.Net-Core 2.2 MassTransit.ConfigurationException: The state machine was not properly configured

Question

Newbie question - what am I missing? Are there any dotnetcore 2.2 Saga examples available?

I have a basic end to end system working OK with messages flowing across containers in docker-compose, but adding a Saga seems to be a challenge -

Q. Am I missing a scheduler dependency? In MassTransit 5.5.5, cfg.UseInMemoryMessageScheduler(); doesn't compile.

Something odd was going on, I had to mark my state machine explicitly as ISaga

MassTransit.ConfigurationException: Failed to create the state machine connector for Model.WorkflowExecutionStateMachine ---> MassTransit.ConfigurationException: The state machine was not properly configured: workflowapi_1 | [Failure] ExecutingTask was not specified

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

        // Register MassTransit
        services.AddMassTransit(x =>
        {
            x.AddConsumer<WorkflowTaskConsumer>();

            // required?
            x.AddSaga<WorkflowExecutionSaga>();

            x.AddBus(provider => Bus.Factory.CreateUsingRabbitMq(cfg =>
            {
                var rabbitMQHostName = $"rabbitmq://{configuration["RabbitMQHostName"]}";

                Console.Out.WriteLineAsync($"Starting Workflow Receiver... {rabbitMQHostName}/{QueueNames.ExeuteWorkflowTaskQueue}");

                var host = cfg.Host(new Uri(rabbitMQHostName), hostConfig =>
                {
                    hostConfig.Username("guest");
                    hostConfig.Password("guest");
                });

                // A basic message works OK
                cfg.ReceiveEndpoint(host, QueueNames.ExeuteWorkflowTaskQueue, ep =>
                {
                    ep.PrefetchCount = 1;
                    ep.UseMessageRetry(mr => mr.Interval(1000, 2));
                    ep.ConfigureConsumer<WorkflowTaskConsumer>(provider);
                });

                // Doesn't like this
                cfg.ReceiveEndpoint(host, QueueNames.WorkflowStateMachineSagaQueueName, ep =>
                {
                    ep.PrefetchCount = 1;
                    ep.UseMessageRetry(mr => mr.Interval(1000, 2));
                    ep.StateMachineSaga(new WorkflowExecutionSaga(), new InMemorySagaRepository<WorkflowExecutionStateMachine>());
                });
            }));

            cfg.UseInMemoryMessageScheduler(); // doesn't compile!
        });
    }

Bus is started as follows -

    public void Configure(IApplicationBuilder app, IHostingEnvironment env, IApplicationLifetime lifetime)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            // The default HSTS value is 30 days. You may want to change this for production scenarios, 
            // see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }

        app.UseMvc();

        var bus = app.ApplicationServices.GetService<IBusControl>();
        var busHandle = TaskUtil.Await(() =>
        {
            return bus.StartAsync();
        });

        lifetime.ApplicationStopping.Register(() =>
        {
            busHandle.Stop();
        });
    }

Exception details are

Unhandled Exception: MassTransit.ConfigurationException: Failed to create the state machine connector for Rapid.Workflow.Api.Model.WorkflowExecutionStateMachine ---> MassTransit.ConfigurationException: The state machine was not properly configured: workflowapi_1 | [Failure] ExecutingTask was not specified workflowapi_1 | at Automatonymous.StateMachineConfigurationResult.CompileResults(IEnumerable1 results) workflowapi_1 | at Automatonymous.StateMachineConnectors.StateMachineConnector1.StateMachineEvents()+MoveNext() workflowapi_1 | at System.Collections.Generic.List1.AddEnumerable(IEnumerable1 enumerable) workflowapi_1 | at System.Linq.Enumerable.ToList[TSource](IEnumerable1 source) workflowapi_1 | at Automatonymous.StateMachineConnectors.StateMachineConnector1..ctor(SagaStateMachine1 stateMachine) workflowapi_1 | --- End of inner exception stack trace --- workflowapi_1 | at Automatonymous.StateMachineConnectors.StateMachineConnector1..ctor(SagaStateMachine1 stateMachine) workflowapi_1 | at Automatonymous.SagaConfigurators.StateMachineSagaConfigurator1..ctor(SagaStateMachine1 stateMachine, ISagaRepository1 repository, ISagaConfigurationObserver observer) workflowapi_1 | at MassTransit.AutomatonymousReceiveEndpointExtensions.StateMachineSaga[TInstance](IReceiveEndpointConfigurator configurator, SagaStateMachine1 stateMachine, ISagaRepository1 repository, Action`1 configure) workflowapi_1 | at Rapid.Workflow.Api.Startup.<>c.b__2_5(IRabbitMqReceiveEndpointConfigurator ep) in /src/Workflow.Api/Startup.cs:line 74

Dependencies are

<PackageReference Include="Automatonymous" Version="4.1.6" />
<PackageReference Include="MassTransit" Version="5.5.5" />
<PackageReference Include="MassTransit.RabbitMQ" Version="5.5.5" />
<PackageReference Include="MassTransit.AspNetCore" Version="5.5.5" />
<PackageReference Include="MassTransit.Automatonymous" Version="5.5.5" /> 
<PackageReference Include="MassTransit.Extensions.DependencyInjection" Version="5.5.5" />
<PackageReference Include="Newtonsoft.Json" Version="12.0.2" />

Thanks for any tips or ideas -

Answer 1

This error seems to crop up because the Saga class had declared some as-yet-unused (but public) events - DOH!

The solution was to remove unused events from the Saga...

// uncomment will fail! public Event<ISatelliteTaskRequest> UnusedEvent { get; private set; }

After looking at this sample https://github.com/selcukusta/masstransit-saga-implementation and cutting my program.cs back to basics - I was still getting the error! So, not a container / IOC / Startup issue.

Next, looking in source for the MassTransit error message (https://github.com/MassTransit/MassTransit/blob/master/src/MassTransit.AutomatonymousIntegration/Configuration/StateMachineConnectors/StateMachineConnector.cs) I realised that the correlating code is possibly reflecting on all public members of the Saga -

So, removing unused events from the Saga class fixes the issue.