Persistent and Replicated Message Queue

VCS includes a sophisticated mechanism for maintaining event messages that ensures messages are not lost. On each node, VCS queues messages to be sent to the notifier process. This queue is guaranteed persistent as long as VCS is running and the contents of this queue remain the same on each node. Therefore, if the group with notifier configured as a resource fails on one of the nodes, notifier is failed over to another node in the cluster. Because the message queue is guaranteed to be consistent and replicated across nodes, notifier can resume message delivery from where it left off after it fails over to the new node.

How HAD Deletes Messages

The VCS engine, HAD, stores messages to be sent to notifier. These messages are deleted by HAD under the following conditions:

• The message has been in the queue for one hour and notifier is unable to deliver the message to the recipient. (This also means, that until notifier connects to HAD, messages are stored permanently in the queue until one of the following conditions are met.)

or

• The message queue is full and to make room for the latest message, the earliest message is deleted.

or

• VCS receives a message acknowledgement from notifier when notifier has delivered the message to at least one designated recipient. For example, if two SNMP consoles and two email recipients are designated, and notifier can send the message to only one email recipient because the other three were configured incorrectly, notifier sends an acknowledgement to VCS, regardless that the message reached only one of the four recipients. Error messages are also printed to the log files when delivery errors occur.