This documentation supports the 21.05 version of Action Request System.
To view an earlier version, select the version from the Product version menu.

Private queues for loopback calls

The AP:Admin-ServerSettings form provides the Private AR Server RPC Socket and Plugin Loopback RPC Socket fields for controlling loopback calls to the AR System server .

A loopback call occurs when the  Approval Server plug-in initiates a call back to the AR System server  while processing approval workflow. During heavy loads, this can cause a server deadlock if enough queues or threads are not available. To avoid this, use a dedicated loopback RPC queue. The valid RPC socket number ranges are:

  • 390621 – 390634
  • 390636 – 390669
  • 390680 – 390694

To use the approval preview feature, you must set either the Private AR Server RPC Socket or the Plugin Loopback RPC Socket.

Private AR Server RPC Socket

The Private AR Server RPC Socket field creates a private queue dedicated to Approval Server  loopback calls only. This setting appears in the AR System server  configuration file with the tag Approval-RPC-Socket.

If both the Private AR Server RPC Socket and Plugin Loopback RPC Socket values are set, Approval Server  uses the Private AR Server RPC Socket.

Plugin Loopback RPC Socket

The Plugin Loopback RPC Socket field creates a private queue for all loopback calls from the plug-in server, regardless of which plug-in application initiates the call. If this value is set and the Private AR Server RPC Socket field is not set, the Plug-in server uses this queue for Approval Server  loopback calls. In other words, Approval Server  shares this queue with other plug-in applications, but not with  AR System users.

This setting appears in the AR System server  configuration file with the label Plugin-Loopback-RPC-Socket.

Note

The Plugin Loopback RPC Socket field of the Server Settings dialog box controls the same setting as the Plugin Loopback RPC Program Number field on the Ports and Queues tab of the AR System Administration: Server Information form.


If the Plugin Loopback RPC Program Number is already defined for the AR System server , enter the same RPC number in the Plugin Loopback RPC Socket field of the Server Settings window. If this queue is not already defined for the server, it will appear in the Server Information dialog box, on the Server Ports and Queues tab, after you enter it in the Server Settings dialog box.

For more information about defining server ports and queues, see Setting ports and RPC numbers.

How Approval Server  uses RPC settings

In releases earlier than Approval Server  7.5.00, RPC settings were used as follows.

Approval Server  used the following RPC program numbers (defined by using fields on the AP:Admin-ServerSettings form):

  • Private AR Server RPC Socket – (Optional) If a value was specified, the Private-RPC-Socket and Approval-RPC-Socket entries were created in the ar.cfg (Windows) or ar.conf (UNIX) file, and a private queue dedicated to  Approval Server  loopback calls was used, instead of using the default administration (admin) queue at 390600.
  • Plugin Loopback RPC Socket – (Optional) If specified, the Plugin-Loopback-RPC-Socket entry was created (or updated) in ar.cfg (or ar.conf), and that queue was used for the Preview feature. If this value was not provided, the Preview feature did not work.

These values were supposed to be different because they were used for different functionalities.

Approval Server  uses the Visualizer sub-plugin to render previews (different from the Preview feature implementation). Therefore, the same RPC queue can be used for approval processing as well as preview generation.

Following this change, the RPC settings are provided by default at the time of installation or upgrade:

  • When performing a fresh installation, the Private-RPC-Socket, Approval-RPC-Socket, and Plugin-Loopback-RPC-Socket entries are created and set to 390680.
  • When upgrading to release 7.5.00 or later:
    • If Private-RPC-Socket, Approval-RPC-Socket, and Plugin-Loopback-RPC-Socket values are already defined in the existing setup, they are not changed.
    • If Approval-RPC-Socket is not defined, but other Private-RPC-Socket entries exist, the Private-RPC-Socket and Approval-RPC-Socket entries are created and set to the next available valid value.
      If this value is not specified, approval processing is done through the default admin queue.
    • If Plugin-Loopback-RPC-Socket is not defined, the corresponding entry is created and set to the same value as that of Approval-RPC-Socket.
      By default, Approval Server  uses this socket to run the Visualizer sub-plugin.

      Warning

      If Plugin-Loopback-RPC-Socket is not defined, Approval Server attempts to use Approval-RPC-Socket to run the Visualizer sub-plugin. Therefore, if Approval-RPC-Socket is missing from ar.cfg (ar.conf), the Preview feature will not work.

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