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I'm wondering if it is possible to send a brokered message to a queue/topic where the message is already in a deferred state?

I'm asking this because I currently have a process that does the following ...

  1. The process starts and a brokered message is sent to a queue (this triggers a function that records the message body as an entity in table storage with a 'Processing' status).
  2. Additional work is done in the process
  3. If we get to the end of the process without any issues, another brokered message is sent to the queue with a completion message (this triggers the same function that updates the entity in table storage with a 'Complete' status).

While this method is mostly working, it feels clunky and fragile. I would really like to be able to send a message to the queue and then have the final step make the message visible on the queue so it can be consumed by the function (Durable Function).

I thought about setting the ScheduledEnqueueTimeUtc, but I can't guarantee when the process will finish (I'm thinking worst case scenario here) so I'm not sure how long to set it.

I also looked at the Defer option for a BrokeredMessage but it seems this can only be set from the receiver and not be in a deferred state initially.

Is what I'm trying to do possible with Service Bus brokered messages? Could I set the Scheduled Enqueue time so some ridiculously long time (e.g. 2 hours) and if it reaches that time it is automatically expired and moved to the Dead Letter queue? Should I send the initial message to the Dead Letter queue and then once the process is complete, retrieve it and resubmit it?

Has anyone had any experience with implementing a process like this ... send a start message and only process the message once a completion notification has been received? I need this to be as robust as possible as I'm dealing with financial transactions in this process.

Hopefully my explanation makes sense.

Dazfl
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2 Answers2

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I'm wondering if it is possible to send a brokered message to a queue/topic where the message is already in a deferred state?

That's not possible. You can only delay a brand new message, not defer it. Deferring required a message to be received first for it to have a SequenceNumber.

Using ScheduledEnqueueTimeUtc has its challenges as you will be sending it in the future, but cannot cancel once processing is over. Instead, you could leverage QueueClient.ScheduleMessageAsync() that returns back SequenceNumber immediately. This way you can set the message far into future, but also cancel it if processing is finished earlier.

Sean Feldman
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I ended up solving this issue by keeping the process of sending two messages, but refactoring my durable function to record the messages in Table Storage, check that both messages have been received and if they have, add a new message to Azure Queue Storage. A second function listens to the queue which starts its process.

After much testing, this appears to be quite a robust solution. It then doesn't matter what order the two messages arrive, or how long they take ... as long as both of them have arrive, that is when the second function will kick off.

Dazfl
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