service-bus-ruby-how-to-use-queues.md

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How to use Azure Service Bus queues with Ruby | Microsoft Docs	Learn how to use Service Bus queues in Azure. Code samples written in Ruby.	service-bus-messaging	ruby	sethmanheim	timlt		0a11eab2-823f-4cc7-842b-fbbe0f953751	service-bus-messaging	na	na	ruby	article	08/10/2017	sethm

How to use Service Bus queues with Ruby

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This guide describes how to use Service Bus queues. The samples are written in Ruby and use the Azure gem. The scenarios covered include creating queues, sending and receiving messages, and deleting queues. For more information about Service Bus queues, see the Next Steps section.

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[!INCLUDE service-bus-ruby-setup]

How to create a queue

The Azure::ServiceBusService object enables you to work with queues. To create a queue, use the create_queue() method. The following example creates a queue or prints out any errors.

azure_service_bus_service = Azure::ServiceBus::ServiceBusService.new(sb_host, { signer: signer})
begin
  queue = azure_service_bus_service.create_queue("test-queue")
rescue
  puts $!
end

You can also pass a Azure::ServiceBus::Queue object with additional options, which enables you to override the default queue settings, such as message time to live or maximum queue size. The following example shows how to set the maximum queue size to 5 GB and time to live to 1 minute:

queue = Azure::ServiceBus::Queue.new("test-queue")
queue.max_size_in_megabytes = 5120
queue.default_message_time_to_live = "PT1M"

queue = azure_service_bus_service.create_queue(queue)

How to send messages to a queue

To send a message to a Service Bus queue, your application calls the send_queue_message() method on the Azure::ServiceBusService object. Messages sent to (and received from) Service Bus queues are Azure::ServiceBus::BrokeredMessage objects, and have a set of standard properties (such as label and time_to_live), a dictionary that is used to hold custom application-specific properties, and a body of arbitrary application data. An application can set the body of the message by passing a string value as the message and any required standard properties are populated with default values.

The following example demonstrates how to send a test message to the queue named test-queue using send_queue_message():

message = Azure::ServiceBus::BrokeredMessage.new("test queue message")
message.correlation_id = "test-correlation-id"
azure_service_bus_service.send_queue_message("test-queue", message)

Service Bus queues support a maximum message size of 256 KB in the Standard tier and 1 MB in the Premium tier. The header, which includes the standard and custom application properties, can have a maximum size of 64 KB. There is no limit on the number of messages held in a queue but there is a cap on the total size of the messages held by a queue. This queue size is defined at creation time, with an upper limit of 5 GB.

How to receive messages from a queue

Messages are received from a queue using the receive_queue_message() method on the Azure::ServiceBusService object. By default, messages are read and locked without being deleted from the queue. However, you can delete messages from the queue as they are read by setting the :peek_lock option to false.

The default behavior makes the reading and deleting a two-stage operation, which also makes it possible to support applications that cannot tolerate missing messages. When Service Bus receives a request, it finds the next message to be consumed, locks it to prevent other consumers receiving it, and then returns it to the application. After the application finishes processing the message (or stores it reliably for future processing), it completes the second stage of the receive process by calling delete_queue_message() method and providing the message to be deleted as a parameter. The delete_queue_message() method will mark the message as being consumed and remove it from the queue.

If the :peek_lock parameter is set to false, reading and deleting the message becomes the simplest model, and works best for scenarios in which an application can tolerate not processing a message in the event of a failure. To understand this, consider a scenario in which the consumer issues the receive request and then crashes before processing it. Because Service Bus has marked the message as being consumed, when the application restarts and begins consuming messages again, it will have missed the message that was consumed prior to the crash.

The following example demonstrates how to receive and process messages using receive_queue_message(). The example first receives and deletes a message by using :peek_lock set to false, then it receives another message and then deletes the message using delete_queue_message():

message = azure_service_bus_service.receive_queue_message("test-queue",
  { :peek_lock => false })
message = azure_service_bus_service.receive_queue_message("test-queue")
azure_service_bus_service.delete_queue_message(message)

How to handle application crashes and unreadable messages

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 unlock_queue_message() method on the Azure::ServiceBusService object. This call causes 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.

There is also a timeout associated with a message locked within the queue, and if the application fails to process the message before the lock timeout expires (for example, if the application crashes), then Service Bus unlocks the message automatically and makes it available to be received again.

In the event that the application crashes after processing the message but before the delete_queue_message() method is called, then the message is redelivered to the application when it restarts. This process is often called At Least Once Processing; that is, each message is 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 message_id property of the message, which remains constant across delivery attempts.

Next steps

Now that you've learned the basics of Service Bus queues, follow these links to learn more.

• Overview of queues, topics, and subscriptions.
• Visit the Azure SDK for Ruby repository on GitHub.

For a comparison between the Azure Service Bus queues discussed in this article and Azure Queues discussed in the How to use Queue storage from Ruby article, see Azure Queues and Azure Service Bus Queues - Compared and Contrasted