How can I check whether a RabbitMQ message queue exists or not?

Question

How can I check whether a message Queue already exists or not?

I have 2 different applications, one creating a queue and the other reading from that queue.

So if I run the Client which reads from the queue first, than it crashes.
So to avoid that i would like to check first whether the queue exists or not.

here is the code snippet of how I read the queue:

QueueingBasicConsumer <ConsumerName> = new QueueingBasicConsumer(<ChannelName>); 
<ChannelName>.BasicConsume("<queuename>", null, <ConsumerName>); 
BasicDeliverEventArgs e = (BasicDeliverEventArgs)<ConsumerName>.Queue.Dequeue();

Solution 1

Don't bother checking.

queue.declare is an idempotent operation. So, if you run it once, twice, N times, the result will still be the same.

If you want to ensure that the queue exists, just declare it before using it. Make sure you declare it with the same durability, exclusivity, auto-deleted-ness every time, otherwise you'll get an exception.

If you actually do need to check if a queue exists (you shouldn't normally need to), do a passive declare of the queue. That operation succeeds if the queue exists, or fails in an error if it doesn't.

Solution 2

This won't work in situations when there is someone else (other application) responsible for q declaration. And I simply could not know all the parameters of the q, just the name.

I would rather use passiveDeclare and check for the IOException that the q does not exists

Solution 3

Currently you can know that info and much more throught RabbitMQ Management HTTP API.

For example, to know if one queue is up at this moment, you can invoke to GET /api/queues/vhost/name interface of the API.

Solution 4

Put below code inside try catch section. If queue or exchange doesn't exist then it will throw error. if exists it will not do anything.

  var channel = connection.CreateModel();


  channel.ExchangeDeclarePassive(sExchangeName);

  QueueDeclareOk ok = channel.QueueDeclarePassive(sQueueName);

   if (ok.MessageCount > 0)
    {
      // Bind the queue to the exchange

     channel.QueueBind(sQueueName, sExchangeName, string.Empty);
    }

Solution 5

Use QueueDeclare() to perform this as suggested. Also, what we have always done, is make the consumer of the queue be the owner of the queue, and always publish to Exchanges which are created and owned by publishers. Consumers then bind their queues to the exchanges that they wish to receive traffic from and use an appropriate route key filter for the traffic they want. In this way, publishers are muted by no consumers for non-durable queues, and consumers are free to come and go with durable or non-durable queues mapped with the appropriate route keys.

This results in an easily administered system and allows web administration to be used to create a durable queue and bind it to an exchange, get some traffic, unbind it, and then inspect the queue contents to understand what traffic and load is coming through the exchange.

View more solutions

Comments

[Jigar Sheth]

Can you please Mention the Syntax for declaring the queue passively in c# api

[scvalex]

Use IModel.QueueDeclare and set passive to true. rabbitmq.com/releases/rabbitmq-dotnet-client/v1.8.1/…

[Oliver]

Really? I just tried using C# QueueDeclare(); and it produced two identical queues on the RabbitMQ dashboard.

[Dalibor Filus]

Queue declaration might be idempotent, but if you don't know the parameters of the queue you are trying to publish to (auto-deleted etc.), queue redeclaration will fail, because of different queue settings.

[WGH]

Checking queue existence might be useful. For example, if you're writing a RPC service, you may want to ensure that RPC client hasn't gone away before processing the message.

[Laurence]

that passive thing from @scvalex doesn't exist anymore in the new versions of rabbitmq c# client. queue.declare is idempotent as long as you pass in the same params (e.g. durable, exclusive, etc)

[Gustavo Andrade Ferreira]

That will only work if the user have configure permissions to the queue. Sometimes you have different users for writing and reading. So i don´t think this is the best solution

[watery]

API links is dead, this may be a more generalized one to the subject.

[Eugene Zakharenko]

You can't tell for everyone that "Don't bother checking." What if I want a single consumer for single query? Just need to check. And your answer doesn't answer the question. I have an active queue declaring and do not want passive, still need to know that the queue exists. Whats then?

[brenthompson2]

I am looking at the split approach of Publishers declaring Exchanges and Consumers declaring Queues and binding them to Exchanges. However, if the Exchange is not declared when the consumer tries to bind the Queue to it, an exception is thrown. Do you ensure that the Publisher is initialized first, are you also declaring the exchanges in the consumer, are you manually creating exchanges the the UI/CLI, or are you doing something else to prevent the issue?

[Majid]

Actually, this is the correct answer. the one that has been chosen as correct, emits a potential risk of declaring and creating abandoned Queues in RabbitMQ server. The QueueDeclarePassive method has been designed to be used in such a situation.

[Caius Jard]

Perhaps this is the working link: rawcdn.githack.com/rabbitmq/rabbitmq-management/v3.8.3/priv/‌​www/…

[Rick O'Shea]

Get a live person to log into the console and maybe give the interested party a phone call or send an email? That's not a serious solution.

[Grwww]

We made the consumer announce it's stuck, and then await for the Exchange to appear (looping on the exception occurring), or for the app to be closed/killed. This allows the system to be started up in any order and for it to be restarted as needed without the publishers or consumers having to be ordered in their startup.