In my messaging app I decided to allocate an individual queue for a client. This way routing and security are quite easy. But I can't figure out how to deal with dead-letter queues then (when message expires, let's say). I want to use serverless approach with Azure functions to handle messages from DLQ. It's easy to setup to trigger a function when a message gets placed in a queue. But if I have 1000 clients, that would require 1000 functions?.. From what I can see you can attach a function to a single "trigger" - meaning single queue. Am I missing something here? what's the right approach to uniformly deal with DLQ messages?
Any help is appreciated. Thank you.
If your concern is how to deal with thousands of DLQs, one possible solution would be to configure your queues and set ForwardDeadLetteredMessagesTo property in each of the queue to point to another queue.
That way the dead-lettered messages from all the queues will go in a single queue and you can attach a Function to that queue for processing of such messages.
Ok so i'm relatively new to the servicebus. Working on a project where we use Azure servicebus for queueing messages. Our architecture roughly looks like the following:
So the idea is that in our SourceSystem all kinds of stuff happens, which leads to messages being put on the servicebustopics. Now our responsibility is syncing these events to the external client so they are aware of what we are doing.
Now the issue is that currently we dont use servicebus sessions so message order isnt guaranteed. Also consider the following scenario:
OrderCreated
OrderUpdate 1
OrderUpdate 2
OrderClosed
What happens now is if the externalclients API is down for say OrderUpdate 1 and OrderUpdate 2, we could potentially send the messages in order: OrderCreated, OrderClosed, OrderUpdate 1, OrderUpdate 2.
Currently we just retry a message a few times and then it moves into the deadletter queue for manual reprocessing.
What steps should we take to better guarantee message order? I feel like in the scope of an order, message order needs to be guaranteed.
Should we force the sourcesystem to put all messages for a order in a servicebus session? But how can we handle this with multiple topics? And what do we do if message 1 from a session ends up in the deadletter?
There are a lot of considerations here, should we use a single topic so its easier to manage the sessions? But this opens up other problems with different message structures being in a single topic?
Id love to hear your opinions on this
Have a look at Durable Functions in Azure. You can use the 'Async Http API' or one of the other patterns to achieve the orchestration you need to do.
NServicebus' Sagas might also be a good option, here is an article that does a very good comparison between NServicebus and Durable Functions.
If the external client has to receive all those events and order matters, sending those messages to multiple topics where a topic is per message type will make your mission extremely hard to accomplish. For ordered messaging first you need to use a single entity (queue or topic) with Sessions enabled. That way you can guarantee ordered message processing. In case you have multiple external clients, you'd need to have a session-enabled entity (topic) per external client.
Another option is to implement a pattern known as Process Manager. The process manager would be responsible to make the decisions about the incoming messages and conclude when the work for a given order is completed or not.
There are also libraries (MassTransit, NServiceBus, etc) that can help you. NServiceBus implements Process Manager via a feature called Saga (tutorial) and MassTransit has it as well (documentation).
I don't get it.
Say I have one queve, one topic, one subscroption. And three clients that subscribe on that.
I send a message.
First client recieve a message and call complete() action.
Will second client recieve a message?
What if there will forth client, who subscribe on it?
Question is - when will message completely remove from queve/topic/subscription??
P.S. Case when "one-to-one" - is clear.
I would recommend you check out the Competing Consumers pattern. (https://msdn.microsoft.com/en-us/library/dn568101.aspx?f=255&MSPPError=-2147217396).
You can have many roles (i.e. Azure Worker Role) checking for messages in a queue (competing consumers), locking them exclusively while processing. Each role is fighting for a message, and the first guy who grabs it (by chance), has it "exclusive" for the moment. If the consumer that gets and processes the message succeeds, run the Complete() method, otherwise the Abandon(message). Complete() finishes it for good, and Abandon throws it back into the frenzy of competing consumers. You can even grab it again if you're healthy!
You can set the dead message parameter in the Azure Management Portal which determines how many times it can be reintroduced for other consumers. At some point, things just aren't working, so kill the message so other messages can resume unimpeded.
Let me know if you have more specific needs. Would be happy to help. This pattern works extremely well.
Kindest regards...
I was using AzureQueue to communicate between roles. My messages like "GoToMaintenanceMode", "StopSendingEmails", "DoNotAcceptRequests" etc. But I realized that, it won't work for my scenario when I have multiple instances due to queue message will shows up only 1 instance at a time.
So my question is beside the options below is there an elegant way to handle this issue something like Role.AllInstances.Run() etc.?
the method I'm using it right now:
instance peeks the message, adds it's own instance id to the message and puts it back to the queue, and does not peek the message if it contains it's own instance id.
P.S. I do not want to implement TCP listener, asking for native solution if there is one.
You could use Windows Azure Service Bus Topics/Subscriptions instead of queues. They support multicasting (i.e. multiple receivers).
A short how-to guide can be found here
http://www.windowsazure.com/en-us/develop/net/how-to-guides/service-bus-topics/
Basically, your queue would become a Topic all your instances would become Subscriber to the Topic.
As you do not want TCP listener option or Service bus option. How about extending your same idea with multiple queues. Instance1 will read from Queue1 and Instance2 will read from Queue2 and so on. The only thing you need to handle is the number of queues and simultaneous adding of queue messages to all the queues.
If there are no longer any publishers or subscribers reading nor writing to a Queue, Topic, or Subscription, because of crashes or other abnormal terminations (instance restart, etc.), is that Queue/Topic/Subscription effectively orphaned?
I tested this by creating a few Queues, and then terminating the applications. Those Queues were still on the Service Bus a long time later. It seems that they will just stay there forever. That would be wonderful if we WANTED that behavior, but in this case, we do not.
How can we detect and delete these Queues, Topics, and Subscriptions? They will count towards Azure limits, etc, and we cannot have these orphaned processes every time an instance is restarted/patched/crashes.
If it helps make the question clearer, this is a unique situation in which the Queues/Topics/Subscriptions have special names, or special Filters, and a very limited set of publishers (1) and subscribers (1) for a limited time. This is not a case where we want survivability. These are instance-specific response channels. Whether we use Queues or Subscriptions is immaterial. If the instance is gone, so is the need for that Queue (or Subscription).
This is part of a solution where each web role has a dedicated response channel that it monitors. At any time, this web role may have dozens of requests pending via other messaging channels (Queues/Topics), and it is waiting for the answers on multiple threads. We need the response to come back to the thread that placed the message, so that the web role can respond to the caller. It is no good in this situation to simply have a Subscription based on the machine, because it will be receiving messages for other threads. We need each publishing thread to establish a dedicated response channel, so that the only thing on that channel is the response for that thread.
Even if we use Subscriptions (with some kind of instance-related filter) to do a long-polling receive operation on the Subscription, if the web role instance dies, that Subscription will be orphaned, correct?
This question can be boiled down like so:
If there are no more publishers or subscribers to a Queue/Topic/Subscription, then that service is effectively orphaned. How can those orphans be detected and cleaned up?
In this scenario you are looking for the Queue/Subscriptions to be "dynamic" in nature. They would be created and removed based on use as opposed to the current explicit provisioning model for these entities. Service Bus provides you with the APIs to perform create/delete operations so you can plug these on role OnStart/OnStop events appropriately. If those operations fail for some reason then the orphaned entities will exist. Again you can run clean up operation on them based on some unique identifier for the name of the entities. An example of this can be seen here: http://windowsazurecat.com/2011/08/how-to-simplify-scale-inter-role-communication-using-windows-azure-service-bus/
In the near future we will add more metadata and query capabilities to Queues/Topics/Subscriptions so you can see when they were last accessed and make cleanup decisions.
Service Bus Queues are built using the “brokered messaging” infrastructure designed to integrate applications or application components that may span multiple communication protocols, data contracts, trust domains, and/or network environments. The allows for a mechanism to communicate reliably with durable messaging.
If a client (publisher) sends a message to a service bus queue and then crashes the message will be stored on the Queue until as consumer reads the message off the queue. Also if your consumer dies and restarts it will just poll the queue and pick up any work that is waiting for it (You can scale out and have multiple consumers reading from queue to increase throughput), Service Bus Queues allow you to decouple your applications via durable cloud gateway analogous to MSMQ on-premises (or other queuing technology).
What I'm really trying to say is that you won't get an orphaned queue, you might get poisoned messages that you will need to handled, this blog post gives some very detailed information re: Service Bus Queues and their Capacity and Quotas which might give you a better understanding http://msdn.microsoft.com/en-us/library/windowsazure/hh767287.aspx
Re: Queue Management, you can do this via Visual Studio (1.7 SDK & Tools) or there is an excellent tool called Service Bus Explorer that will make your life easier for queue managagment: http://code.msdn.microsoft.com/windowsazure/Service-Bus-Explorer-f2abca5a
*Note the default maximum number of queues is 10,000 (per service namespace, this can be increased via a support call)
As Abhishek Lai mentioned there is no orphan detecting capability supported.
Orphan detection can be implement externally in multiple ways.
For example, whenever you send/receive a message, update a timestamp in an SQL database to indicate that the queue/tropic/subscription is still active. This timestamp can then be used to determine orphans.
If your process will crash which is very much possible there will be issue with the message delivery within the queue however queue will still be available to process your request. Handling Application Crashes and Unreadable Messages with Windows Azure Service Bus queues are described here:
The Service Bus provides functionality to help you gracefully recover from errors in your application or difficulties processing a message. If a receiver application is unable to process the message for some reason, then it can call the Abandon method on the received message (instead of the Complete method). This will cause the Service Bus to unlock the message within the queue and make it available to be received again, either by the same consuming application or by another consuming application.
In the event that the application crashes after processing the message but before the Complete request is issued, then the message will be redelivered to the application when it restarts. This is often called At Least Once Processing, that is, each message will be processed at least once but in certain situations the same message may be redelivered. If the scenario cannot tolerate duplicate processing, then application developers should add additional logic to their application to handle duplicate message delivery. This is often achieved using the MessageId property of the message, which will remain constant across delivery attempts.
If there are no longer any processes reading nor writing to a queue, because of crashes or other abnormal terminations (instance restart, etc.), is that queue effectively orphaned?
No the queue is in place to allow communication to occur via Brokered Messages, if all your apps die for some reason then the queue still exists and will be there when they become alive again, it's the communication channel for loosely decoupled applications. Regards Billing 'Messages are charged based on the number of messages sent to, or delivered by, the Service Bus during the billing month' you won't be charged if a queue exists but nobody is using it.
I tested this by creating a few queues, and then terminating the
applications. Those queues were still on the machine a long time
later.
The whole point of the queue is to guarantee message delivery of loosely decoupled applications. Think of the queue as an entity or application in its own right with high availability (SLA) as its hosted in Azure, your producer/consumers can die/restart and the queue will be active in Azure. *Note I got a bit confused with your wording re: "still on the machine a long time later", the queue doesn't actually live on your machine, it sits up in Azure in a designated service bus namespace. You can view and managed the queues via the tools I pointed out in the previous answer.
How can we detect and delete these queues, as they will count towards
Azure limits, etc.
As stated above the default maximum number of queues is 10,000 (per service namespace, this can be increased via a support call), queue management can be done via the tools stated in the other answer. You should only be looking to delete queue's when you no longer have producer/consumers looking to write to them (i.e. never again). You can of course create and delete queues in your producer/consumer applications via the namespaceManager.QueueExists, more information here How to Use Service Bus Queues
If it helps make the question clearer, this is a unique situation in which the queues have special names, and a very limited set of publishers (1) and subscribers (1) for a limited time.
It sounds like you need to use Topics & Subscriptions How to Use Service Bus Topics/Subscriptions, this link also has a section on 'How to Delete Topics and Subscriptions' If you have a very limited lifetime then you could handle topic creation/deletion in your app's otherwise you could have have a separate Queue/Topic/Subscription setup/deletion script to handle this logic...