In MassTransit Send and RequestClient will be mapped to exchange or queue, That will be handled by LoadBalanced Consumer.
But for Publish Message, It will be consumed by all the instances that are running and waiting for the Message.
So, In StateMachine, Consumer has to publish the Events, That will make if more than once StateMachine Instance running it will be Picked by both StateMachine and Process will be duplicated? This is what happening at my work. So, We end up running Single StateMachine Instance.
await context.Publish(new
{
context.Message.OrderId,
context.Message.Timestamp,
context.Message.CustomerNumber,
context.Message.PaymentCardNumber,
context.Message.Notes
});
This publishes the events to Saga, if Saga is running in LoadBalancer. Both Instance will be receiving the SameEvent. And Start Processing the Event and changing the Next State.
If this is the Case, How to solve this. Only one StateMachine Should Pick the published message at once.
We end up running Single StateMachine Instance. So, the Published message wont be picked by both instance and will endup haivng duplicate process.
The Current Implmentation:
Have a REST Api - That receives the request to Start the Initial State.
var sendToUri =
new Uri(
$"rabbitMq://{_rabbitMqConfig.Host}/{_rabbitMqConfig.VirtualHost}-{_rabbitMqConfig.WfSagaQueue}");
var endPoint = await bus.GetSendEndpoint(sendToUri);
var req = wfRequest;
await endPoint.Send<IWfExecRequest>(req);
In the StateMachine :
services.AddMassTransit(x =>
{
x.AddConsumer<WfExecRequestConsumer>();
x.AddConsumer<WfTaskCompletedConsumer>();
x.UsingRabbitMq((context, cfg) =>
{
var wfTaskExecHandler = context.GetRequiredService<IWfTaskExecHandler>();
var wfManagementClient = context.GetRequiredService<IWfManagementClient>();
var wfSagaStateMachine = new MsrAutomationStateMachine(wfTaskExecHandler, wfManagementClient);
cfg.Host(HostCredets);
cfg.ReceiveEndpoint(queueName: "msr-automation-wf-exec-request", configureEndpoint: e =>
{
e.PrefetchCount = 1;
e.ConfigureConsumer<WfExecRequestConsumer>(context);
e.StateMachineSaga(wfSagaStateMachine, repo);
});
cfg.ReceiveEndpoint(queueName: "WfTaskCompleted", configureEndpoint: e =>
{
e.PrefetchCount = 1;
e.ConfigureConsumer<WfTaskCompletedConsumer>(context);
});
});
});
This StateMachine Receives , WfExecRequest (Inital Event), TaskCompleted and TaskFaulted (From Muliple Consumer Saga/Consumer) - This was done at Consumer Side as Context.Publish.
So, What I see if we Run more than one Instance of the same StateMachine the TaskCompled Message getting Consumed by both Instances.
Thanks Again.
First, clearly something is wrong with your configuration. If the saga state machine is running on a single queue (receive endpoint, regardless of how many instances of your service are running) it will automatically load balance on that single queue across all running instances.
If you are running multiple instances of the saga state machine on different queues, well yeah, you're basically doing it wrong.
Second, I'm not sure what "LoadBalancer" is but typically something that unnecessary when using a message broker. If "LoadBalancer" is something for your HTTP/API endpoints, that's fine, but the broker and the queue are the scale out points in a message-based system.
If you had posted actual code, or shared some explicit details that would help as it is now it's entirely based on supposition.
Related
How to connect an endpoint(exchange-exchange-queue) in masstransit, accumulate data in the queue, and then, after some time, connect a consumer to this endpoint?
I wanted to do something like:
Task.Run(async () =>
{
for (var i = 0;; i++)
{
await _bus.Publish(new Event(i), stoppingToken);
await Task.Delay(1_000, stoppingToken);
}
});
// a command comes to connect the consumer
var endpoint = _bus.ConnectReceiveEndpoint();
await endpoint.Ready;
// I prepare the consumer, as soon as it is ready, I connect it,
then I read the data that has accumulated during the preparation
(my consumer needs to load the state before reading the data,
and also cannot skip the data during its preparation)
endpoint.ReceiveEndpoint.ConnectConsumer(() =>
_serviceProvider.GetRequiredService<EventConsumer>());
but this code will not create an exchange-exchange relationship, so the queue will be empty
If the exchange bindings (wired to the receive endpoint, which ultimately is a queue) do not exist when messages are published, they are discarded by RabbitMQ.
You would need to connect the receive endpoint in advance, so that the messages end up in the queue.
I'm running a MassTransit configuration with AmazonSQS. In my program I start by creating a receiveenpoint with the queue "input-queue1", I subscribe this SQS queue to an SNS topic named "topic1" and associate a consumer to this receiveendpoint that does some standard printing of the messages it receives. After starting the bus i want to subscribe the already created queue "input-queue1" to another SNS topic, named "topic2", but I couldn't find a way of doing this after starting the Bus (It's important to me that i can do this after the Bus is started). Is there a way of doing this and i'm just missing something, or is it not possible at all? (I tried with the commented portion of the code but it didn't work)
class Program
{
static async Task Main(string[] args)
{
var bus = Bus.Factory.CreateUsingAmazonSqs(x =>
{
x.Host(Constants.Region, h =>
{
h.AccessKey(Constants.AccesskeyId);
h.SecretKey(Constants.SecretAccessKey);
});
x.ReceiveEndpoint("input-queue1", e =>
{
e.Subscribe("topic1", callback => { });
e.Consumer(() => new Handler());
});
});
bus.StartAsync().Wait();
/*var handle = bus.ConnectReceiveEndpoint("input-queue1", e => {
e.Subscribe("topic2", callback => { });
});
var ready = await handle.Ready;*/
Console.WriteLine("Listening to messages...");
Console.WriteLine("Press enter to quit");
Console.ReadLine();
}
}
You can't change the topology of a receive endpoint once it has been created. This means that no new topic subscriptions can be created, and existing subscriptions cannot be removed.
If you need to change the configuration of the receive endpoint, you would need to do it yourself by using the SNS API to add the subscription yourself. I would question why you would want to do this though. If the consumer isn't able to consume the message forwarded to the queue, it would be moved to the skipped queue.
When a subscriber of a topic throws an exception non-handled message lands in {subscribername}_error queue.
Given the example:
const string subsriberName = "AnotherSubscriber";
cfg.SubscriptionEndpoint<AnotherThingHappened>(host, subsriberName, configurator =>
{
configurator.Handler<AnotherThingHappened>(context =>
{
Console.WriteLine(context.Message.AnotherThingType);
if (Random.NextDouble() < 0.1)
{
throw new Exception("Oups, I failed :(");
}
return Task.CompletedTask;
});
});
It created "AnotherSubscriber" subscription on topic ObjectCreatedA. But when it fails the message goes to the queue anothersubscriber_error. It makes it harder to diagnose, monitor and replay messages. Because from ASB perspective this is just an ordinary queue.
How do I route failures to the DLQ of topic ObjectCratedA/AnotherSubscriber instead of **_error one?
Thanks in advance.
This is now possible as of MassTransit 6.2, see the related GitHub issue.
Your configuration will now need to look something like:
cfg.SubscriptionEndpoint(
"my-subscription",
"my-topic",
e =>
{
e.ConfigureConsumer<MyConsumer>(provider);
// Send failures to built-in Azure Service Bus Dead Letter queue
e.ConfigureDeadLetterQueueDeadLetterTransport();
e.ConfigureDeadLetterQueueErrorTransport();
});
I've been trying to come up with a demo of a website that uses MassTransit with RabbitMQ to post messages to a service running on Service Fabric as a Stateful service.
Everything was going fine, my client would post a message:
IBusControl bus = BusConfigurator.ConfigureBus();
Uri sendToUri = new Uri($"{RabbitMqConstants.RabbitMqUri}" + $"{RabbitMqConstants.PeopleServiceQueue}");
ISendEndpoint endPoint = await bus.GetSendEndpoint(sendToUri);
await endPoint.Send<ICompanyRequest>(new {CompanyId = id });
My consumer in my service fabric service was defined like:
IBusControl busControl = Bus.Factory.CreateUsingRabbitMq(cfg =>
{
IRabbitMqHost host = cfg.Host(new Uri(RabbitMqConstants.RabbitMqUri), h =>
{
h.Username(RabbitMqConstants.UserName);
h.Password(RabbitMqConstants.Password);
});
cfg.ReceiveEndpoint(host, RabbitMqConstants.PeopleServiceQueue, e =>
{
e.Consumer<PersonInformationConsumer>();
});
});
busControl.Start();
This does allow me to consume the message in my class and I can process it fine. The problem comes when we want to use IReliableDictonary or IReliableQueue or anything that needs to reference the context that is run from the RunAsync function in the service fabric service.
So my question is, how can I configure (is it possible) MassTransit to work within a Stateful Service Fabric Service which knowledge of the service context itself?
Many thanks in advance.
Mike
Update
Ok, I've made some progress on this, if I point the register routines to my message consumer class (eg):
ServiceRuntime.RegisterServiceAsync("ServiceType", context => new PersonInformationConsumer(context)).GetAwaiter().GetResult();
ServiceEventSource.Current.ServiceTypeRegistered(Process.GetCurrentProcess().Id, typeof(PersonInformationConsumer).Name);
Then in my consumer class for my messages I can do the following:
internal sealed class PersonInformationConsumer : StatefulService, IConsumer<ICompanyRequest>
{
private static StatefulServiceContext _currentContext;
#region Constructors
public PersonInformationConsumer(StatefulServiceContext serviceContext) : base(serviceContext)
{
_currentContext = serviceContext;
}
public PersonInformationConsumer() : base(_currentContext)
{
}
I can now successfully call the service message:
ServiceEventSource.Current.ServiceMessage(this.Context, "Message has been consumed, request Id: {0}", context.Message.CompanyId);
The problem I have now is trying to store something on the IReliableDictionary, doing this causes as "Object reference not set to an instance of an object" error :( ... any ideas would be appreciated (although may not read until new year now!)
public async Task Consume(ConsumeContext<ICompanyRequest> context)
{
ServiceEventSource.Current.ServiceMessage(this.Context, "Message has been consumed, request Id: {0}", context.Message.CompanyId);
using (ITransaction tx = StateManager.CreateTransaction())
{
try
{
var myDictionary = await StateManager.GetOrAddAsync<IReliableDictionary<string, long>>("myDictionary");
This is causing the error.... HELP! :)
You'll need to do a bit more to get MassTransit and stateful services working together, there's a few issues to concern yourself here.
Only the master within a stateful partition (n masters within n partitions) will be able to write/update to the stateful service, all replicas will throw exceptions when trying to write back any state. So you'll need to deal with this issue, on the surface it sounds easy until you take in to consideration the master can move around the cluster due to re-balancing the cluster, the default for general service fabric applications is to just turn off the processing on the replicas and only run the work on the master. This is all done by the RunAsync method (try it out, run 3 stateful services with something noddy in the RunAsync method, then terminate the master).
There is also partitioning of your data to consider, due to stateful services scale with partitions, you'll need to create a way to distributing data to separate endpoint on your service bus, maybe have a separate queue that only listens to a given partition range? Say you have a UserCreated message, you might split this on country UK goes to partition 1, US goes to partition 2 etc...
If you just want to get something basic up and running, I'd limit it to one partition and just try putting your bus creation within the the RunAsync and shutdown the bus once a cancelation is requested on the cancelation token.
protected override async Task RunAsync(CancellationToken cancellationToken)
{
var busControl = Bus.Factory.CreateUsingRabbitMq(cfg =>
{
IRabbitMqHost host = cfg.Host(new Uri(RabbitMqConstants.RabbitMqUri), h =>
{
h.Username(RabbitMqConstants.UserName);
h.Password(RabbitMqConstants.Password);
});
cfg.ReceiveEndpoint(host, RabbitMqConstants.PeopleServiceQueue, e =>
{
// Pass in the stateful service context
e.Consumer(c => new PersonInformationConsumer(Context));
});
});
busControl.Start();
while (true)
{
if(cancellationToken.CancellationRequested)
{
//Service Fabric wants us to stop
busControl.Stop();
cancellationToken.ThrowIfCancellationRequested();
}
await Task.Delay(TimeSpan.FromSeconds(1));
}
}
I have a saga setup in a fork/join configuration.
Events defined on the saga
FileMetadataMsg
FileReadyMsg
SomeOtherMsg
Process starts off when a file comes in on a separate listener.
Publishes SagaStart(correlationId)
Publishes FileSavedToMsg(correlationId, fileLoc)
Publishes FileMetadataMsg(correlationId, metadata)
Publishes FileReadyMsg(correlationId, fileLoc)
Downstream endpoint of does some work on the file
Consumer<FileSavedToMsg>
Publishes SomeOtherMsg(GotTheFileMsg.correlationId, data)
I am getting a FileSavedToMsg in the saga_skipped queue. I can only assume it's due to having a correlationId on the FileSavedToMsg because the saga itself is not using FileSavedToMsg in its state machine and does not have an Event<FileSavedToMsg>.
If this is the reason why...should I be passing the correlationId along in a field other than the CorrelationId, so the saga doesn't see it? I need it somewhere so I can tag SomeOtherMsg with it.
Here is how the saga endpoint is defined
return Bus.Factory.CreateUsingRabbitMq(cfg =>
{
var host = cfg.Host(new Uri("rabbitmq://localhost/"), h =>
{
h.Username("guest");
h.Password("guest");
});
cfg.ReceiveEndpoint(host, "study_saga", epCfg =>
{
epCfg.StateMachineSaga(machine, repository);
});
});
Here is how the worker endpoint is defined
return Bus.Factory.CreateUsingRabbitMq(x =>
{
var host = x.Host(new Uri("rabbitmq://localhost/"), h =>
{
h.Username("guest");
h.Password("guest");
});
x.ReceiveEndpoint(host, "study_3d_volume_worker", c =>
{
c.PrefetchCount = 1;
c.Instance(_studyCreatedMsgConsumer);
});
});
These are running on the same machine, but in seperate Console/Topshelf applications.
If you are getting messages on a queue that are not consumed by a consumer on that receive endpoint, it might be that you either previously were consuming that message type and removed it from the consumer (or saga, in your case) or you were using the queue from some other purpose and it consumed that message type.
Either way, if you go into the RabbitMQ management console and look for the queue, you can expand the Bindings chevron, click to go to the exchange of the same name (that's a standard MassTransit convention), and then expand the bindings of the exchange to see which message types (the exchanges named like .NET type names) are bound to that exchange.
If you see one that is not consumed by the endpoint, that's the culprit. You can Unbind it using the UI, after which messages published will no longer be sent to the queue.