Masstransit observer example


  • Has Andrew Cuomo Killed Mass Transit on the Tappan Zee?
  • Dunkirk, Jamestown airports to get infrastructure funding
  • Real-time Chat using MassTransit, RabbitMQ, and SignalR
  • Messaging through a service bus in .NET using MassTransit part 7: intercepting messages
  • What the Delta Variant Means for Return to Office
  • Observer Pattern(C# example):Keeping your objects in the know
  • Has Andrew Cuomo Killed Mass Transit on the Tappan Zee?

    What to do. We held up the Tappan Zee Bridge as a prime example of the conflicts of building in this day and age. On the one hand, Governor Andrew Cuomo deserves a lot of credit for finally kick-starting a project that has been debated for almost a decade as its structural integrity continued to deteriorate.

    Yet to keep the project within the budget parameters he set out, the governor cut mass transit out of the project, a setback for locals already frustrated by congestion on the thoroughfare.

    The Cuomo administration has stressed that the bridge will still be able to add mass transit in the future. As Streetsblog thoughtfully explained yesterday, the odds that will ever be realized is now all but impossible. Streetsblog highlights the fact that in expediting the bridge project, mass transit has been stripped out of the environmental review process. This means a separate environmental review would be required later, instead of being folded in now, adding to the time and expense of adding mass transit in the future, and thus diminishing its realization in the future.

    Yet what is most telling is a historical example Streetsblog dug up: When the George Washington Bridge was first built, designer Othmar Ammann imagined that the entire lower deck would eventually be used for light rail, as Rutgers professor Michael Aaron Rockland tells it in his history of the bridge. By , when the lower deck was actually built, six of the eight lower deck lanes were given to automobiles. The other two were left empty, theoretically for future use by transit.

    It has been said that with the appointment of the doggedly loyal Joe Lhota, the governor is finally at the helm of the M. A Quinnipiac poll yesterday found that two-thirds of New Jersey supports the extension of the 7-Train under the Hudson River.

    But there may only be one person with real sway over the project, and it appears, so far, he just does not care about mass transit.

    Dunkirk, Jamestown airports to get infrastructure funding

    The website created a TicketOpened message and published it to the MassTransit service bus. Then, we built a Windows Service, using the TopShelf library, that subscribed to TicketOpened messages and handled creating the ticket and emailing the customer a confirmation email. But what happens when something goes wrong? Blog posts usually assume the happy path when showing code examples in order to keep them easily digestible. We all know, however, things can and will go wrong.

    If we were persisting to a data store, that could be down, or maybe there was a SQL deadlock. CustomerPortal repository master branch or by building the application in my previous blog post. The final code is in the same repository, but in the error-handling branch. TicketOpenedConsumer class: using Loosely. Contracts; using MassTransit; using System; using System. Diagnostics; namespace Loosely. Message ; if envelope. Contains "poison" throw new Exception "Something bad has happened!

    Message; EmailHelper. Send envelope. What MassTransit does, by default, is retry any message that causes an exception to be thrown in its consumer exactly 4 more times. TicketService class, within your bus initializer code.

    Configuration; using MassTransit; namespace Loosely. SetDefaultRetryLimit 1 ; x. Requeuing Error Messages If you end up with messages in the error queue, you may want to move them back to the primary queue to be processed.

    In RabbitMQ this can be accomplished using the Shovel plugin. Obviously, when we start up our consumer again, it will try 5 times and fail again, moving it back to the error queue. In this case, these messages would end up in the error queue and should probably stay there until the error is corrected.

    It just depends on your business requirements. If, however, the message is mission critical, then the likely scenario would be to fix the bug, redeploy the new code, move the error messages back into the primary queue, and then let them get processed. Transient Failures What about the examples of failures mentioned earlier? A down email or database server?

    A deadlock condition in the SQL Server? These could be considered transient failures — meaning, if we just were to retry later, the message could likely be processed just fine with no modifications to the message or the consumer code. As we saw, MassTransit has a bit of a blunt method to try to account for transient failures… it tries the message 5 times. Perhaps in a deadlock situation, this would work great, but probably not in a network or server outage situation.

    What would be ideal is if we could have the message retry after some timeout delay. Perhaps we could even escalate the delay if subsequent retries fail. For example, try 1 minute later on the first retry, then 5 minutes later on the second retry, and then perhaps fail. However, MassTransit does not. Roll Your Own Retry Delay Logic Assuming this is a pattern you want to implement for a larger application with multiple message types, you will probably want to build the retry delay logic into a common helper class.

    Generic; using System. Diagnostics; using System. Threading; namespace Loosely. TryParse envelope. WriteLine "Message committed. WriteLine "Exception caught. SetHeader "loosely. ToString ; x. SetDeliveryMode MassTransit.

    Replace "server-blip", "server-online blipped " ; throw new Exception "The mail server is down. Replace "server-down", "server-blip downed " ; throw new Exception "The mail server is down.

    Contains "server-disaster" throw new Exception "The mail server is down. Finally, we wrap all of the actual message processing in a try…catch block. Negative one will be our trigger to tell us we need to give up on retrying. If the condition is not met, we re-throw the exception and MassTransit will handle it per normal message processing rules default being to retry 4 more times and then move to the error queue.

    That will put the message back on the bus and our consumer will get called again with it. Good catch. Yes, this can have performance implications. But is this really a problem? In this example, our service is only responsible for processing TicketOpened messages.

    Every TicketOpened message needs to trigger an email to be sent. If the email server is down, then none of the TicketOpened messages are going to be able to successfully be processed. In this case, it probably makes sense for the entire service to slow down and wait until the mail server is back online. If the service were responsible for processing many different types of messages, then this would certainly be an issue.

    However, it begs the question whether it makes sense for a single service to handle different types of messages. In some cases it might, particularly if they all need to be handled in much the same way. But in a lot of cases, it will make more sense to create separate services for your different message types. What happens to the message if the service crashes during the Thread. Caveats and Disclaimers These bloggers, sheesh.

    Bad programmer. Next, with a good suite of tests watching your back, the code in this example could be refactored into shorter methods and perhaps a helper class for the retry delay progression. Finally, the call to Thread. Sleep should probably be refactored into a loop to wake up every couple of seconds to see if the service needs to stop. Other Options Of course there are other ways to build delayed retry logic into your services. The method used in this post is just the simplest to illustrate, but you can take this further.

    For example, take a look at the MassTransit-Quartz project. This uses the open source Quartz. NET scheduler to enable delayed publishing of messages. It does, however, require an ADO. If you need scheduling and visibility into messages that were delayed, then this is your ticket. Another pattern that could be implemented is that of moving the delayed messages to another RabbitMQ queue. Then you could write something that periodically polled that queue and moved the messages back into the primary queue after the desired delay.

    In one case, we might want to spin up multiple. In another case, we may want to have completely different consumers subscribing to the same message type but intending to do different things with the messages. However, my software engineering experience extends back over 25 years. Currently, I am a Developer Educator for Twilio. I guided the company from a print-based newsletter company to an online information services company.

    Real-time Chat using MassTransit, RabbitMQ, and SignalR

    What to do. We held up the Tappan Zee Bridge as a prime example of the conflicts of building in this day and age.

    On the one hand, Governor Andrew Cuomo deserves a lot of credit for finally kick-starting a project that has been debated for almost a decade as its structural integrity continued to deteriorate. Yet to keep the project within the budget parameters he set out, the governor cut mass transit out of the project, a setback for locals already frustrated by congestion on the thoroughfare.

    The Cuomo administration has stressed that the bridge will still be able to add mass transit in the future. As Streetsblog thoughtfully explained yesterday, the odds that will ever be realized is now all but impossible. Streetsblog highlights the fact that in expediting the bridge project, mass transit has been stripped out of the environmental review process.

    The website created a TicketOpened message and published it to the MassTransit service bus. Then, we built a Windows Service, using the TopShelf library, that subscribed to TicketOpened messages and handled creating the ticket and emailing the customer a confirmation email. But what happens when something goes wrong? Blog posts usually assume the happy path when showing code examples in order to keep them easily digestible.

    We all know, however, things can and will go wrong. If we were persisting to a data store, that could be down, or maybe there was a SQL deadlock.

    Messaging through a service bus in .NET using MassTransit part 7: intercepting messages

    CustomerPortal repository master branch or by building the application in my previous blog post. The final code is in the same repository, but in the error-handling branch.

    TicketOpenedConsumer class: using Loosely. Contracts; using MassTransit; using System; using System. Diagnostics; namespace Loosely. Message ; if envelope. Contains "poison" throw new Exception "Something bad has happened! Message; EmailHelper. Send envelope. What MassTransit does, by default, is retry any message that causes an exception to be thrown in its consumer exactly 4 more times. TicketService class, within your bus initializer code.

    Configuration; using MassTransit; namespace Loosely. SetDefaultRetryLimit 1 ; x.

    What the Delta Variant Means for Return to Office

    Requeuing Error Messages If you end up with messages in the error queue, you may want to move them back to the primary queue to be processed. In RabbitMQ this can be accomplished using the Shovel plugin. Obviously, when we start up our consumer again, it will try 5 times and fail again, moving it back to the error queue.

    In this case, these messages would end up in the error queue and should probably stay there until the error is corrected. It just depends on your business requirements. If, however, the message is mission critical, then the likely scenario would be to fix the bug, redeploy the new code, move the error messages back into the primary queue, and then let them get processed.

    Transient Failures What about the examples of failures mentioned earlier? A down email or database server? A deadlock condition in the SQL Server? These could be considered transient failures — meaning, if we just were to retry later, the message could likely be processed just fine with no modifications to the message or the consumer code. As we saw, MassTransit has a bit of a blunt method to try to account for transient failures… it tries the message 5 times.

    Observer Pattern(C# example):Keeping your objects in the know

    Perhaps in a deadlock situation, this would work great, but probably not in a network or server outage situation. What would be ideal is if we could have the message retry after some timeout delay. Perhaps we could even escalate the delay if subsequent retries fail. For example, try 1 minute later on the first retry, then 5 minutes later on the second retry, and then perhaps fail.

    However, MassTransit does not. Roll Your Own Retry Delay Logic Assuming this is a pattern you want to implement for a larger application with multiple message types, you will probably want to build the retry delay logic into a common helper class.

    Generic; using System. Diagnostics; using System. Threading; namespace Loosely. TryParse envelope. WriteLine "Message committed.


    Masstransit observer example