Rerouting with queue manager aliases

Fail-over is a common situation that illustrates the important part that Queue Manager Aliases play in routing.

In the following examples, you can see a client communicating with a server, and a have a backup server that can be used if the main server fails, or is taken down for maintenance:

Figure 1. Queue manager aliases and fail-over.

The diagram above shows the local client queue manager, with a connection to ServerQM and a remote queue definition for TargetQueue@ServerQM. The server (bottom left) has a local queue as the target for the example message, and this is mimicked by the backup server (bottom right). Additionally, on the client queue manager, there is a Queue Manager Alias mapping the name Server to ServerQM. This mapping is then used for messages put to the server. The message resolution is shown below for the normal operating configuration, where a message put to TargetQueue@Server is directed to TargetQueue@ServerQM:

Figure 2. Routing traffic using a "server" alias

The alias maps messages for Server to ServerQM, and this selects the remote queue definition TargetQueue@ServerQM. If the network administrator needs to route traffic to the backup server, only the Queue Manager Alias needs to be changed (it is in fact deleted, and recreated with a different target name, in this case BackupQM):

Figure 3. Routing traffic to the backup server, using a "server" alias

The change of alias reroutes the message to a different remote queue, and hence on to the backup queue manager and to TargetQueue@BackupQM. There is a pair of message routes, one to each server, and a Queue Manager Alias to choose between the message routes, as shown in the following diagram:

Figure 4. Choosing between message routes

The example above required a change to every client on a system that requires rerouting to a backup server. If there are a large number of clients this might be impractical. In addition, each client requires two complete message route definitions (a remote queue and a connection definition for each). You can avoid the need to change the client by having a second server ready to listen on the same address and port as the first. When the administrator wants to change over the first can be brought down, and the second can change over. In this situation it might be useful to keep the names of the servers different. The backup server can be given a Queue Manager Alias mapping BackupQM to ServerQM. This allows BackupQM to take the place of ServerQM.


Terms of use | WebSphere software

(c) Copyright IBM Corporation 2004, 2005. All rights reserved.