I cannot find anywhere how to manage custom U-type messages. I use MessageCracker and need to understand the corresponding OnMessage method signature. For example my broker sends custom U1,U5, U2 messages, how can I capture those incoming messages inside a OnMessage method? I understand that Tag35 identifies those but if I cannot capture them through OnMessage then MessageCracker becomes kind of useless and I need to identify each message by Tag35 within FromApp or FromAdmin. Any suggestion how to handle those kind of custom U-types?
Thanks
Ah, custom messages. Fun stuff.
You need to add your counterparty's customizations to the DataDictionary xml file. Choose the appropriate FIXnn.xml file for your FIX version.
See here: http://quickfixn.org/tutorial/custom-fields-groups-and-messages
Then, because you are adding custom messages, you'll want to regenerate the QF/n source and rebuild the library so you can get classes for your new messages.
Instructions for rebuilding are here: https://github.com/connamara/quickfixn
You'll need to install Ruby. This annoys some people, but we haven't found any more-windows-oriented code-generator that we don't hate. Sorry in advance.
(If you were just adding fields to existing messages, you could probably get away with not rebuilding. But you're adding messages, so you pretty much have to regenerate/rebuild.)
To Windows developers, it may seem annoying that rebuilding the library is required, but it really is the norm for all the QF engines. FIX is just too fudgey a protocol for a single build to satisfy everyone, because it seems that every counterparty likes to screw with the message definitions.
Related
We are using axon framework version 3.4.2 and found a bug inside our code. The bug relates to a missing event which was not published. The solution is to fix the code but this would not fix the event store and views.
My question is how would one fix this? We thought of appending the events to the event store (we use a JDBC event store), but without the correct data, the new events would not be processed. The best would be to do it in the application by publishing the event in axon and let axon handle all the details, but this is a once-off, correcting action.
Is there any way of "injecting" a once-off event into axon?
The comment which Matt shared is conceptually what you should do.
Thus, to resolve the issue you unintendedly introduced, you should produce a compensation action, aka a command. This command will be handled in your command model, will validate the model's state and publish the desired event.
Added, I am assuming this event of your should originate from an Aggregate, correct?
In Axon terms, that means you want to publish a domain event rather than a regular event.
Although you can publish events on the EventBus or store in the EventStore directly, it is rather complicated to make those domain events through that process.
Thus, as I started off with and what Matt Freeman commented on your question, a compensating action would be the way to go, with or without Axon.
Last note, know that Axon 4.2 is already out for some time now. Although Axon 3 will still under go bug fixes, none of these have occurred in the last year. Simply put, there is no active development on Axon 3. Migrating to a more recent version would thus be beneficial for your project.
I am using Axon 3.1.1 and wanted to know,
How can I get a list of eventprocessor in my configuration file,
I went through the springAmQPmessageSource file but still not sure how to exactly do it.
So that I can pass my event to appropriate eventhandler on Query side.
List<Consumer<List<? extends EventMessage<?>>>> eventProcessors = new CopyOnWriteArrayList<>();
Updated
I was retrieving message from kafka topic and wanted to wire them to specific eventhandler but since I am not able to get evenprocessors, I am not able to do that.
Can you please tell me how to do it, if I am using Axon 3.0.5
If you're using the SpringAmqpMessageSource, you will not need to retrieve the list of eventProcessors you've shared, as Axon will automatically subscribe all the event handling components to it for you.
Subsequently, the events the Message Source receives will automatically be pushed to all the listeners in your query side.
As this is all covered as Axon infrastructure under the hood, there is no one-off way to pull them out of it for your own use (other than potentially wiring them yourself).
Hence, you shouldn't have to do this yourself.
But, maybe I'm missing an obvious point here.
Could you elaborate a little more why you need the list of handlers in the first place?
Can we have a sample of variables available for redefinition of templates, documentation is scarce on this?
In Class package de.codecentric.boot.admin.notify.MailNotifier I read
private static final String DEFAULT_SUBJECT = "#{application.name} (#{application.id}) is #{to.status}";
private static final String DEFAULT_TEXT = "#{application.name} (#{application.id})\nstatus changed from #{from.status} to #{to.status}\n\n#{application.healthUrl}";
In my specific use case I inherited a bunch of applications which I want to ping or monitor they are alive. I have no control on them but my app depends on them.
My app doesn't fail but may misbehave (important point!).
So I added a bunch of customs HealthIndicator to get them monitored by ping, that work perfectly, and I was very pleased by changing an IP a notification was sent, great!
But there is a but, the message sent let me think than the app was failing, while instead the health indicator was status OUT_OF_SERVICE, unnecessary stress for DevOps.
Come to my question, how can I add some extra variables whereby some carefully crafted SPEL will distinguish an Health indicator message status change than an application status change ie webapp going offline.
Is a dictionary of SBA keywords available to use for redefining for example spring.boot.admin.notify.mail.text Mail notifications configuration option?
I guess this is valid to other notifiers being hipchat, Slack.
Thank you.
The context for evaluating the SpEL expression is the event.
Therefore all properties from ClientApplicationEvent (or the corresponding subclass for the event instance (e.g. ClientApplicationStatusChangedEvent)) are available.
If it doesn't suffice you can ship your own subclass of the MailNotifier..
Answer is no, cannot do in current code base without code changes.
SBA notification keywords/variables available are the following:
application.name
application.id
application.healthUrl
application.managementUrl
application.serviceUrl
application.statusInfo.status
from.status
to.status
timestamp
type
We don't have anything else.
However the StatusUpdater.queryStatus looks promising to get some extra data.
I´m just trying to wrap my head around CQRS(/ES). I have not done anything serious with CQRS. Probably I´m just missing something very fundamental right now. Currently, I´m reading "Exploring CQRS and Event Sourcing". There is one sentence that somehow puzzles me in regards to commands:
"A single recipient processes a command."
I´ve seen this also in the CQRS sample application from Greg Young (FakeBus.cs) where an exception is thrown when more then one command handler is registered for any command type.
For me, this is an indication that this is a fundamental principle for CQRS (or Commands?). What is the reason? For me, it is somewhat counter-intuitive.
Imagine I have two components that need to perform some action in response to a command (it doesn´t matter if I have two instances of the same component or two independent components). Then I would need to create a handler that delegates the command to these components.
In my opinion, this is introducing an unnecessary dependency. In terms of CQRS, a command is nothing more than a message that is sent. I don´t get the reason why there should be only one handler for this message.
Can someone tell me what I am missing here? There is probably a very good reason for this that I just don´t see right now.
Regards
I am by no means an expert myself with CQRS, but perhaps I can help shed some light.
"A single recipient processes a command.", What is the reason?
One of the fundamental reasons for this is transactional consistency. A command needs to be handled in one discrete (and isolated) part of the application so that it can be committed in a single transaction. As soon as you start to have multiple handlers, distributing the application beyond a single process (and maintaining transactional consistency) is nearly impossible. So, while you could design that way, it is not recommended.
Hope this helps.
Imagine I have two components that need to perform some action in response to a command (it doesn´t matter if I have two instances of the same component or two independent components). Then I would need to create a handler that delegates the command to these components.
That's the responsibility of events.
A command must be handled by one command handler and must change the state for a single aggregate root. The aggregate root then raises one or more events indicating that something happened. These events can have multiple listeners that perform desired actions.
For example, you have a PurchaseGift command. Your command handler loads the Purchase aggregate root and performs the desired operation raising a GiftPurchased event. You can have one or more listeners to the GiftPurchase event, one for sending an email to the buyer confirming the operation and another to send the gift by mail.
I want to use elements of CQRS pattern in my project. I wonder if i do it right with Command and Events.
The thing that I'm not sure is if event can invoke command. To better show what i want to do I will use diagram and example.
This is an example:
User invoke TripCreateCommand. TripCreateCommandHandler do his job and after success publish TripCreatedEvent.
Now we have two listener to TripCreatedEvent (the order of listener execution does not matter)
First listener (can be execute after the second listener):
for each user in trip.author.friends invoke two Command (the order of commands is important)
PublishTripOnUserWallCommand
SendNewTripEmailNotificationCommand
SendNewTripPlatformNotification
Second listener (can be execute before the first listener):
PublishTripOnUserSocials
And this is sample diagram:
Is this a good way ? Can EventListener invoke Command, or maybe I should do it in some other way ?
Your question is about Mesage Driven Architecture which works together with but otherwise unrelated to CQRS.
Anyway, your diagram is almost correct. The event subscriber/handler (I prefer this terminology) can send new Commands via the service bus, but it's not a rule that you should always do this. I implement quite a lot of functionality directly in the event handler, although probalby would be more clean and reliable to send a new command. It really depends on what I want to do.
Note that the message handlers (commands or events) should not know about other handlers. They should know about the bus and the bus takes care of handling. This means that in your app, the event handlers would take the bus as dependency, create the command and send it via the bus. The event handler itself doesn't know what command handler generated the event and can 'reply' to it.
Usually the commands would be handled independently and you can't guarantee the order (unless they're handled synchronously) so maybe you want the second command to be issued as a result of the first command's handling. Indeed, it can be the case for a Saga.
AFAIK you are talking only about doing things synchronously, so your approach works in this case but it's probably not scalable. Moving to async handling will break this execution flow. However your application can be fine with it, not everyhting needs to be twitter.
A message driven architecture is not that straightforward and for some cases (like you want an immediate response from the backend) it's quite complicated to implement, at least more complicated than with the 'standard' approach. So maybe for those particular cases you might want to do it the 'old' way.
If you're worried about decoupling and testing, you can still design the services as they were message handlers but use them directly, instead of a service bus.
Not sure why you would need Commands for performing the updating the information on the user's wall. Why would you choose not to use a View Model Updater for that task.
Sending an email can be considered a Command but could also easily be viewed as just another View Model update.
Not clear on what the purpose of the SendNewTripPlatformNotification is, so I cannot give any suggestions there...
Some of this could also be a candidate for a Saga. Secondly I'm missing your Domain in the diagram, that is what should be responsible for publishing any events, or do you consider the CommandHandler to be the Domain?