HTTP/HTTPS Messaging in Network Load Balancing Clusters

Updated: June 25, 2007

Applies To: Windows Server 2008

Message Queuing can be implemented in Network Load Balancing clusters to receive and process messages sent to the cluster. To implement Message Queuing in a Network Load Balancing cluster, enable the same Message Queuing features on all nodes in a cluster. For example, if you install Message Queuing with HTTP support on one node, install Message Queuing with the same functionality on all other nodes.

All computers in the cluster are addressed by the same virtual cluster IP address or set of virtual cluster IP addresses, and when messages are sent over HTTP transport to a queue at a cluster IP address, a TCP session is established with one of the hosts in the cluster. Messages can be sent only to destinations specified by direct format names that include a URL or IP address of the cluster.

In a Web farm implementation, such as a Network Load Balancing cluster, successive HTTP connections from the same source might be directed to two different servers. This means that end-to-end reliable messaging is difficult, and Message Queuing does not guarantee exactly-once delivery through a Web farm, although a best-effort attempt is made by means of a lightweight nonpersistent duplicate removal mechanism. This issue can be addressed by the use of Message Queuing's store and forward feature. Store and forward mapping uses XML files located on Message Queuing computers, with Message Queuing usually installed on each host in the Network Load Balancing cluster. These XML files maintain a mapping between the logical external URL or IP address to which the message is sent, and the physical internal address of a queue. For every incoming message arriving at a Network Load Balancing host running Message Queuing with store and forward functionality, the Message Queuing service will read the logical address to which it was sent. If a message meets mapping criteria, it is forwarded further into the enterprise. For more information, see HTTP Message Redirection.

Similar Web farms and store and forward functionality can also be implemented using DNS round-robin distribution, and network address translation (NAT). For an overview of these, see High Availability for Message Queuing.

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