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();

Gudrin

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(); – Gudrin

I have added that code snippet to your post. In the future, please click the edit link when adding more context, instead of adding a comment. For more information, see the section When Should I Comment? on the Help page for Comments. – Relic

Answer 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.

Fosque

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

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

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

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. – Adriell

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. – Cupid

that passive thing from @Fosque 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) – Laquitalar

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 – Divot

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? – Sphincter

Answer 2

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);
    }

Walworth

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. – Tombola

Thank you +1. One point worth noting is to keep channel only for this checking, because if the check fails, channel becomes useless. See: github.com/streadway/amqp/issues/167 . Unrelated note: channel is IDisposable. – Wishful

Answer 3

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

Wilderness

Answer 4

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.

Ellipticity

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

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

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. – Semitrailer

Answer 5

There is a meta api in spring-amqp(java implementation)

@Autowired
public RabbitAdmin rabbitAdmin;

//###############get you queue details##############
Properties properties = rabbitAdmin.getQueueProperties(queueName);

//do your custom logic
if( properties == null)
{
    createQueue(queueName);
}

Dodecagon

Answer 6

As mentioned in other answers, channel.QueueDeclarePassive(QueueName) will allow you to check queue's existence without attempting to redeclare (e.g. if you changed the queue settings and would otherwise cause an exception).

However, QueueDeclarePassive() seems to only check the root vhost. You may (haven't tested) get a false negative if your target queue is actually in a custom vhost. You will (tested) get a false positive, if a queue with the same name exists in root vhost.

Maybe wrapping QueueDeclare() in try-catch could be a better way to go, though IMO the RabbitMQ.Client.Exceptions.OperationInterruptedException you'll get is too catch-all for it to be a safe approach.

Ineludible

Answer 7

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.

Antechamber

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? – Febrifuge

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. – Antechamber

Answer 8

In my humble opinion, best way is to override rabbitmq default configuration.

Main class should disable default rabbit configuration:

    @SpringBootApplication
    @EnableAutoConfiguration(exclude 
  {org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration.class})
  public class MyApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

}

my rabbitmq properties are in rabbitmq.properties file:

...
    rabbitmq.queue=my-queue
...

Then just create own configuration rabbitmq component:

@Component
@EnableRabbit
@PropertySource("classpath:rabbitmq.properties")
public class RabbitMQConfiguration
{
...
    @Value("${rabbitmq.queue}")
    private String queueName;

...

    @Bean
    public Queue queue() {
        return new Queue(queueName, false);
    }
...

Also consumer should be setuped:

@Component
@PropertySource("classpath:rabbitmq.properties")
public class MyConsumer
{
    private static Logger LOG = LogManager.getLogger(MyConsumer.class.toString());

    @RabbitListener(queues = {"${rabbitmq.queue}"})
    public void receive(@Payload Object data) {
        LOG.info("Message: " + data) ;
    }

Now when client starts it would automatically create queue if it does not exists. If queue exists it do nothing.

Outwash