About RabbitMQ Message Services

Overview

The Message Queue architecture allows a designed system to handle large client requests by placing them into a queue to process asynchronously. Message Queues can be placed between an application server and a database server. This setup lets the application server send a response to the requesting user and place the request in the Message Queue. The database server can then pick up the request from the Message Queue and process that transaction.

The Rabbit Message Queue (RabbitMQ) is a messaging system for application-to-application communication. The RabbitMQ module adds the capability to the Decisions Messaging Service, which lets users connect to built-in Flow steps to manage a Rabbit MQ. The RabbitMQ module allows users to queue subscribers so that the Flow can work and push messages to Queues using Flow steps. Users can also integrate with RabbitMQ, take in a message, and then convert the message to any type of data for processing.

Prerequisites

• Active RabbitMQ application
• Installation of the RabbitMQ Module in Decisions. To learn how to install a module, see Installing Modules.
• Setting Up Messaging Overview

Configuration

1. Navigate to Systems > Jobs and Events. Right-click Message Queues and select Add Rabbit Queue.
     
2.  On the Add Rabbit Queue dialog window, enter a Display Name and the Queue Name. Configure any other options necessary and click SAVE.
   

   Configuration Options		Description
   DEFINITION
   	Display Name	Determines how the Queue's name displays.
   	Queue Name	The name of the Queue that the system references.
   	Is Durable Queue	When Decisions create the Queue, this setting keeps the Message permanently. If no one is using the Queue, this setting will reclaim the Message Queue and recreate the Message.
   	Auto Delete	Instructs the Message Server to delete the Queue when its last consumer disconnects.
   	Override Server Info	Allows the specific server to be set up. This includes the Server IP or Name as well as the Port number.
   	Override Virtual Host	Allows the ability to set up multiple virtual hosts allowing the user to host Decisions. The Virtual host runs in order to keep the actual production from interference.
   	Server IP or Name	Specify the IP address or server name
   	Use Default Port	Allows the user to enable using the default port
   	Use SSL	Enables use of SSL
   	Override Queue Credentials	Provides the ability to set up a username and password that can be assigned, allowing specific credentials to be required
   QUEUE ARGUMENTS
   	Queue Type	Specifies the queue type (classic, quorum)
   	Dead Letter Exchange	The queue for undelivered or failed messages
   	Dead Letter Routing Key	Routing key for dead letter
   	Maximum Queue Length	Sets the maximum queue length
   	Message TTL (msec)	Sets the message time-to-live in milliseconds

   
   
3. Navigate to System > Jobs and Events > Message Queues. Right-click on the Message Queue and select Control. Select Test Queue to verify the connection with RabbitMQ. If successful, a dialog popup screen will appear displaying the test result.

   Configuration Options	Description
   Disable Queue	Disables the queue
   Resync Queue	Recreates the Message Queues if necessary and re-synchronizes with the Message Server
   Start Queue	Starts processing Messages on the Message Queues (if stopped)
   Stop Queue	Stops processing Messages on the Message Queues. The Message Server will hold any unprocessed messages.
   Test Queue	Reads the number of awaiting Messages on the Queue and shows a pop-up with the amount of awaiting Messages

   

4. Navigate to System > Jobs and Events > Message Queue Handlers. Click ADD MESSAGE HANDLER.

   Configuration Options		Description
   Handler Name		Name to display in Decisions
   Message Handling		Sets the Message Handling mode to lease the message (lock), lease the message temporarily (lock with auto timeout), remove it after processing (pop), or use it but leave it on the Queue (peek)
   	Lease	Temporarily pulls the message from the queue; The message cannot be pulled while it is leased but will remain in the queue. If the message fails, the lease is removed and made available in the queue. If the message passes, it is removed from the queue. Slightly slower than Get and Remove.
   	Lease w/ Expire	The lease times out, and the message becomes deliverable again in one of two scenarios: the message handler's flow throws an exception.  Decisions sends the message server a NAck (not acknowledged) signal for that message, or the communications channel between Decisions and the message server is broken.
   	Get	Messages will be pulled from the queue but NOT REMOVED, and the Handler Flow will run. It will not check to see if the Handler Flow failed. Due to Get not removing messages, messages will continue to be read repeatedly until something else removes the message.
   	Get and Remove	Messages will be pulled and removed from the queue, and the Handler Flow will run. It will not check to see if the Handler Flow failed. Messages will not be stored in memory if the server shuts down, resulting in data loss. This is quicker than Lease or Lease w/ Expire.
   Active Flow Count		The maximum number of simultaneous Messages that Decisions will process.
   PICK HANDLER FLOW		This Flow is used to process Messages that appear in the Queue.
   Message Queue		The Queue for the Handler to listen to. This is configured in System > Jobs and Events > Message Queues.

   If setting the Message Handler mode to Get or Get and Remove mode, Decisions will auto-ACK every message. If using Lease or Lease w/Expire mode, Decisions will only ACK if the handler's Flow completes successfully. If the Flow throws an exception, Decisions will send a negative ACK (NACK).