I have a nServicebus application,now my application reads messages from handler and remove the messages from bus automatically. But what I want is that after retriving messages from Handler it should not remove messages from bus.And after my message processing which is done by my code, I will remove the message from bus. It means I have to control the messages.
Thank in advance
Susanta Samanta
NServiceBus runs all handlers in a TransactionScope, that means that if your code throws an exception the message will be put back in the queue and retried later. So you shouldn't worry about catching any exceptions/managing how messages get removed from the queue, NSB takes care of that for you.
If you can provide some more info on what you're trying to do I might be able to help you some more?
Related
Currently I have an IErrorHandler implementation dealing with messages going to the Rebus error queue. That handler then publishes messages to a saga that throttles output to a Slack notification channel. I think there may be an easier way to do this though. I would like to have the saga implement an IHandleMessages against messages from the Rebus error queue itself. Is that possible? Currently, we have the FleetManager process enabled and for my custom IErrorHandler to work it has to dual publish errors both to the error queue and to FleetManager using the FleetManager API options. This allows my IErrorHandler to be called so I can publish a custom message to start the slack saga and also feeds FleetManager with the data it needs. The problem with my approach is that the Rebus error queue just grows with data I no longer care about. So I guess my question is: is there a way to handle those Rebus error queue messages? Or perhaps even better, is there a simple way to make those error queue messages go away once I know I have them in my saga?
Note: the reason for the saga and to not simply use a FleetManager Slack web hook is to notify based on custom count thresholds of errors, rather than for every error encountered.
I think I just realized one approach I could take, which is to still use my custom IErrorHandler, yet not actually handle the poison message so that it never makes it to the error queue regardless. Instead I would just publish my custom message that is handled by the saga.
I am using RabbitMQ version 3.0.2 & I see close to 1000 message in Error queue. I want to know
At what point messages are moved to the error queues?
Is there a way to know why a certain message is being moved to an error queue?
Is there any way to move message from error queue to normal queue?
Thank you
a) they fail to deserialize or b) the consumer throws an exception processing that message five times
Not really... If you peek at the message in the queue, the payload headers might contain a note but I don't think we did that. If you turn logging on (NLog, log4net, etc) you should be able to see the exceptions in your log. You'll have to correlate message ids at that point to figure out exactly why.
There is no built in way via MassTransit. Mostly because there doesn't seem to be a great, generic way to handle this. Everyone wants some process around this. Dru did create a BusDriver app (in the main MT source repo) that could be used to move messages back to the exchange in question. This default behaviour is there so you at least know things have been failing if you don't put in the infrastructure to handle it.
To add to Travis' answer, During my development I found some other reasons for messages going onto the error queue:
The published message type has no consumer
A SAGA and a consumer are expecting the same concrete message type. Even if you try and differentiate using "Accepts" and ".Selected", both a SAGA and a Consumer should not be programmed to receive the same message type.
If I queue up a bunch of tasks into ServiceStack MQ, they are picked up by registered handlers for processing as expected. However if my handler application exits during processing or crashes, the message seems to be gone for ever.
I see that it does support retries, and a dead letter queue, but are messages only retried if they explicitly throw and exception from the handler?
Is there any way to have the framework handle keeping the message around until a success result is returned from the handler?
I am wondering what would be the best practice when a consumer is not able to handle the message it receives. What would be the mechanism to notify the rabbit to it will either put it back on to the queue or move to an error queue?
im using the .net client from rabbitmq
Either discard it or put it on an error queue. If there is a problem with the message such that the consumer cannot handle it then do not put it back on the queue as the consumer will just try to read it again.
It is an exception so handle it as such. In the exception handling you should raise an error message stating what happened and what you have done with the message. Best practice is to put it on an error queue where it could be handled manually.
I have a situation where the Maxtries in my MSMQ is 5. After 5 times nservicebus sends the message to the Error que that I have defined. Now I want to perfomr some further action when this happens (I have to update status of some processes to Error)
Is it possible to write a handler in my Saga class to read these error queues?
Thanks in Advance
Haris
If your are using 2.x you may want to consider writing a separate endpoint where the error queue is its input queue. The downside to this is that the messages will come off the queue. Assuming you still want to store them, you'll have to push them off to a database or some other type of storage.
You could also write a Saga that polls the error queue to check for messages and updates the appropriate status. After each time you check the queue, you would need to request another Timeout.
In 3.0, you have more control over the exceptions, and can implement your own way to handle the errors. If you implement the interface IManageMessageFailures, you can do your work there.
As an alternative to the solutions provided by Adam, you can subscribe to events raised by ServiceControl which are raisesd when a messages is sent to the errorqueue. See the official documentation about this here: http://docs.particular.net/servicecontrol/contracts
Another approach would be the notification API as described here: http://docs.particular.net/nservicebus/errors/subscribing-to-error-notifications. It allows you to subscribe to certain events (not event messages) like "MessageSentToErrorQueue" directly on the endpoint, so you wouldn't need to consume the error queue.