }
+                Assert.Fail("Event not found");
+            });
+        }
+
         public static Task EventuallyAsync(
             Func<Task> func, TimeSpan? interval = null, int iterations = 15) =>
             EventuallyAsync(

tests/Temporalio.Tests/Extensions/Hosting/TemporalWorkerServiceTests.cs

@@ -79,11 +79,11 @@ public async Task TemporalWorkerService_ExecuteAsync_SimpleWorker()
             // Add the rest of the services
             services.
                 AddSingleton<ILoggerFactory>(loggerFactory).
-                AddScoped<DatabaseClient>().
-                // We are also adding the DB client as a keyed service to demonstrate keyed service
-                // support for our DI logic. This used to break because newer DI library versions
-                // disallowed accessing certain properties on keyed services which we access
-                // internally for dupe checks.
+                AddScoped<DatabaseClient>().
+                // We are also adding the DB client as a keyed service to demonstrate keyed service
+                // support for our DI logic. This used to break because newer DI library versions
+                // disallowed accessing certain properties on keyed services which we access
+                // internally for dupe checks.
                 AddKeyedScoped<DatabaseClient>("client-keyed").
                 AddHostedTemporalWorker(taskQueue).
                 AddScopedActivities<DatabaseActivities>().
@@ -206,6 +206,84 @@ public async Task TemporalWorkerService_ExecuteAsync_MultipleWorkers()
                 ["scoped-other2"] = $"tq: {taskQueue2}, counter: 6",
             },
             result);
+    }
+
+    [Workflow]
+    public class TickingWorkflow
+    {
+        [WorkflowRun]
+        public async Task RunAsync()
+        {
+            // Just tick every 100ms for 10s
+            for (var i = 0; i < 100; i++)
+            {
+                await Workflow.DelayAsync(100);
+            }
+        }
+    }
+
+    [Fact]
+    public async Task TemporalWorkerService_WorkerClientReplacement_UsesNewClient()
+    {
+        // We are going to start a second ephemeral server and then replace the client. So we will
+        // start a no-cache ticking workflow with the current client and confirm it has accomplished
+        // at least one task. Then we will start another on the other client, and confirm it gets
+        // started too. Then we will terminate both. We have to use a ticking workflow with only one
+        // poller to force a quick re-poll to recognize our client change quickly (as opposed to
+        // just waiting the minute for poll timeout).
+        await using var otherEnv = await Temporalio.Testing.WorkflowEnvironment.StartLocalAsync();
+
+        // Start both workflows on different servers
+        var taskQueue = $"tq-{Guid.NewGuid()}";
+        var handle1 = await Client.StartWorkflowAsync(
+            (TickingWorkflow wf) => wf.RunAsync(),
+            new(id: $"workflow-{Guid.NewGuid()}", taskQueue));
+        var handle2 = await otherEnv.Client.StartWorkflowAsync(
+            (TickingWorkflow wf) => wf.RunAsync(),
+            new(id: $"workflow-{Guid.NewGuid()}", taskQueue));
+
+        var bld = Host.CreateApplicationBuilder();
+
+        TemporalWorkerClientUpdater workerClientUpdater = new TemporalWorkerClientUpdater();
+
+        // Register the worker client updater.
+        bld.Services.AddSingleton<TemporalWorkerClientUpdater>(workerClientUpdater);
+
+        // Add the first worker with the workflow and client already DI'd, and add the worker client updater.
+        bld.Services.
+            AddSingleton(Client).
+            AddHostedTemporalWorker(taskQueue).
+            AddWorkflow<TickingWorkflow>()
+            .ConfigureOptions()
+            .Configure<TemporalWorkerClientUpdater>((options, updater) =>
+            {
+                options.WorkerClientUpdater = updater;
+                options.MaxCachedWorkflows = 0;
+                options.MaxConcurrentWorkflowTaskPolls = 1;
+            });
+
+        // Start the host
+        using var tokenSource = new CancellationTokenSource();
+        using var host = bld.Build();
+        var hostTask = Task.Run(() => host.RunAsync(tokenSource.Token));
+
+        // Confirm the first ticking workflow has completed a task but not the second workflow
+        await AssertMore.HasEventEventuallyAsync(handle1, e => e.WorkflowTaskCompletedEventAttributes != null);
+        await foreach (var evt in handle2.FetchHistoryEventsAsync())
+        {
+            Assert.Null(evt.WorkflowTaskCompletedEventAttributes);
+        }
+
+        // Now replace the client, which should be used fairly quickly because we should have
+        // timer-done poll completions every 100ms
+        workerClientUpdater.UpdateClient(otherEnv.Client);
+
+        // Now confirm the other workflow has started
+        await AssertMore.HasEventEventuallyAsync(handle2, e => e.WorkflowTaskCompletedEventAttributes != null);
+
+        // Terminate both
+        await handle1.TerminateAsync();
+        await handle2.TerminateAsync();
     }
 
     [Workflow("Workflow")]