How can a RabbitMQ Client tell when it loses connection to the server?

I'm guessing that you're using the C# library? (but even so I think the others have a similar event).

You can do the following:

public class MyRabbitConsumer
{
  private IConnection connection;

  public void Connect()
  {
    connection = CreateAndOpenConnection();
    connection.ConnectionShutdown += connection_ConnectionShutdown;
  }

  public IConnection CreateAndOpenConnection() { ... }

  private void connection_ConnectionShutdown(IConnection connection, ShutdownEventArgs reason)
  {

  }
}

This is an example of it, but the marked answer is what lead me to this.

var factory = new ConnectionFactory
{
    HostName = "MY_HOST_NAME",
    UserName = "USERNAME",
    Password = "PASSWORD",
    RequestedHeartbeat = 30
};

using (var connection = factory.CreateConnection())
{
    connection.ConnectionShutdown += (o, e) =>
    {                       
        //handle disconnect                            
    };

    using (var model = connection.CreateModel())
    {
        model.ExchangeDeclare(EXCHANGE_NAME, "topic");
        var queueName = model.QueueDeclare();

        model.QueueBind(queueName, EXCHANGE_NAME, "#"); 

        var consumer = new QueueingBasicConsumer(model);
        model.BasicConsume(queueName, true, consumer);

        while (!stop)
        {
            BasicDeliverEventArgs args;                       
            consumer.Queue.Dequeue(5000, out args);

            if (stop) return;

            if (args == null) continue;
            if (args.Body.Length == 0) continue;

            Task.Factory.StartNew(() =>
            {
                //Do work here on different thread then this one
            }, TaskCreationOptions.PreferFairness);
        }
    }
}

A few things to note about this.

I'm using # for the topic. This grabs everything. Usually you want to limit by a topic.

I'm setting a variable called "stop" to determine when the process should end. You'll notice the loop runs forever until that variable is true.

The Dequeue waits 5 seconds then leaves without getting data if there is no new message. This is to ensure we listen for that stop variable and actually quit at some point. Change the value to your liking.

When a message comes in I spawn the handling code on a new thread. The current thread is being reserved for just listening to the rabbitmq messages and if a handler takes too long to process I don't want it slowing down the other messages. You may or may not need this depending on your implementation. Be careful however writing the code to handle the messages. If it takes a minute to run and your getting messages at sub-second times you will run out of memory or at least into severe performance issues.